17/ -J I r/r— I J :3 ii- CORNELL UNIVERSITY LIBRARY BOUGHT WITH THE INCOME OF THE SAGE ENDOWMENT FUND GIVEN IN 1S9I BY HENRY WILLIAMS SAGE DAfE OUL fH^SEH^§^9 QM 451.T5''r" ""'"^^^'■•>' '-*^^0' ''°''nii(n"il„i!l',tlffi!)S, ..9.'„.t'!?„ central nervou 3 1924 024 791 216 Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924024791216 THE FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Copyright, 1920, By PAUL B. HOEBER All Rights Reserved Published, December, 1920 Printed in the United States of America THE FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM An Introduction to the Study of J\[ervous Diseases BY FREDERICK TILNEY, M.D. Ph.D. Professor of Neurology, Columbia University; Attending Neurologist, the Presbyterian Hospital, and the New York Neurological Institute, Consulting Neurologist, Roosevelt Hospital, New York AND HENRY ALSOP RILEY, A.M., M.D. Associate in Neurology, Columbia University, Associate Attending Neurologist, New York Neurological Institute; Attending Physician, Neurological Department, Vanderbilt-Clinic, New York FOREWORD BY GEORGE S. HUNTINGTON, Sc.D., M.D. Professor of Anatomy, Columbia University 591 FIGURES CONTAINING 763 ILLUSTRATIONS OF WHICH 56 ARE COLORED NEW YORK PAUL B. HOEBER 1921 DEDICATED TO Professor George S. Huntington In grateful recognition and affectionate appreciation of his teaching and friendship which have heen a constant guide and an unfailing inspiration for many years 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 Wnson 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 Com- ponent Theorj' of the Nervous Sj^stem. In this connection, we desire especially to mention Professors H. F. Osborn, C. F. W. McClure, O. 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 ad- vice in the photomicrography; to Miss Regina Unger for her unsur- passed technical skill in the preparation of histological sections of the brain and spinal cord; to I\Ir. R-an Summers for the original drawings; to Miss Alice Goldsmith for hei' painstaking work on the manuscript and index. It is difficult for us to express adequatelj^ our deep sense of appreciation for the courtesy, generosity and cooperation of our publisher, Mr. Paul B. Hoeber antl his editorial staff. F. T. October 6, lf)20 H. A. R. PREFACE FOE a number of years the authors have had the privilege of teaching neuro-anatomy to medical students in Columbia Univer- sity, 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 perti- nence 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 physio- logical 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 j^et 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 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 neurologj'. The interlocking facts of development, structure and function, and their interpretation under normal as well as pathological conditions, present an edu- cational 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 sj'stem fails to realize fully the difficulty of adequately presenting the enormouslj' 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 comV:>ine 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 illustratii-e material constitute for the neural morphologist the only a\-ailal)le authoritati^'e laboratory of experimental zoology in which morbid conditions, altering the normal physiological reactions, point to the morj^hological basis and afford the final and conclusive demonstrati(.)n of the functional significance underlying the details of organic structure. The medical curriculum, cliarged with many crimes of both omission and commission, is perliai)s nowhere blamed more justl}' than in its fatal heterochronic assignment of the correlated and mutually supplemental topics of morphological and clinical neu- rology to different parts, and mostly to different years, of the course, thus depri\'ing each of the iii(lis])cusal)le aid of the other which a synchronous consideration would afford. These considerations led a number of years ago at Columbia UniA-ersity to the uniting of tlie structural, functional and clinical FOREWORD A RECENT issue of "Science"^ records, under " University and Educational News," a significant change in medical edu- cational 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 teach- ing 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 re- action 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 medi- cine 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 primarilj- are concerned. I Vol. XII, No. 1343, Sept. 24, 1920. ix xu FOREWORD confident that they will likewise find their task made lighter, their vision cleared and their mental outlook widened by the broad con- ception and stimulating presentation which enlivens the pages of this volume. On behalf of my University I wish to express our grateful appre- ciation of this product of a ripe American scholarship and training. George S. Huxtixgton Depart-Mext of Anatomy Columbia University October 8, 1920 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 establish- ment of which American Science has contributed so largely, this book offers its consideration of the vertebrate central nervous organi- zation 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 sj^stem, 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 publi- cation 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 pro- ductive study in the morphological laboratorj^ of this institution which have gone into the creation of this volume. As I have con- stantly 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 XIV CONTENTS CHAPTER IV Pace THE UNIT OF STRUCTURE OF THE NERVOUS SYSTEM— The Nerve-Cell OR Neurone 50 Adaptation to the Purposes of Generating and Condueting Nerve Impulses — Structure of the Neurone — The Cell Membrane — The Cytoplasm — Intra- cytoplasmie Canals — Chromophilic Sulistances — 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 SYSTEAI— The Neurone Theory 71 The Manner in Which Nerve Cells Establish Intercommunications — Classifica- tion of Cells Encountered in the Nervous Sj'stem — Dynamic Polarization — The Neurone Theory — Contact Contmuitv — Synapsis — Interpretation of the Centrahzation of the Nervous System — The Essential Relation of the Re- ceptors to the Effectors — The Receptors — Exteroceptors — Contact Receptors — Distance Receptors — Proprioceptors — Interoceptors — The Effectors — Func- tional Significance of the Somatic Receptors — Simple Tactile Sensibility — Critical Tactile Sensibility — Pressure Sensibility of all Grades — Muscle- Joint Sense — Pain Sensibility — Temperature Sensibility — Equilibratory Sensi- bility — 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 /A' 67Tr . . 94 Significance of Spinal Relations — Incision Through the Skin and Subcutaneous Tissues — Depth of Incision m the Several Regions — Separation of Muscle Masses — iSIuscles and Fascia^ I^xposed — .\rteries Encountered in the Ex- posure — Periosteum and Bone Expo.sed — 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 Alater — The Subarachnoid Space and Spinal Fluid — Ligamentum Denticulatum — Examination of the Cord and the Emergent Roots — Remo\-al of the Cord. CHAPTER VII THE SPINAL CORD — Its General Ch.\r.u:ter and Anatomy . 105 Form of the Spinal Cord — Regional Differences m the Spinal Cord — Significance of the Several Regions of the Spinal Cord — Dinn'iisions and Weight — General Relations — Means of Fixation — .Surface i\larkings — The Se\'eral 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 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 U Principle of Development in the Mammalian Embr^'o — 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 — Comple- tion of the Roof-Plate — Histological Changes in the Lateral Walls — Forma- tion 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 Mj'elomeres — The Encephalomeres. CHAPTER III EMBRYOLOGICAL DEVELOPMENT OF THE CENTRAL NERVOUS SYSTEM (Continued) The Central Canal and Primarjr 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, Ac- cessorius and Hypoglossus Nerves — Ganglion of Froriep and Ganglion Acces- sorius — Segmentation of the Neural Crest — The Spinal Ganglia — Constituents of a Typical Spinal Segment — The Optic Stalk and End-Vesicle — The Tri- geminal and Acoustico-Facial Evaginations — The Infundibular Evagination — The Otocyst — Aula and Hemispheriam — 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 Meten- cephalon and Myelencephalon — Histogenesis of the Neural Tube. xiii 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 Hemiseotion of tlie Spinal Cord— Symlrome of Complete Section of the Spinal Cord. CHAPTER XIII REMOVAL OF THE BRAIN AXD INVESTIGATION OF THE BRAIN CASE 243 The Cephahc Division of the Central Nervous System— Preliminary Pro- cedure 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 Require- ments of Respiration — The Gills — Eneephalomeres and Myelomeres — Control of the Medulla Over Respiration, Cardiac Action and Gastro-lntestinal Activity — The Necessary Increase of Gray jNIatter in the Medulla — The Development of the Fourth Ventricle — The Development i^f the Gustatory Sense — The Devel- opment of the Equilibratory Mechanism — The Development of Special Organs of Offense — The Primitive Functions of the Medulla — Alodifications Due to the A.s.sumption 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 — Modiflcafiims of the Face — The Influence of Suprasegmental Structures. CHAPTER XV THE .MEDULLA OBLONGATA— Relations, Subp.ace AprEARANXE and Anat- omy OF THE Medulla 205 Situation, Boundaries and Relations — Dimensions and Coverings of the Medulla — Arteries of the IMedulla 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 Con- nected with the Medulla Oblongata — Tlie Dorsal Root Ganglia of the Cranial Nerves Connected with the Medulla Oblongata. CONTENTS XV CHAPTER VIII Page THE SPINAL CORD— Its Coverings AND Circulation 119 The Osseous Covering — Spinal Dura Mater — Ttie 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 — Circu- lation of the Spinal Cord — Lj'mphatics of the Spinal Cord — The Practical Significance of the Spinal Cord and its Coverings. CHAPTER IX THE SPINAL CORD— HisTOLOGr OF 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 op the Gr-ay 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 A.ssociative Control — Vestibulo-Equilibratorj- Con- trol — Synergic Control — Associative Automatic Control — Voluntary or Voli- tional 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 AIusclcs 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 Connec- tions Which They Establish — The Three White Columns of the Cord — Con- stituents of the Dorsal Wliite Column — Intersegmental Fibers in the Dorsal White Column — Summary of the Functions of the Dorsal \Vhite Column — Constituents of the Lateral White Column — Summary of the Functions of the Lateral White Column — Constituents of the Ventral White Column — Summarj' of the Functions of the Ventral White Column of the Cord. CHAPTER XII THE SPINiVL 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 Write Matter — Clinical Syndromes as a Means of Interpreting Spinal Cord Function — Syndrome of the Ventral Gray Matter — Syndrome of the Dorsal Gray Matter: Xviii CONTENTS Page Tegmentum— Features m the Embryol.)gical 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 Mark- ings and Surface Features of the Pons Varolii— The Floor of the Fourth Ventricle —Features in the Floor of the Fourth Ventricle. CHAPTEPv. XXI THE PONS VAROLII— Internal Structure AND Histology OF THE Pox.s. . . 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 JIatter at the Level of the Nucleus Masticatorius— Arrangement of the Gray and ^\ hite Matter at the Level of the Decussation of the Trochlear Nerve— Summary of the Relations of the Gray and 'Wliite Matter of the Pons Varolii. CHAPTER XXII THE PONS VAROLII — Functions ano Princifal Syndromes op the Pons . . .3S3 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 tlie Pon.s — Simple Reflexes Mediated Through the Pons — The Pons in its Relation to Special Functions — Its Rela- tion to Respiration — Its Relation to Plioiiation — Its Relation to Deglutition — Its Relation to Secretion — Its Relation to Eye Alovemcnts and Hearing — Functions of the "White Matter of tlie Pons — DesceiKHiig Tracts Traversing the Pons — Ascending Tracts Traversing the Pons — Decussations m the Pons — Principal Syndromes of the Pons Varolii — Syndrome of the Head and E3'e- 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 Abduccns Nerve — Syndrome of the Pyramid, Fillet, Inferior Cereliclhir Peduncle and Posterior Longitudinal Fasciculus. CHAPTER XXIII THE CEREBELLUJNI — A General View of Its Evolutional Significance . . -107 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 — Lhiiformity of the Internal Structure of the Cerebellum — Primitive Connections of the Cerebellum — The Connections of the Cerebellum in Mammals — The Evolutional Sig- nificance of the Cerebellum. CHAPTER XXIV THE CEREBELLUM — Relations, Surface Appearance and Anatojiy .... 427 General Relations and Boundaries — Surface Relations — Dimensions, Weight and Coverings— Arteries of the Cerebellum— Parts of the Cerebellum— Sur- face Appearance of the Cerebellum— Surfaces of the CerebeUum- Cerebellar Lobation in the Human Brain — Fissures and Lobes of the Superior Portion CONTENTS XVll CHAPTER XVI Page THE MEDULLA OBLONGATA — Internal Structure and Histology of the Medulla 281 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 Decussa- tion — Changes in the Gray and White Matter at the Caudal Limit of the Inferior Olive. CHAPTER XVII THE MEDULLA OBLONGATA — Internal Structure and Hlstoloqy of the Medulla (Continued) 305 Changes in the Gray and White Matter at the Level Through the Middle of the Inferior Ohve — 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 . 31G 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 Respira- tion — Its Relation to Phonation — Its Relation to Deglutition and Digestion — Its Relation to Cardiac Action — Its Relation to Metaboli.sm, 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 — Sj'ndrome of the Pyramid and the Hypoglossal Nerve — Syndrome of the Mesial Fillet, Pyramid and Hypoglossal Nerve — The Syndrome of the Nucleus Ambigiuis and Nucleus Accessorius — Syndrome of the Nucleus Ambiguus, Nucleas Accessorius and Nucleus Hypo- glossus — Syndrome of the Nucleus Ambiguus and Spmal 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 Ob- longata — Syndrome of Babinski-Nageotte — Syndrome of Cestan-Chenais. CHAPTER XX THE PONS VAROLII — Sionificancb, Anatomy and Embryology of the Pons 358 The Pons, a Structure of the Mammahan Brain — Significance of the Pons — The Pons an Index of Cortical Development— Significance of the Metencephalic XX CONTENTS CHAPTER XXX Page THE MIDBRAIN— The FuNCTiONs and Principal Syndromes of the Mesen- CEPHALON "^^'^ 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 tlie 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 IMatter — Syndrome of the Interpeduncular Space — Syndrome of the Cerebral Peduncle — Unilateral Tegmental Syndrome of the Midbrain. CHAPTER XXXI THE INTERBRAIN — The Genek.u, Skjnificance or 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 Intcrljram. CHAPTER XXXII THE INTERBRAIN — Anatomy and Embryology of the Diencephalon . . , 569 Situation, Boundaries and Relations of the Interbrain — Parts of the Inter- brain — The Hypothalamus — The Optic Chiasm — The Post-Chiasmatic Emi- nence — The Stalk of the Infundibulum and Infundibular Process — The Post- infundibular Eminence — Corpora Mammillaria — The E])ithalamus — The Tela Chorioidea Superior or Velum Interpositum — The Pineal Gland — Relations of the Pineal Gland — The Posterior Commissure — The Thalamus and Sub- thalamus — The INIetathalamus — The Third Ventricle — Embryology of the Diencephalon. CHAPTER XXXIII THE INTERBRAIN — Internal Structitre and Histology of the Dien- cephalon 539 Section at the Level of the Mammillary Bodies — Section at the Level of the Tuber Cinercuni — Section at the Level of the Optic Chiasm — Section at the Level of the Ansa Lenticularts — Section at the Level of the Anterior Com- missure — Principal Nuclei of the Diencephalon and Their Significance — Connections of the Diencephalon and Tlieir Significance — The Diencephalon as a Relay in the Somatic and Splanchnic Sensory Patln\-ays — Tlie Thalamo- Telencephahc Connection — Subthalamic Connections — Decussations in the Diencephalon — Commissures of the Dienceijhalon. CHAPTER X-XXIV THE INTERBRAIN — The Functions and Principal Syndromes of the Diencephalon qqq Functions of the Thalamus and Mctathalamus— Functions of the Subthalamus — Functions of the Epithalamus— Functions of the Hyixithalamus- Principal Syndromes of the Diencephalon — Syndrome of the Thahimus — The Syndrome of the Subthalamus— Syndrome of the Hypothalamus— Syndrome of the Epithalamus. 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 Vitas CerebeUi and the Medullary Nuclei of the Cerebellum. CHAPTER XXV THE CEREBELLUM — Internal Sthuctube, Histoloqy and Emeryologt . . 445 The Histology of the Gray Matter of the Cerebellar Cortex — The Molecular Layer — The Granular Layer — Summary of the Cellular Elements in the Cere- bellar 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 Varia- tions 47.5 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 of the Mesencephalon 4S.5 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 — Telencephahzation — The Significance of the Tegmentum and Basis Mesencephali — Embryology of the Mesencephalon — Differentiation of the Corpora Quadrigemina — Histogenesis of the Midbrain — Anatomy of the Alesencephalon. CHAPTER XXIX THE MIDBRAIN — Internal Structure and Histology of the Mesen- cephalon 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 Mesencephah — "iVhite Matter of the Basis Mesencephali. XXll CONTENTS CHAPTER XL Page THE ENDBRAIN~Thb Cranio-Cerebral Circulation 714 The Arterial Circulation of the Brain — General Arrangement of the Arterial Circulation — The Circle of Willis — The Tributaries of the Circle of Willis — The Arteries of the Convolutions — Tabulation of the Arterial Circulation for Each Area — The Venous Drainage of the Skull and Its Contents — General Divisions of the Venous Circulation — The Venous Pressure — The System of the Dural Sinuses — Communications between the Extra- and Intra-Cerebral Cir- culation — Practical Considerations in Regard to the Dural Sinuses — The Diploic System of Veins — The Venous System of the Cranial Integument — The Veins of the Cerebrum and Cerebellum. CHAPTER XLI THE ENDBRAIN — The Cortex of the Cerebral Hemispheres "43 Cortical Stratification — Strata of the Cerebral Cortex in Man — The Cellular Strata of the Cerebral Cortex — The Plexiform Layer — The Layer of Small Pyramidal Cells — The Layers of the Medium-Sized and Large External Pyra- midal Cells — Layer of Stellate or Granular Cells — The Layer of Large Internal Pyramidal Cells — Giant Cells — The Layer of Fusiform Cells — Tabulation of Cortical Cells and their Processes — Neuroglia of tire Cerebral Cortex — The "Wliite Matter of the Cerebral Cortex — Relations of the Cellular Strata to the Fiber Zones of the Cerebral Cortex. CHAPTER XLII THE ENDBRAIN — The IMedullaby Substance of the Cerebral Hemispheres 7.59 Distinctive Features of the Medullary Substance of the Endbrain — Fiber Constituents of the Medullary Substance — The Association Fibers of the Cerebral Cortex — Short Association Fibers — Long Association Fibers — The Commissural Fibers — The Corpus Callosum — Anterior and Hippocampal Com- missures — Projection Fibers of the Cerebral Cortex — Neopallial Projection System. CHAPTER XLIII THE ENDBRAIN — Functional Significance and Principal Syndromes of the Medullary Substance 779 Functional Significance of the Short Projection Fibers — The Thalamic Radia- tions — The Radiation of the Superior Colliculus of the Midbrain — Radiation of the Mesial Geniculate Body and Inferior Colliculus of the Midbrain — The Radiation of the Nucleus Ruber — The Functional Significance of the Long Projection Fibers — Summary of the Arrangement of the Projection Fibers in the Internal Capsule of Man — Syndromes Due to Lesions Involving the Internal Capsule — Syndrome Due to Unilateral Lesion of the Pyramidal Sj^stem in the Internal Capsule — Syndrome Due to Bilateral Lesion in the Cortico-Nuclear Contingent of the Pyramidal System — Syndrome of the Carrefour Sensitif of Charcot — Syndrome of the Thalamus and Internal Capsule — The Projection Systems of the Rhinencephalon — Functional Significance of the Projection Systems Entering into the Rhinencephalon. CHAPTER XLIV THE ENDBRAIN — The Internal Nuclei op the Cerebral Hemispheres . 798 The Internal Nuclei or the Basal Ganglia — The Corpus Striatum — The General Significance of the Corpus Striatum — Connections of the Corpus Striatum — CONTENTS XXI CHAPTER XXXV Page THE ENDBRAIN~Thb Cerebral Hemispheres 626 The Significance of the Endbrain — The Cerebral Hemispheres — The Endbrain in Relation to Animal Behavior — Individual and Generic Behavior — Mech- anism of the Endbrain in the Expansion of Experience — The Endbrain in the Several Classes of Vertebrates. CHAPTER XXXVI THE ENDBRAIN — Surface Anatomy of the Cerebral Hemispheres . . . 640 Surface Appearance of the Hemispheres — Cerebral Fissures — Interlobar Fissures of the Cerebral Hemispheres — Fissures of Sylvius and of Rolando, Parieto-Occipital, Collateral Calloso-Marginal and Calcarine Fissures, Limiting Sulcus of Reil — The Lobes of the Cerebral Hemispheres — Frontal Lobe — Par- ietal Lobe — Occipital Lobe — Temporal Lobe — Insula or Island of Reil — Limbic Lobe or Archipallial Rhinenccphalon — The Primordial Rhinencephalon — Summary of the Parts Entering into the Formation of the Rhinencephalon. CHAPTER XXXVII THE ENDBRAIN — Development and Comparative Morphology oe the Ci^re- BRAL Hemispheres , 6G3 The Two Principal Elements of the Prosencephalon — Differentiation of the Eotoptic Zone of Schulte — Development of the Lateral Telencephalic Evagina- tions, the Hemispheres — Development of the Corpus Striatum — Divisions of the Corpus Striatum — The Rhinencephalon — Archipallium — The Neopallium — The Sylvian Fossa — Histogenesis of the Walls of the Neopallium — The Myelo- genetie Fields of Flechsig. CHAPTER XXXVIII THE ENDBRAIN — Cerebr.al Me.\surements and Cranio-Cebebral Topog- raphy 6S1 Shape, Situation, Boundaries and Surfaces — Dimensions and Weight of the Cerebral Hemispheres — Comparative Measurement of the Extent of Surface of the Cerebral Convolutions — Thickness of Cortex — Brain Weight — The Relative Weight of the Brain to the Body — Relation of Stature of the Body to the Brain Weight — -Brain Weight in Different Races — Weight of the Brain Cells — Cranio-Cerebral Topography — The Relations of the Convolutions to the Skull — The Projection of the Lateral Ventricle on the Surface of the Skull — Cranial Points — Cranial Indices. CHAPTER XXXIX THE ENDBRAIN— The Coverings OF THE Br.un 69.3 The Significance of the Coverings of tlie Brain — The Embryological Develop- ment of the Coverings — Location of the Coverings — The Osseous Covering — The Cranial Dura Mater — The Dural Reduplications — The Minute Structure of the Dura Mater — The Arachnoid — The System of the Arachnoidal Cisterns — The Pacchionian Granulations — The Minute Structure of the Arachnoid — The Cerebrospinal Fluid — The Pia Mater— The Cliorioidal Glands — Com- munications between the Ventricular Cavity and the Subarachnoid Space — Minute Structure of the Pia Mater — The Blood Vessels of the Cranial Meninges — The Vessels of the Pia Mater — The Arteries of the Dura Mater — The Veins of the Dura Mater — The Lymphatics of the Meninges — The Nerves of the Meninges. XXIV CONTENTS CHAPTER XL VIII I'age THE ENDBRAIN— The Limbic and Insular Areas 879 Constituents of the Limbic Area — Archipallial Rhinenoephalon — The Gyms Cinguli — The Gyrus Hippocampi — The Subiculum — The Comu Ammonis — The Gyrus Dentatus— The Gyrus Fasciolaris, Gyrvis Uncinatus and G>'ri AndreiB Retzii—The Primordial Rhincncephalon^The Insular Area— Func- tional Significance of the Insula. CHAPTER XLIX THE ENDBRAIN — The Parietal Frontal and Prepkontal Areas S9-4 The Parietal Area — Functional Significance of the Parietal Area — The Frontal Area — The Prefrontal Area — Functional Significance of the Frontal and Pre- frontal Areas — Syndromes of the Frontal and Prefrontal Areas. CHAPTER L THE ENDBRAIN — Tub Inter.n'al Structure of the Hemisphere and the Ventricular System 912 A Series of Sections made in the Horizontal Plane — Immediately Beneath the Vertex of the Hemisphere — Through the Dorsal Portion of the Centrum Ovale — Through the Level of the Corpus Callosum and the Body of the Lateral Ventricle — Through the Atrium and Frontal Cornu of the Lateral Ventricle — Through the Thalamic Portion of the Internal Capsule — Through the Subthalamic Portion of the Internal Capsule and Anterior Cominissuro — Through the Cerebral Peduncle — A Series of Sections made in the Coronal Plane— Tlie Frontal Pole of the Frontal Lobe— Through the Cephalic Extremity of the Corpus Callosum — Througli the Tiji of the Frontal Horn of the Lateral Ventricle — Tlirougli the Pole of the Temporal Lobe — Through the Head of the Caudate Nucleus — Through the Cephalic Extremity of the Internal Capsule — At the Point of Confluence of the iMedullary Substance of the Temporal and Frontal Lolies — Through the Anterior Commissure — Through the Genu of the Internal Capsule — Through the Cephalic Extremity of the Cerebral Peduncle— Through the Cephalic Extremity of the Cornu Ammonis — Througli the Rctrolenticular Portion of the Internal Capsule — Through the Atrium ^'eiitriculi— Tlirough the Occipital Horn of the Lateral Ventricle— Through the Occipital Pole of the Hemisphere— The Lateral Ventricles— The Frontal Horn— The Pars Centralis— The Occipital Horn— The Temporal Horn— The Embryological and Developmental Significance of the Ventricular System. GLOSSARY 945 REFERENCi;S FtJR SUPPLEMENTARY READING 963 INDEX 977 CONTENTS XXm Pack The Projection Fibers — Radiations of the Corpus Striatum — Internuclear Fibers of the Corpus Striatum — The Lamino) Medullares — Penetrating Fibers and Possible Connections of the Corpus Striatum with the Cerebral Cortex — The Claustrum — The Amygdaloid Nucleus. CHAPTER XLV THE ENDBRAIN — Functional Significance and Principal Syndromes of THE Corpus Striatum SIO Experimental Investigation — Phjdetic Significance of the Corpus Striatum — Automatic Associated Acts in Man — Axio-Appendicular Automatic Associated Movements — Axial Automatic Associated Movements — Appendicular Auto- matic Associated Movements — Relation of the Motor Cortex to the Corpus Striatum — Abnormal Associated Movements of Clinical Import-ance — The Principal Syndromes of the Corpus Striatum — The Syndrome of the Globus Pallidus — The Syndrome of the Lenticular Nucleus (Putamen) — Syndrome of the Corpus Striatum (Particularly Affecting the Caudate Nucleus and Putamen) — Summary with Reference to the Function of the Corpus Striatum and Symptoms Due to Lesions in It. CHAPTER XLVI THE ENDBRAIN — Cerebral Localization — The Somatic Motor Area . . . 827 Methods by Which Cerebral Localization has been Established — The Method of Stilling — The Method of Gerlach — The Myelinogenetic Method of Flechsig — Method of Embiyological Arrest of Gudden — The Physiological Method — The Pathologico-Anatomical Method of Turck — The Clinico-Pathological Method — The Histological Method — Cortical Areas Distinguished by the Histological Method — Precentral or Motor Area — Functional Significance — Volitional Control — Inhibition — Stimulation of the Motor Cortex — Syndromes of the Motor Cortex — The Syndrome of Irritation — The Syndrome of Destruc- tion — The Intermediate Precentral or Psycho-Motor Area — Functional Sig- nificance — The Incentive Synthesis — The Motor Purpose — The Motor Con- cept — Syndromes of the Moto-Psychic Area — Special Forms of Motor Apraxia. CHAPTER XI.VH THE ENDBRAIN — Cerebral Localization — The Somestheto-Sensory, Visual and Auditory Areas 846 The Postcentral or Somestheto-Sensory Area (The Body-Feeling Sensory Area) — The Functional Significance of the Postcentral Area — Syndrome of the Postcentral Area — The Intermediate Postcentral Area (Somestheto-Psychic Area) — Functional Significance of the Intermediate Postcentral Area — Syn- dromes of the Intermediate Postcentral Area — The Caloarine or Visuo-Sensory Area — Functional Significance of the Visuo-Sensory Area — The Syndrome of the Visuo-Sensory Area — The Occipital or Visuo-Psj^chic Area — Functional Sig- nificance of the Visuo-Psychic Area — Syndromes of the Visuo-Psychic Area — The Transverse Temporal Gyri of Heschl or the Audito-Sensory Area — Functional Significance of the Audito-Sen.sory Area — Syndromes of the Audito-Sensory Area — The Intermediate Temporal or Audito-Psychic Area — Functional Sig- nificance of the Intermediate Temporal Area — Syndromes of the Intermediate Temporal Area. FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM ganic lesi(ni,s. Such, for example, are the cases of "shell-shock, ' ' in which a sud- denly developing paralysis may have all the appearances of a disease m the brain, in the spinal cord or in the peripheral nerves, and yet, when tested by anatomical rules, will prove themselves to be of another category altogether. Without knowledge of anatomy and physiology, it would be impossible to locate the position of iuan>' lesions which might be accessible to surgical interference. The signs whicli point to the anatomical level of injuries of the spinal cord, to involvement of the cerebellum, to affection of the occipi- tal, parietal, temporal, frontal and prefrontal areas of the brain, serve as guides to localization witliin the nervous system. How in- valuable, for instance, is the information that a patient is suffering from a bitemporal hemianopsia, a sign which almost invarial dy indicates the position of a lesion press- ing upon the ojjtic chiasm and in all prolialiility having its origin in the pituitary l)ody. The clinical value of such signs as aphasia, mind- deafness, mind-ljlindness, and the lack of the proper aljility to recognize oljjects by pal- pation, empliasizes the neces- sity of a clear understanding of the anatomy of the brain. Equipped with such knuw- ledge, the surgeon maA- with accuracy approach the seat of the trou))le producing the disturbance in the patii'nt. Neurology and the Prac- tice of Medicine. It is a general belief that the prac- ticing physician need know liut little of the nervcxis s^'stem. On the other hand, it has been estimated that from fifty to seventy per cent of the physi- cian's work is concerned with diseases of the nervous system. This statement does not seem an exaggeration when one considers the large nunil)er of cases coming into the clinical experience of every practitioner which represent that extensive group of disorders classed as tlie Neuroses. Here arc found many varieties of disturbances based upon no organic change, but which to each patient are real and often dominant factors in his life. Every organ and sys- tem in tlie l)ody has its well-recognized series of functional ner^'ous diseases, the treatment of which reciuires skill and judgment. But Ijeforo treatment Frc. 1. — .V cnsc diagnosed as :i spinal cord lesion, which proved to be hysteria and was eorn- )dcteh' cured Ijy psycliothera])\'. THE FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM AN INTRODUCTION TO THE STUDY OF NERVOUS DISEASES CHAPTER I THE CENTRAL NERVOUS SYSTEM ITS IMPORTANCE AND SIGNIFICANCE The Value of the Anatomy of the Nervous System in the Practice of Medicine. The anatomy of the nervous system to many physicians and medical students is reminiscent of struggles with complicated parts of the body which seem to have little practical value. It has an established repu- tation based upon its difficulties rather than upon the advantages of under- standing it. In large measure, this point of view may be ascribed to methods of approach which usually fail to make clear the pertinence of such knowl- edge. The study of the nervous organs is too often limited to the conditions of rigor mortis. It has come to be a citation of many labelled parts without re- gard to their dynamic significance, an exercise in pure morphology without the accompanying reasons for its importance and application to practice. Yet every phenomenon of human life is to some degree regulated by the nervous system, and there are few diseases which do not manifest defects in its controlling influences. This work is designed to fill the gap between morphology and the practical requirements of clinical medicine. It aims to visualize the living nervous S3^stem, to make accessible an appreciation of its vital relations to the func- tions which go to make up life, as well as the defects in these relations which result in disease. The diagnosis of nervous conditions, while in the main of interest to those particularly devoted to the studj' of neurology, has no little import- tance to all physicians. It is becoming more generally understood that neu- rological diagnosis depends primarily upon accurate anatomical knowledge and that without such knowledge many embarrassments may arise. There are no better illustrations of this fact than the common errors made in dis- tinguishing between the functional and organic diseases of the nervous system. The Great War has shown that there is a large number of disorders affecting the organism which may simulate disturbances due to actual or- 1 4 FOKiM .VXD FUNCTIOXS OF THE CENTRAL NEF.VOUS SYSTEM Ik.I.Is Ihc ciiliir tiaiiscnpl 1(111 of Die .■li:uij;v.s whkh have occuircd during the ovolutidiial period. 11 is iio.s.siWo to find evidence for iiiurli of tliis at present, and iinicli ivniams 1o l,e revcalcil. Not a.loiK' in Ihe liuinan body is tins evi- dence to lie sought ; a vast ariioiint. of it will he found in the lower forms of ajiiinal life a,iid in tlie einl.ryological develoi)iiieiit of the species. Such evi- dence cannot fail to make more clear our in.sight into the relations of the nervous system to the body as a whole. Comparati\-e ana- lomj' and embryology will be, in this sense, valualjli.' a.ids to our inter] iretation, and will furnisli numerous clews to the meaning of parts which otherwise could be scarcely moi-(^ than struc- tures recjuiring identification. The Centralization of the Nervous System. Con- cerning the iier\'ous system, it may properly f)e asked. What are its functions, and how does it serve the living animal? In stating lliis question, we should bear in mind that our inquiry deals with the generalized plan according to which any \ertel)rate animal is enabled to carry on the process of sustaining life. One striking leature about this process of living is that it results from a cooperation of many dilTer- I'lit structures; in fact, all |)arts of the body must act harmoniously if health and life are to he: preserved. It is often the case tliat organs wliich ]wrticipate in tiiis action are situ- ated at relatively great distances from each other, yet their activity must 1)0 synchronized in the rate and rhythm of their operation as well as in the (luantity and degri'e ol' their action. Such cooperation as this could not be left to chanei'; and so it has come about that its regula- tion lias been centralized in a set of organs known as the nervous system. 1. '/i.--.V c;LSe ill:i!.;llesrit ;i,^ I iv.stcri:!., wlui.'ll IIJK.)J1 Hulopsy |iiii\-cil to lie n c.-ise of \\ ilsim's dis- cuse, priigrr.ssivc li'iitiriil.-ir ilegonci';ition. THE CENTRAL NERVOUS SYSTEM may be applied to such disorders, it must be determined tliat they are in fact functional diseases. To make this decision requires the al.)ility to dis- tinguish between affections having no organic basis and those due to some actual tissue change. The frequency with which this differentiation fails to be made is well recognized. It is not an uncommon experience to find a case with some grave organic change receiving treatment under the diagnosis of neurasthenia, hysteria or a neurosis. There is a broader view, however, in the light of which ;lie phj'sician should be versed in the anatomy' of the human body. Since disease may be regarded as a deviation from the normal processes of life, a clear conception of these pro- cesses becomes fundamental. This presumes a knowledge of all the organs, of their indivi- dual as well as their integrative significance, and of the means by which they are brought inio and maintained in cooperation. It is not difficult to appre- ciate the necessity of luider- standing the normal workings of a mechanical device lieforc we undertake its r(>pair; yet it cannot be said that W(> have provided ourselves with such a full understanding of the human mechanism befoi-e we attempt the treatment of its disorders. In the main, we have made disease our chief interest. As a matter of fact, life is the principal theme, to which dis- ease is but a coroUarj'. The purel}' pragmatic attitude to- ward medicine is not without its defects. It fails to encourage an approach to the salient problems concerning the significance of life; it omits, as theoretical, the considerations of development and adajjtation. Although it lends facility to professional administration, it doc^s not estab- lish the philosophical attitude upon whicli the advance as well as tlie jirac- tice of medicine ultimately depend. The Evolutional Significance of the Central Nervous System. The human body is the consununation of a record made tlurnigh inestimable periods of time by adaptive modifications in the organic materials constituting life. The nervous system is rich in the record of these modifications; it probably Fig. 2. — A case dianuoseil is li\ -.ti ria, which upon further exaininatioii pi(j\fcl tu be a case of epidemic eneephahtis. 6 FORM AND FrXCTlONS OF THI^ CENTRAL NERVOfS SYSTEM Components of the Nervous System Controlling the Two Major Mechanisms. I<]ach of these niechaiusms comes umler the control of two principal divisions or components in tiie nervous system. One of these is represented by an extensive series of hiKhl}- sensitize(l organs calleil receptors, which are capable not only of detecting changes in or about the body but also of rapidly transmitting the impression of these changes todefimte stations whei'e the>- ma>' be registered and pioperly utilized. Tliis part is known as the affereiii or xenmnj component. Vejct&' DorscI VcvSO-dilator fiber Vcso-constrictor fiber 6ptcnchnic musculature fiber Gtanduiar effectorf iber — Pilomotor fiber ^Dopio-mc^icl cell column ^DorjO'lcitcrDl cell column Ventro-me3ial cell column Ventro.lc.terol cell column c^ondlion loture fibe ■ctor fiber fiber P'k;. 4. — Till' siimutir Hiiil spt'Liirhnic riiiapiiin-iit.s nf the nervous system. The second principal tlivision controlling each mechanism is I'eprcsented by an e(iually extensive series of organs called effectors, which are capable of activating some response, such as muscular contraction or the secretion of a fluid. This is known as the efferent or niotor component. It will lie seen that, taken together, tiiere are four components in the somatic and splanchnic mechanisms; these are: 1. The Somatic Sensory or Afferent Compontait. 2. The Somatic Motor or Efferent Component. .3. The Splanchnic Sensory or Afferent Component. 4. The Splanchnic Motor ov Efferent Component. Elach of these components occupies a definite territory in the spinal cord THE CENTRAL NERVOUS SYSTEM 5 In general, the animal lives through the operation of two major mechan- isms, one of which keeps it in contact with its environment, while the other controls its vital processes. THE TWO MAJOR MECHANISMS CONTROLLED BY THE NERVOUS SYSTEM Somatic Mechanism. The first of these two mechanisms, that which keeps the animal in contact with its environment, concerns itself in the strict sense wdth the management of the body. It is, so to speak, an externalizing mechanism. All of the movements of the limbs, the trunk and the head, which may be employed consciously or non-consciously for the purposes of the animal's welfare, are produced and regulated by this mechanism. It serves the requirements of obtaining food, of regulating that behavior with- out which starvation would ensue; it controls those reactions by means of which protection against inimical factors is provided, either through defensive or offensive acts; it furnishes all the complicated performances by which the animal is able to hold its allotted position as an individual and, in perpetuity, as a species. It is unquestionablj'' true that this me- chanism has afforded one of the chief means by which adaptation has been made to new envu-onment, and has thus laid the foundations for progression in the process of evolution. Because of its participation in these bodily activities, it is known as the somatic mechanisin. Splanchnic Mechanism. The second of the essential mechanisms has to do with the more intimate and vital activities of living, such, for ex- ample, as the circulation and respiration, digestion and elimination. Through its operation are administered the processes of absorption of essential nutritive material, of the chemical and physical treatment of such substances, of their proper assimilation and their distribution to the destinations in the bodj^ where they are emploj-ed as sustenance of life or transformed into vital energy. In this categorj'- also belong those func- tions whose main office it is to eliminate unnecessary substances which accumulate in the bod}^ as a result of the many chemical changes con- stantly going on. Because this has to do with the visceral functions, it is known as the visceral or splanchnic mechanism. The harmonious interaction of these two mechanisms is essential; should it fail, it is not difficult to conceive what disturbances might ensue. If, for example, when the whole organism is in need of nutrition, the somatic mechanism ceased to operate and the animal did not perform those acts necessarjr for obtaining food, it is easy to foresee what disaster would over- take the vital processes. Such examples may be multiplied indefinitely; but they all go to show the necessity of synchronism between the parts which have to do with somatic activities and those which regulate splanchnic func- tions. Their intimate interrelation is graphically illustrated in the conception that the somatic mechanism regulates the efforts of life, while the splanchnic mechanism controls the essence of life. 8 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM and its appendages. The purpose of these stiinuh is to create touch or tactile impressions which give rise to a type of sensation known as tactile sensibility {thigmesthesia[thigma, touch; esthesia, feehng]). The importance of such sensi- biUty is apparent. It is only necessary to observe the actions of a patient who has lost tactile sense m the hands to appreciate the serious hmitations in activity which this loss imposes. In addition to the epidermal surface of the skin, certain appendages, particularly the hairs, are important accessories for receiving surface stimuli. Another set of organs is especially designed to convey information con- cerning the temperature of the environment, whether it be the temperature of the air which surrounds the body or the fluid medium in which the animal lives. The tissues are adapted to a certain limited range of temperature, extremes above or below which are deleterious. To avoid destruction from such temperatures, the body is provided with organs which detect thermic changes. In addition to this primitive function of thermal sensibility, the ability to distinguish between degrees of heat and cold has furnished a valu- able means of sensory differentiation. Temperature sense is known as thermal sensibility {thermesthesia). It is not alone from the surfaces of the body that stimuli reach the nerv- ous system. In order that muscles may be equipped in such a waj' as to convey sensory impressions concerning their contractile status, their state of relaxation or tension, definite sensory organs are found among the muscle bundles. These are connected with nerve fibers and thus with the spinal cord and brain-stem. The significance of such a pathway from the muscles is apparent, since by this means the individual accjuires muscular awareness. If the avenues of this deep sensibility are interrupted, muscle sense is lost and it is no longer possible to direct corrective impulses in the adjustment of muscular acts. The results of such a disturbance are frequently seen in loco- motor ataxia, a common nervous disease in which the patient is no longer able to evaluate the character of his muscular movements and manifests in them an inaccuracy described as ataxia. The bones, the joints and the fascia? also have sensory organs which con- vey to the central nervous S3'stem impressions of much value in estimating the location and relations of the limbs and of the several parts of each limb, one to the other. Special sense organs located in the periosteum of the bones respond to stimuli giving information concerning the character of the surface upon which the individual happens to be standing or resting. Collectively, this is known as deep ■sensibility {bathesthesia). The special impressions coming from the muscles give rise to muscle sensibility (myesthesia) , those from the joints to joint sensibility (arthresthesia) . The bones, and the periosteum covering them, are provided with organs responsive to stimuli which deter- mine vibratory sensibility (paMesthesia.) . An important set of sensory organs giving information with reference to the spatial relations of the Ijody are tlie ■semicircular canals. These are minute, tubular structures in connection with the ear, so placed as to corre- spond to the three planes of space. They are filled with a fluid, changes in THE CENTRAL NERVOI'S SYSTEM I and brain, which constitutes its central portion. By means of afferent ami efferent nerve fibers, which form its periphei'al portion, it receives im- pressions from and despatches impulses to the structures undei' its control. In this light, the nervous system may be regarded as a structure performing its functions through the cooperation of four coordinate departments. It is not difficult to realize the manner in which such departmental organization contributes to the operating advantage of the entire organism. This concep- tion is known as the component theory of the nervous system. Cutaneous Sensihilily Ppriostpal SensihiUly 1. The Somatic Sensory or Afferent Component. This component fur- nishes the means of sensory intake from the entire surface of the body as well as from all of the skeletal structures. It is the great avenue bj' which all information from the outside world is received. Such information comes primarily to the somatic sensory receptors in the form of various stimuli. These stimuli may be received from the surface of the body bj^ contact through specialized end-organs. Organs of this kind are found in the skin 10 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM apparatus receiving stimuli from a drstance is the auditory mechanism, through the agency of which is produced acoustic sensibiltty (ncuesthesia). The specialized types of apparatus designed to receive stimuli from a distance are usually referred to as the organs of special sense. In a general way, this is a useful distinction; but on the other hand, each quality of sensi- bility is represented by a special sense of its own. The specialty of smell, hearing ami vision depends not upon a difference in kind but rather upon a dif- ference in the degree of specialization in the end-organs of these senses. As will be seen later, the organ for the recejjtion of tactile stimuli is highly specialized, although it does not approach the extreme morphological differentiation ex- hibited by the eye. All the structures designed to receive and transmit sensory stimuli from the surface and skeletal parts of the body constitute the somatic afferent ejr sen- sory component. One special feature concerning this component is variously interpreted by dift'erent authorities. Each of the several sense-quahties, in- cluding touch sense, temperature sen.se, deep sense and the distance senses, is capable under certain circumstances of giving rise to sensations quite at variance with that for which it usually .serves. Thus, tactile .stimuli may, under certain conditions, convey impressions to the brain which, in addition to the fundamental touch perception, provoke a sensation of discomfort, dis- tress or pain. It would seem that when the stimulus transcends the threshold of mere touch feeling, it tends to reach a level at which it causes actual pain. The significance of this becomes clear when we consider that such stim- uli are usually harmful to the tissues. In this manner tactile sense is equipped with an unusual pathwa}' by which impressions unusual in their severity may communicate the nature of their stimulation to the central nervous sys- tem which, in turn, responds by an adequate defense reaction. This same accessory protective apparatus is found running parallel with the course of every quality of sensibility. The usual and projier stimuli in each sense- quality pass by means of a customary pathway; but when these impressions become excessive and pain results, be it in the sphere of any type of sensa- tion, touch, temperature or muscle sense, then some part of the body is threatened by unfavorable circumstances, and the excessive stimuli follow a special pathwa}- to communicate this information to the central nervous system. This sensory element, forming the basis of a general protective mechanism, is known as pam sensihilitij (algesihesia). 2. The Somatic Motor or Efferent Component. It would be to little purpcse if all the vast amount of information collected by the human liody were not in some way utilized. This information has its real value because of the reactions which it determines and guides. In response to sensory impressions, the body carries out all its innumerable efforts at adjustment. There is no movement, no act, no course of Ixdiavior which is not initiated, executed or directed by the influence of body sensibility, so that these sen- sory influences are actually turned to definite account and made manifest as motion. For the most part, this type of motion is developed by the skeletal or striped muscles. These muscles are peculiar in that the>- are subject to the THE CENTRAL NERVOUS SYSTEM 9 which produce stimuli that are transmitted to the central nervous system and utilized in readjustments necessarj^ in maintaining the balance of the body. This is known as balance sensibility. In addition to the stimuli which gain access to the body through contact with its surface or originate in its skeletal structures, there are others which arise at a distance and are conveyed through the intervention of some me- dium, either air or water. The chief purpose of these stimuh is to direct the Muscle Sensibility (Myesthesia) Joint Sensibility (Arthresthesia) somatic actions with reference to objects outside of the body which the ani- mal purposes to approach or avoid. The most primitive of these distance stimuli are those affecting the sense of smell, for which a special apparatus has come into existence. The impression arising from this type of sensory stimuli constitutes olfactory sensibility {osmesihesia) . No less important are the dis- tance stimuli which reach the central nervous system by means of the visual apparatus, giving rise to visual sensibility (optesthesia) . A thud somatic sensory 12 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM by means of the sensory components are neither transitory nor evanescent, for each impulse leaves a lasting imprint on the nervous system. From the collected mass of these impressions grow the complex processes of sensory association which give rise to memory and at length develop the psychic combinations of individual experience. The apparently intrinsic, psychical operations of the brain may appear to beindependent of the four components, Spina! cord Afferent Efferent Fig. 8. — The splanchnic components. Afferent. — Thi.s innervation provides the means by which the sensory stimuli reach the central nervous system. Efferent. — This innervation provides the means by which the motor impulses are distrib- uted to the involuntary musculature regulating the vital processes. yet none of these higher syntheses would be possible without the funda- mental activities of the components themselves. In this light, the psychic life reveals itself as an elaboration of the synthetic interreaction of the components controlling the somatic and splanchnic mechanisms. Divisions of the Nervous System. For purposes of study, certain divisions of the nervous system mav with advantage be made; THE CENTRAL NERVOUS SYSTEM 11 will, and also in that the greater part of their activity is employed in the accomplishment of definite purposes. They are further peculiar because they may be subject to relatively long periods of inactivity during which no actual motofacient contraction occurs. All of the muscles operating in this way constitute the somatic muscles, and the portion of the nervous system allotted to their regulation is known as the somatic motor or efferent com'ponent. 3. The Splanchnic Sensory or Afferent Component. This component of the nervous system has to do with the receipt and transmission of sensory impulses arising in the viscera. Although these impressions do not always enter vividly into conscious- ness, they are none the less im- portant in initiating the glandular activities and smooth muscle con- tractions whose operations are necessary to the vegetative life. While for the most part the impres- sions received from the splanchnic sensory areas remain non-consciou.s, it is nevertheless apparent that there does exist an actual pathway from these areas into our conscious fields. This is illustrated in the sense of relief experienced upon the evacua- tion of the bladder or rectum. On the other hand, there may be a line of conduction, like the pathway for excessive somatic sensory impres- sions, less commonly traversed than that followed by the great majority of stimuli travelling in- ward, when the splanchnic sensory impulses transcend their usual, non-conscious level and become disagreeable or painful. This latter is an eciuipment making provision for a defense mechanism under circumstances which threaten or actually injure the tissues of the viscera. 4. The Splanchnic Motor or Efferent Component. The fourth component in the nervous sy.stem is that which directly controls the glands and the smooth muscles of the body. These, as has already been shown, perform their reactions in response to afferent impulses received through the splanch- nic sensory component. The Cooperation of the Four Components of the Nervous System. Through the four components of the nervous system already described, the activities of life are regulated and controlled. Impressions received FiCi. 7.— So- matic ef- f e r e n t component. This innervation provides the means by which m 1 o r impulses from the central nervous system reach the appen- dicular and axial musculature and thus control motor activities. CHAPTER 11 THE EMBRYOLOGICAL DEVELOPMENT OF THE CENTRAL NERVOUS SYSTEM Principle of Development in the Mammalian Embryo. The divisions of tlie nervous system are most easily understood in the light of their embry- ology. The description given here follows the general lines of development without giving reference to the finer details which will subsequently be dis- cussed in considering each division of the neuraxis. In order to obtam material which would show the series of steps from the beginning of this developmental process, it was necessary to select some form other than tlie human embryo, since satisfactory specimens, especially in the early stages, are difficult to obtain. In conscciuence a mammalian emliryo, fclis donicstica, which may be easih' procured, was chosen for this study. The principle of development in vertebrates depends upon the e^'olution of two long tubes lying in the longitudinal axis of tlie Ijody. One of these tubes occupies a dorsal position and becomes the ucura.vis or ccrchro.\jri)uiI si/stem. The second tube is A-entral in its position and gives rise to the ' period a third ele- ment grows between them, from which the supporting and motor strtictures of the t.iod)' develop. This is the mcsodcnn . It is to the more dorsal of the two tulies tliat we must direct attention, since from it the brain and spmal cord take origin. This tulje is deri^-ed from tlie outermost layer of the embryo, tire ectoderm. In the early cleavage stages, when the cells which form the ectoderm ari" first arranging themselves upon the outer surface of the splierical Ijod}' cif the lilastoderm, there are no signs of differentiation which indicate a tenilenc}- toward the formation of organs. All of the ectodermal cells appear to h-AVv the same gc^neral character and arrangement. Presently, however, there api")ears a faint streak on the outer stu'face of the spherical vesicle, wliich marks the general position and direc- tion of the longitudinal axis of the embryo. THE FORM.iTION OF THE XEUR-iL PLATE AXD GROOVE Almost immediately after the appearance of the priirriiivc streak, the cells of the ectoderm about it take on new activity anrl marked local changes be- come apparent. The ectodermal cells on either side of the long axis of the embryo begin to prohferate rapidly, until they form a relatively thick longi- tudinal plate which extends outward for a short distance u]ion either side of 14 THE CENTRAL NERVOUS SYSTEM 13 First, the cerebrospmal axis or neuraxis, which consists of the spinal cord and the brain. This portion of the nervous system is centrally placed in the body, the spinal cord occupying the vertebral canal and having its cephalic limit at the margin of the foramen magnum., while the brain comprises the portion of the central nervous system within the skull. Second, the 'peripheral nervous system, which consists of the cranial and spinal nerves, b}'' means of which impulses are transmitted from the surface of the body to the central nervous system and distributed from these organs to the muscles and the glands. Third, the vegetative or sympathetic nervous system which forms the connecting link be- tween the viscera and the cen- tral nervous S3''stem. It will be seen later that these major divisions are sus- ceptible of subdivision into parts which will require separate de- scription. In order that this study may be comprehensive and practical, each part will be discussed under the following headings: 1. General evolutional sig- nifiance. 2. Anatomy, embryology and histology. 3. Physiological significance. 4. Principal syndromes illus- trative of anatomical local- ization and functional signifi- cance. Peripheral Nerves Fig. 9. — Divisions of the nervous system in- cluding the cerebrospinal axis, the peri- pheral nerves and sympathetic system. IG FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM l:iecause it tlulimits the ectodermal cells destined to form the outer covering of the body from those giving rise to the cerebrospinal axis. Appearance of the Optic, Trigeminal and Acoustico-Facial Grooves. In the stage of two somites, the embryo shows two faiidy well-marked grooves running obliquely from within outward and backward near the cephalic ex- ti-emity of either neural fold. These obhcjue grooves are symmetrical in their position, in their form and in the depth to which they indent the neural folds. They mai'k the beginning of two evaginations which subsequently- protrude upon the lateral aspect of each fold near its cephalic extremity. Somewhat further caudally, along the crest of either neural fold, a second pair of grooves makes its appearance These grooves also extend obliquely from within out- ward, and although they are not as conspicuous as the first set, the}' are promi- FiG. 11. — Sr-ctions of embryos before and after segmentation. (Schnlle ami Tilney.) A. Tranaverse section of an embryo prior to tlie appearance of intersomitic clefts. 5. .Medullary plate. 7. Somatic ectoderm. 28. Region of transition. 29. Mesoderm. 30. Entoderm. B. Transverse section of an embryo ot one somite. 5. Medullary plate. 7. Somatic ectoderm. 28. Region of transition. 29. Mesoderm. 'SO. Entoderm. nent features at this stage of development. A third pair of grooves develops upon the summit of the neural fold at a considerable distance caudal to the second set. These three sets of grooves should be identified for further reference. The first set forms the optic grooves; the second, the trigeminal grooves; and the third, the acoustico-facial grooves. THE STAGE OF FOUR SOMITES Elevation of the Neural Folds. The embryo of four somites shows a pronounced atlvance in neural development. The neural fokls extend the entire length of the embryo from the cephahc to the caudal extremity. They are not, however, of the same height in all places. In their cephalic portion they have reached their greatest elevation and are approximately perpen- EMBRYOLOGICAL DEVELOPMENT OF THE NERVOUS SYSTEM 15 the long axis of the em- brj'O. At its lateral boundaries, the cells of the ectoderm still mani- fest their primitive a r r a n {j e m e n t . This central thickened area is the neural plate. A faint lonRitiidinal furrow appears near its center at an early stage. This is the neural groove. The concentration of cells occupying a central posi- tion in the embryo is thus divided mto two symmetrically bilateral halves, one of which lies on either side of the neural groove. THE STAGE OF T\\-0 SOMITES OR THE STAGE OF THE NEURAL PLATE This stage is observed in the embryo when tlie first two body segments have developed. The neural plate is somewhat heavier and more promi- nent at the cephalic ex- tremity, and the neural groove is correspond- ingly deeper here than toward the caudal end. The plate at the cephahc pole of the embryo has become elevated on either side of the groove to form the neural folds. At the edges of the neural plate a faint elevation marks the neuro-sonuitic junction, which is significant Xeura] i'latc Fig. 10. — Reconstruction of the stage of two somites in the development of the neuraxis; showing the forma- tion of the neural plate. (Schulte and Tilney.)' IS FORM AND FUNCTIONS OF THE r'ENTlJAL NER^^'OrS SYSTE^r ilicular in position. Tliis condition ohtains tlirougliout tin: coplialir, onc-thinl of the folds, l;>ut thereafter toward the tail, there is a gradual decrease in their height, while the walls formed by them are less perpendicular. In the extreme caudal areas the folds show liftle elevation ami llie neui-al groo\-e expands to form a semicircular depression. This pronounced change is the result of a gradual rising in each fold until what was previously its dorsal surface now faces inward toward the corresponding surface of the opposite side. As the cephalic borders of the two folds arc not yet in contact, there is a cleft between them. The process which results in this elevation of the neu- ral folds ultimately brings the two halves of the ni'ural plate uito more inti- mate relation witli each otlier. A connection Ijetween the two lateral walls already exists and forms tlu' Jloor-plate. The walls of the neural folds have ':'2fK • -■-•f.:lli*. ■*"*«*»,l; '>«.l i'-ft.lfll«f*^t»i.'..l.» 29 't^^Jt Fig. 14. — Sectioi A, Transverse section < ; of I if Iwn aiid tlirce somites. (SchiiUe and Tilneij.) oE transition showing presen.eof ashallow turro;. 29. •Mesoden"';^^' Entlde?m"*" ''"''"'"■ "*■ ^^S'°" Re.L^5^^S»n^';^°'\;:!,Zr^°^t^Scr;i.^°"'*^^- '■ '"^^'"""^ '"="- ■■ ^°-=*- -*°derm. 2S. grown greatly in thickness. In the earlier stage, thr neural plate m its thick- est region was compiis.'d of fom- or fiy,. layers of cells. Now the neural folds particularly in the cephalic region, consist of ten to twelve layers of cell-' More caudally, however, the thickness of the walls varies fron". six to eight ceUs. The innermost layer bordering upon the neural groove is m a state of active proliferation. Numerous karyokmetic figures are observed and rapid cell division is m process. As the new cells form, thev move away from the cen- tral groove mto a more lateral position m the wall. The only elements enter- mg into the formation of the folds, however, are ectodermal cells the mass of whose deeply staining bodies constitutf.s the most conspicuous 'feature' in the cross section of the embryo at this stage. There is no evidence of blood vessels or vascular development at this time, so that the nutrition of the relatively dense mass of the neural folds must be provided ]>v special means EMBRYDLOGICAL DEVELOPMENT OF THE NEm'OUS SYSTEM 17 -Cf-phalic ExtrpriiitN tBrain End) , Optic Groove . Nuural Fold ■ Neural Groove , Tri^ijininal Groove _ Acriustico-facial Groove — Somatic Ectode Neural Ectoderm Fic.-it Step In the Furnia- tioii of the Brain (I'Jriccphalon) OptJe \'csir]e Neuropore iSoiiKitic Ectoderm Roof Plate of JNIidljrain TriiL^eiiiinal Crest Neural Hiatus Acoustico-facial Crest Neural Hiatu3 Spinal Cord (Myclon) I Central Canal ■ Neuro-somatic Junction -j Caudal Extrenilt;^' da! Extremity Fig. 12 — Kn nji-truction of the stage of four Fig. 13. — Reconstruction of the stage somites sho^ving the elevation of the neural of eight somites showing the folds and the development of the neural formation of the neural tube, groove. {Scliultc and Tilncij.) (SchuUr and Tilneij.) 20 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM for a considerable time, m open communication with the cavity of the amnion. In this manner the amniotic fluid comes into relation with the waUs forming the neural folds. Inasmuch as the dense mass of cells forming these folds are not provided with blood vessds or lymph channels, they must have other means of obtaining nutrition. It is not improbable that this means is furnished by communication with the amniotic cavity, and that the process of metabolism is mediated through the amniotic fluid. In this sense, the central nervous system is primitively ecjuipped with a system of irrigation entirely different from its ultimate condition. This system pro- vides a direct method to satisfy nutritional demands and probably has its prototype m certain lower forms of life. In some of the inverteljrates, the '^ J^^^^ Fig. 1G. — Traii.s\-cibe section ol' tlic embryo of four somites. (Schiilk and Tiliiey.) 3. Trigeminal sulcus. ~j. MrJullary fold. 7. Somatic er'torlerm. nervous system is devoid of Ijlood vessels and h'mph channels; it depentls for its nutrition upon a water-vascular system whicli furnishes a circulation for the central nervous organs. Water is received Ihiuugh the mouth and conductey the more cephahc protuberance of tlic eye. This caudal evagina- tion is indicated by a shallow groove on the inner wall of the neural fold. EMBRYOLOGICAL DEVELOPAIEXT OF THE NER^OI'S S"i STEM 1!) The Neural and Somatic Ectoderm. The relation of the somatic and neural ectoderm has assumed a new significance. The neuro-somatic junc- tion upon the left has been drawn into closer relation to the corresponding junction upon the right, in preparation for the final closure of the somatic ectoderm across the dorsal surface of the neuraxis. The junction itself is in- dicated at this period by a sharp angle along the line of transition between the neural and somatic ectoderm. This transition is marked b}- a pronounced change in cellular characters. The somatic ectoderm is composed of two or three layei-s of epithelial cells, while the neural ectoderm consists of ;i dense stratified mass constituting the neural fold. Changes in the Mesoderm. The cells of this intermediate layer between ectoderm and entoderm ha^-e proliferated rapidly and now form a mass of Fiu. 15. — Transverse ser-tion of the embryo of four somites. (Scliulte nud Tiltny.) 1. Optic sulcus. '-. Tubercle of the floor. .3, .\fedullar\' fold. 7. Somatic ectoderm. loose, spongy tissue bordering upon the ventral and lateral surfaces of the neural folds. This tis.sue, the mesenchijme, is assuming a po,sition favorable to the ultimate support and protection of the central nervous system. Along the outer edge of each neural fold, a few mesenchjane cells make their way inward by penetrating into the spaces between the larger ectodermal eli'- ments. This process marks the Ijegimiing of a mesench^-mal invasion whicli lays the foundations for the blood vessels in the brain and spinal cord. The notochord, which is situated ventral to the floor-plate throughout the greater part of its extent, fails to reach the cephalic extremity of the neural groove. This relation to the notochord determines the epichordal and prochordal portions of the neuraxis. Probable Significance of the Neural Groove. The references already made to the neural groove indicate that in its cephalic extremity it is a deep and narrow cleft between the two opposing neural walls. The groove becomes more shallow and finally disappears in the caudal semicircular depression. In all embryos having an amniotic cavity the neural groove is, oo FUUM ANU FUNCTIONS OF THE ('1':nti!AL NKiaors sistem _< >iitii: Vesicle '^' I Neural Hiatus _Tri{;eminaI Crest '* J __\rural Hiatus Xeural Crest Transition bctweuri Hrain and Spinal Cord iiral Hiatus C;raiH:ul of tlic fuKioii of the futeral walls across the luidliiie, the neural folds are still widely separated, and bound an opening which IS known as the neuropore. Caudal to the fusion forrains the roof-plate, the separation between the neural folds is known as the neural hiatus. The walls of the neural folds have at this stage shown no pronounced changes other than the thickening in the region of the head, and the greater elevation due to a massing of the cells as the cephalic extremity of the neuraxis f^egins to expand. Fusion of the Somatic Ectoderm. The neural and sumatic ectoderm present a further alteration m their relations. This is evident in the area where the neural folds have fused across the mid-doi'sal hue; to f(nm the roof- plate. At the point of this fusion the neural antl somatic ectodeiias are separated, and the somatic ectodermal layer, following the ex- ample of the neural cells, lias formed a fusion across tli(> mid-dorsal line. In this region there is a layer of somatic ectoderm stretched directly across the tlorsal aspect of the roof- plate. In the more cranial regions the somatic and neural divisions of the ectoderm still maintain their original relations to the neural folds. This IS also the case in the region im- mediately caudal to the roof-plate, in which position the neural folds are still separated from each other. This separation is more marked than in the region of the iK.'uropore, although it is imf dithcult to appreciate in anticipation (hr course of events consecjuent upon complete fusion of the neural folds which results in the ultimate formation of the neural tulie. Invasion of Mesenchymal Cells. Tli(> mesoderm surrounding the neural folds, has increased in the nuiiilier of its cells, and tlie evidence of the mesenchymal iiivasi{.in into the folds is more marked than in the earlier stages. In some |)laces (here ar(> clusters of stage of ten somites showing mesenchymal (;ells which participate m the formation of neuraxis. (Srhulte vascularization of the central nervous system. '""' Ti^"<'!J''i At this period th(^ evaginations upon either f Fig. 18. — Ilec.unstniction of the EMBRYOLOGICAL DEVELOPMENT OF THE NERVOUS SYSTEM 21 The chief difference between it and the optic evagination is that it does not contain an extension of the neural groove. The more caudal of the two sets of protuberances becomes the trigeminal crest from which the Gasserian ganglion develops. A third pair of protuberances upon the dorsal aspect of the neural fold correspond in general character to the trigeminal crests. These outgrowths have a slight groove which indicates their position on the inner surface of the neural fold, but they contain no actual extension of the neural groove. They constitute the acoustico-facial crests from which arise the dorsal root ganglia of the vestibular and cochlear divisions of the eighth nerve and the geniculate ganglion of the seventh nerve. Fig. 17. — Transverse section of the embryo of four somites. (Schulte and Tllney.) 4. Acoustico-facial sulcus. 5. Medullary fold. 7. Somatic ectoderm. THE STAGE OF EIGHT SOMITES In this stage, certain critical changes have occurred which mark the in- ception of the transformation of the neural groove into a neural canal and the neural folds into an actual neural tube. The folds have undergone still further elevation, particularly in the head region. In many places these folds are nearly in contact, although at their most cephalic extremity thej- are still separated bj' a considerable distance. Formation of the Roof-Plate and Neuropore. In one area, however, the folds have come into actual contact and a fusion across the middle line has been completed. The deep cleft between the neural walls of this region has in this manner acquired a roof. The fusion thus produced is limitetl in extent and involves but a small area in that part of the neuraxis which is to give rise to the brain. Caudal to this fusion the separation between the neural folds grows wider as the tail is approached. The region in which fusion has taken place presents three distinct topographical structures: 1. The two lateral masses or ivalls forming the lateral boundaries of the neural tube. 2. The floor-plate marking the original position of the neural groove. 3. The new element just formed by fusion at the summits of the lateral walls across the median line, the roof-plate. 24 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM side of the cophalic oxtreniily of the neural folds are the most conspicuous elements in the head region. These ajytic evagina- tions are not only the first to appear in the de- velopment of the tubes, but they are, in the early stages, the most conspicuous outgrowths from the brain. Both the trigemmal and (icoustico- fiicinl crests have increased in size. Differentiation of Spinal Cord and Brain. Immediately caudal to the acoust ico-facial crest, the neural folds become rerluced in all rliameters, and although it is impossiljle to detect a definite constriction, the transition from the brain to the spinal conl is now dLscernible. A differentia- tion has finally been estabhslied betwcjcn the purt of the neuraxis which will give rise to the lirain and the jxirtion from which tlie spinal cord takes origin. Optic \'esic]c Pro.soncepbalon Mryencx'plialoii 'rrifioniiiial (.'riv.t Hhiiinbenceplialon Ni'ura] Hiatu.^ Neural Crest Transition lietwt Brain and .^pii Cord THE STAGE OF TWELVE SOAIITES Neural Hiatus Completion of the Roof -Plate. In tliis stage, the neural fohls liave almost completed their fusion across the mid-dorsal line. In the region cranial to the original formation of the roof- i:)late, the dorsal extremities of the neural folds liave come into contact and fused, thus complct- ii,,oi Plate iiig the roof-plate over the entire cephalic ex- tremity of the lirain. Caudal to the pirimary fusion of the neural folds, the roof-plate is now completed with the exception of several areas in which small apertures still persist. Twv or three of these openings may lie fduiid immediately caudal U) the jiosition of the trigeminal crest. At (lie cauilal extremily of the neural folds, there is still a large oiicning, aKliough the folds themscl\-es are ra|jidly rising and api)roaching each (it her. With tile cxce|itiiiii of the several ,^ ^, ,,., ,, ^^ li/dtiis tdrcady mentioned and 1lie large unfused slnicliiiri r.f tlic '''^ion "' fl'c Caudal extremity, the neural grotive stage of tweh'c has Iieen coiiverlrd inio ,a canal li(iuiidc(l bj' two somites showins lateral walls, a il(i I s Til EMBHYCJLOGICAL DE\-KL()PMENT OF THE NERVOUW SYSTEM 23 ^--■•..flw-^ -• Fig. 19. — Transverse section passing through the optic vesicles of an embryo of eight somites. (Srhidtc mid Tiliivij.) 1. Optic sulcus- .">. ?\Iednllary plalo, 7. Somatic ectoderm. Fig. 20. — Transverse section pa,ssing through the anlage of the trigeminal ganglion of an embryo of eight somites, (lichulte layer. It is, in faet, due to inisnilioa of eells rrom llie duvsal i'e ectoderm. This is the cvlis /ilatc, which sul:)Se((uently participates in the formation of the derma- lomes or cutaneous segments of the botiy. The irregular ventro- lateral mass of cells is the ,1 — AntprloT TOot. B — Posterior root. C — Primitive neuroblast. . i ■ i iJ— Commissural neuroblast. B— .Motor rolls already supplied mijotonte irOlll "WhlCtl ailSe with dendrites. F — Motor neurone provided with its cone of , , , growth, a — Neuroblast supplied with an internal liraneh. i- — tllC S (> g 111 e 11 t a 1 lUUSCUlar t'omniissiiral cone ol' growth '/ — Sensor\' bipolar erll i -i ,i ■ i structures, wlule the mesial mass of the somite is the sclcfolo/nr from a |)ortion of which the bony structures surrounding (he neural tube take origin. Each pair of somites is separated from the next succeeding pair by an appreciable interval m which there is a rarefaction of tlit^ mesenchyme ce|ls. The somites are not in direct contact with the nein-al tube, being se|)aratetl finni it by a consideralil(> mass of interposed mesenchymal cells. These cells form a loose, sjjongy tissue. The line of contact between the mesencliymal cells and the neural tulie is characterized by a tlenser layer containing a rich capillary network of l.)lood vessels. This condensali(.)n of the mesenchyme, perineural in position and Fm. 24. — Corrl of an (.■iiiUiyo rliu-kuii at tin' '■: of incutiation. Golgi'.'; iiietliod. (Cojul.) EMBRYOLOGICAL DEVELOPMENT OF THE NERVOUS SYSTEM 25 dorsum of the neural tube. As a result of this process the somatic ectoderm has detached itself from the neural ectoderm, at the same time concealing the neural tube beneath the surface and constituting a complete outer covering for the body. Histological Changes in the Lateral Walls. Critical changes in the lateral waUs have resulted in the formation of several strata of cells. The innermost of these cellular layers stains darkly and consists of two or three rows of cells. This is the ependymal layer. Adjacent to it is a less compact stratum. This constitutes the mantle Za^/e/-, surrounding which is a thin, homo- geneous mass, somewhat reticular in structure, containing but few cells and made up for the most part of nerve fibers. This is the medullary layer. Many karyokinetic figures appear in the ependymal layer indicating rapid cell multiplication, for this structure is the germinal region from which the new elements of the nervous svstem take origin. The cells constituting the mass Fig. 23. — Transver.se section of an embryo of sixteen somites, showing the closure of the neural tube completed prior to the appearance of the ganglionic crest. {Schulte and Tihiey.) 5. Neural tube. 7 Somatic ectoderm. of the mantle laj'er consist of neuroblasts and sjjongioblasts. The spongioblasts become differentiated to form the nei«-ogZm or supporting tissue of the nervous system, while the neuroblasts give rise to the neurocytes or nerve cells, the active functional elements of the neuraxis. Formation of Blood Vessels. Vascularization of the neural tissue has been carried to the point where it is possible to recognize that the mesen- chymal invasion has given rise to many isolated blood vascular spaces which, bj' their confluence, have formed a rich intrameduUarj' plexus of capillary vessels. The Neural Crests. Along the dorsal aspect of the neural tulie, upon either side of the roof-plate, there appears a long ridge of cells produced by a protrusion from the lateral walls, the neural crests. These two crests are paral- lel with each other and extend along the neural tube as the direct caudal continuation of the trigeminal and acoustico-facial crests. Upon histological examination, the neural crests appear to lie made up 2S FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM dilatation of the neural tulie. In lliis manner the tlrrcc primitive resTcIcs of the brain are differentiated. The fir'st of thrt^c i^ the proH^icephnlem m Jurehrain; the second and smallest poi'tion is the viesencephalon or vinJbroAn, while the third or caiidahuost portion is the rhouihencephalon. From these three primi- tive vesicles arise all of the parts in th(; adult brain. The Myelomeres. The spinal cord has also shown a tendency toward division. This, however, is incident to the development of the somites, for in the region of each pair of body segments, the spinal eoj-d Ijccomes some- what constricted. This gi\-es it the appearance of a series of long, undulat- ing indentures separated 1j>' narrow, unconstricted portions of the tube. Each one of these long consti'ictions constitutes a niyelomere. AltJiough its pres- ence may be considered as incidental to the dc\-clopment ol the somite, each myclomere has the significance of an actual segment of the neural tube. This fact is further emphasized by the bidia\'i(ir of the neural crests, which become segmented into portions corres])onding exactly with the nn'elomeres. In this light the niyelomere becomes something more than the mechanical expression of the develo])ing somite. It furnishes the basis for the conreption that tlie central axis of the nervous system is actually a segmented structure. The Encephalomeres. In the rhonibencephalic portion of tlie brain, similar divisions or segments are obser\'ed. These have been variously' esti- mated as five to nine in numljer, while in tin' mesencephalic portiim of the brain two (>r tlirei' such segments have tieen idi'ntified. The segments in the cranial portion of the neural tube have a history of deA'elopment totalh' different from those in the spinal p(jrtion, so that it seems unwarranted ti) consider these two sets of neui'al segments as homodynanious, that is, as dynainically the same. l"he bi'ain segments are called eneiphclonieres tn distinguish them finm the spinal segments or m}-i'lonjeres. Tlie encephalo- meres, although not influenced by the presence of somites, are di-pendent upon a different type of body segmentation ^^'hieh oc(airs in llie head resrion, the branchiol sr(jiii(iits. The ]:)oint which i-er|uii'es emphasis, ho\\"eA-ei-, is that the encephalomeres or brain segments are difl'ei'ent in tlieir deAclopment anil probably in theii- fimctional sigmhcance from the s])inal segments or myelo- meres. EMBKYOLOGICAL DEVELOPMENT OF TtlE NEEA'OLTS SiVSTEM directty contiguous with the neural tuhc, maiivsthe liegiiunng tlitl'ercntiation of the innermost of the menifiranes which co\'er the neui'axis, the pia mater. Increase in Size of Brain -Vesicle. Due to- the fusion of the neural folds across the niidhne, the neural groove is convei'ted mto an almost completely closed neural or eentral canal. The opemngs which it presents are formed b}' tlio several hioius in tli(.' roof-plate, as well as a wide apei-tnre at flic caudal extremity of the tube. A marked change has occurred in I he relative size of the optic evagi- nations, In the earlier stage, these vesicles were prominent; they were nearly Perineural Plexii ^■ith l.iiinlnn Central Canal Xf-iiral Tube Solid Strands of Mesenchyme Fic. 2.5. — Funuutioa of the perineural ple.xus in the 3.5 mm. albino rat eintiryu. These vascular spaces develop in the perineural meHenehyme. equal in size to the part of the brain from which thej' arose. At this stage, tile brain has gi-own much more rapidly tlian the optic evagniations. The growth which has produced this inecjuality in size has particular!)' affected tlie dorsal area of the brain-vesicle, so that the optic evaginations seem to have moved forward into a position more ventral than the one they for- merly occupied. The change in size is only apparent, however, since there IS no absolute decrease in the dimensions of the optic evaginations. Primitive Divisions of the Brain. A more important advance in this stage i-s brought about by the appearance of certain divisions m the neural tnlje. The most cephalic portion of the neuraxis now has the greatest dimen- sion. Iiniuediafel}- succeeding it is a constricted portion followed by a second 28 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM dilatation of the neural tube. In this manner the three prwiitive vesicles of the brant are differentiated. The first of these is the 'prosencephalon or forebrain; the second and smallest portion is the viescncephalon or nn'dbrain, while the third or caudalmost portion is the rhovibencephalon. From these three primi- tive vesicles arise all of the parts in the adult brain. The Myelomeres. The spinal cord has also shown a tendency toward division. This, howe^•(■r, is incident to the (jevehjjimi'nt of tin.' somites, for in the region of each pair of liody segments, the spinal cord becomes some- what constricted. This gives it tlie appearance of a sei-ies of long, undulat- ing indentures separated by narrow, unconstricted ])orfions f)f the tulie. Each one of these long constrictions constitutes a myelomere. Altliough its pres- ence may lir con.^idered as incidental to tlie development of thr somite, each myelomere has the significance of an actual segment (jf the neural tube. This fact is further emphasized by the behavior of the neui-al crests, which become segmented into portions corresponding exactly with the mA-elomeres. In this light the myelomere becomes something more than th(/ mechanical expression of the developing somite. It funiisfies the basis for tlie conception that the centi'al axis of the nervous system is actually a segmented structure. The Encephalomeres. In the rhombencephalic portion of the brain, similar divisions oi' segments are o))served. These have Ijcen variously esti- mated as five to nine in number, while in the mesencephalic portion of the brain two or three such segments have l)een identified. The segments in the ci-anial portion of the neural tufie have a histoi'y of de\'elopment totally diff'erent from those m the spinal portion, so that it seems unwarranted to consider these two sets of neural segments as homodynamous, that is, as dynamically the same. The brain segments ai'c called riicipliiilonicres to distinguish them from the spinal segments or nn-eloniei-es. The encephalo- meres, although not influenced by the presence of somites, ar(> dependent upon a different type of lnjdy segmentation whieli orcui's in the ln'ad region, the branchial segiuenty.. The point which rerpiires emphasis, however, is that the encephalomeres or bi-ain segments are diffeient in tlieii- de^-elo]iment and profiably in tlieii- funetional significance fr(.)m the s]")inal segnnaits or myelo- meres. r'HAPTER III THE EAIBRYOLOGICAL DEVELOPMENT OF THE CENTRAL NERVOUS SYSTEM (Coutnnied) THE STAGE OP TWENTT-SIX AND THIRTY SOMITES The Central Canal and Primary Flexures. Tlie principal changes ob- served at this stage result from the complete closure of the neural groove and its conversion into a central canal. This canal is relatively smaller than at any of the previous stages described, du(> to the rapid growth of the walls, the roof-plate and the floor-plate bounding it. In the cephalic portion of the neural tube, it constitutes the ventricular chambers of the Fig. 20. — Jleconstriictiou of iicunixLs of embryo of twonty- oue somites. 1. Optic vesicle. 3a. Profundus ganglion. 3. Trigeminal ganglion. 4, .Acous- tico-faeial ganglion. 8. Vestige of anterior neuropore. 14. Third ganglionic segment, 15. ]\Iesencephalon. IG. Thalamencephalon. 18. Infundibular re- gion. 20. Ganglionic. crest. 22. .interior isthmian sulcus. 23. Posterior isth- mian sulcus. 31. Preg.anglionic sr'grnent of deuterenccphal(.>n. l.Sc/i;(//e i^i ^ ■^4 if: '»f Fig -Oi'O.ss S0(_'tii)ii slio^iiig tlic iiciir:il tiilK' in a twenty-one fonnte cat emtiryo. Differentiation of the Ventral and Dorsal Gray Columns. The appear ance of the neural walls has undergone histological alteration dt'pendcnt upon a, thickening oi' the scA^eral layers of cells. The ependymal layer is still actively engaged in the karyokinelic process. The mantle layer has increased in size and shows a disposition to a rearrangement of its cellular elements. The most conspicuous among these changes is the migration of the cells in a ventral direction. iNIany of these cellular elements are becoming differen- tiated as neurocytes and long processes may be detected extending from them toward the periphery of the neural i\\]>r. This change represents the first differentiation which produces the ehaiaclrristic features of th(< nerve cell, the distinction of the sonm or Ixxlii of llie cell from its axoiic or chief con- ducting pi-oce.ss. The extension of the neuroblasts into the ventral portion of the neiii'al tube is the first step toward the formation of the ventral gran ceditnin oi the spinal cord. A sindlar migration of cells occurs in the myelen- cephalon, in the metencephalon and lo sonu^ degree in the mesencephalon; EMBRYOLOGICAL DEVELOPMENT OF THE NERVOUS SYSTEM 31 but above this level the tendency to the formation of a ventral gray column is not so distinct as in the spinal cord. The cells of the dorsal portion of thr mantle layer have migrated dorsally and thus form the beginning of the dorsal gray column. The intermediate mass of cells between the dorsal and ventral columns constitutes tlie Ijody of the gray matter of the cord. The Medullary Velum and Capillary Plexus. Surrounding the mantle layer is a thickened velum, indicating a rapid increase in the number and size of the axones which have entered into the medullary substance of the central a.xis. A rich intraneural capillary ple.xus furnishes the means of blood supply. This plexus is in direct connection with a dense, perineural plexus Fig. 28. — CrOKS section of the neuraxis in a 3.-5 mm. embryo of mus decumamis, showing the inva,sion of the mesenchyme cells into the walls of the neural tube from the perineural ple.xus. Fifi. 2'.t. — C.'ioss section of the neuraxis in an S..5 mm. embryo of mus decumanvs, showing the development of the entoneural vascular plexus at the height of its efflorescence and resulting from the confluence of individual blood spaces. situated in the inner membrane covering the cord and the brain, the pia mater. By a process of delamination, this membrane is separating from the surrounding mesenchyme, which in turn is becoming thicker preparatorj' to the formation of the dura mater. At regular intervals along the course of the spinal cord, corresponding to the position of the neuromeres, nerve fibers leave the ventral gray columns and make their way toward the m}'o- tomes. These fillers constitute the ventral roots of the spinal nerves. The Oculomotor and Trochlear Nerves. Certain of the cranial nerves have made their appearance in connection with the secondary brain vesicles. Two of these are related to the midbrain, namely the oculomotor or third FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM t. crnnial nerve and the trochlear or fourth cranial nerve. The fibers of the third nerve emerge from tlie ventral svu'faee of the neural tul)e, while those of the f(jurth nerve make their emergence from the dorsal aspect. Neither of these nerves is, at any time, in relaticm with elements con-espondin.g to the neural crest. Tliey are purely motor nerves and represent tlic imieivation of certain head segments whose subsecjuent development leads to tln' pro- duction of the extrinsic muscles of the eye-ball. The Trigeminus, Facial and Acoustic Nerves. In the region of the nii'tcnccphaldn, a large sciisury nerve is distinguished m connection with the (,'a.s-seriaii or truicmiiial qatiiilion, a ■ . structure derived from the evagina- tion which made its a);)pearance im- meiliatelj' caudal i) a pair of dorsal roots and (1) a pair of ventral roots. Tlicfec are the structural ele- ments enteruig into the formation of a typical spinal segment. The Optic Stalk and End-Vesicle. The etaginations noted iri the earlier stages have undergone considerable change. The optic evagination is now in connection with the diencephalon. It shows some modifications dependent upon the relative reduction in its proportions as compared with the forebrain. The evagination has become slightly constricted near the region of its continuity with the wall of the interbrain, while its distal por- tion is expanded to form an end-vesicle. In this stage, the optic evagination rsolated Endoneural, Blood Space inception of Endoniuinl Plexus Neural Tube Central Canal Root Ganglion Perineural Plexu Pig, 33.— Formation of the perineural and endoneural plexus in the 5.5 mm. albino rat showing the independent development of these two systems of channels. presents an end-vesicle and a proximal portion or sfn.lk which connects it with the interbrain. The eye-cup develops from the end-\'esicle out of which arise the retinal portions of the eye. Axones from retinal cells extend into the optic stalk io form the optic verve, chiasm and tract. Both the stalk and the end-vesicle retain then- original lumen; the ventricle of the interbrain at this period is in connection with a large recess in the optic evagination by means of a canal extending through the; optic' stalk. The Trigeminal and Acoustico-Facial Evaginations. The e\ aginations of the early stages marking the trigeminal and acoustico-facial nerves have 36 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM lost tlu'ir original diverticular character. They have become ganglionic masses whicli participate in the formation of the Gasserian ganglion and of the ganglia, eoiuiected respectively witli the acoustic and facial nerves. The Infundibular Evagination. Another evagination of importance has made its appearance in connection with the neural tube. This is a diverticulum which appears in the floor-plate of the forebrain at its caudal extremity, the iitfiindihulor cvmjiiuition. This evagination gives rise to the infun(hbular stalk and process. It assumes importance because it subse- Fie. 34. — 'I'run.sver.se si.-ctiuii tliroimli an i-l,ij;lil iiiillinn'tLT pig cniljr,\'u .sliuwlun tlie charac- teristics of a typical spinal segment. The neural tube with its narrow central canal occupies a central position; attached to it are the ventral and dorsal spinal roots. Each pair of dorsal roots has connected with it a pair of dorsal root ganglia. The dorsal and ventral roots fuse to form a pair of mixed nerves (motor and sensory). Each pair of mi.xed nerves divides into a primary dorsal and ventral branch. Each pair of primary ^'cntral Ijranches is connected with the syinpathetio system by a pair of rami communicantcs. queiitly conies into relation with an evagination of the moutli cavity, the oral jxickit of Rathke, from which tlie pituitary gland takes origin. The pituitary gland and infundibular process together constitute the hiipophijsis cerebri. The Otocyst. An invagination from the somatic ectoderm develops at this stage and establishes ultimate ri'lation with the nervous system. This invagination occirrs in the somatic ectoderm in the region bordering upon the metencephalon. It is at first a deep indenture in the surface which rapidly is converted into a hollow sac situated beneath the ectoderm and in contact with the neural tube. When finally converted into the oval sac, it EMBRYOLOGICAL DEVELOPMENT OF THE NERVOUS SYSTEM 37 IS known as the otocyd. It establishes relations with the seventh and eighth nerves and gives rise to the membranous internal ear, inehKling the ^cvii- circular canals and their ampulla;, the saccule, the utricle, the carudis rcuniens, the cochlea and the ductus endolymphaticus. The stage of twentj^-six somites marks the appearance of the Jive sec- ondary vesicles of the brain. It is characterized bj^ the further differentiation of the structures from which spring two imjjortant end-organs of special sense, the cijc and the ear. Myelenceplj iH Nsi Ganglion Acces ^' soriu3 1 phalon Ventral Kcgion of Erto]>(if Zone (Infundibular Region) Dorsal Uesion of r^'toptif Zone (Dienecphalon) * >ptic "N'esiele liegion of 1 • toptie Zone (leleneephalon) Fig. 35. — Reconstruction showing stage of six and one-half millimeters (thirty somites) • the secondarj' brain vesicles in fdis domcstica. It gives final evidence of the segmental character of the spuinl cord in the myelomeres and the segmented ganglionic masses, the dorsal root ganglia. It also indicates the inception of a segmental process in the brain wliich results in the formation of the encephalonieres. It contains the beginning of the process which results in the formation of the hypophysis cerebri. THE STAGE OF SEVEN AND ONE-HALF, EIGHT AND ONE-HALF, AND ELEVEN MILLIMETERS THIKTT-ONE SOMITES Aula and Hemispherium. The five sccondarj' vesicles show consider- able advance in their development. This is especially the case in the telen- cephalon which, at the stage of twenty-six somites, presented a simple extension in a dorso-ventral direction of the main body of the original pros- encephalic vesicle. It is now possible to recognize two lateral additions to this original mctlian expansion of the forebrain. The endbrain tluis consists of a median and two lateral portions. The median element is the aula. A groove upon either side separates it from the two lateral expansions which are sym- metrical and have a tendency to extend forward beyond the aula. Each of these lateral expansions constitutes the hemispherium from which each cerebral hemisphere takes its origin, while the aula contains the cephalic portion of the third ventricle and has its cephaHc limit in the lamina terminalis. 0,S FOJvAr AM) FUNCTIONS OF THE CENTRAL NEKVCJUS .SYSTEM The mesencephalon is still u lai'se vesicle separated from the dien- et'phaJ(.)n l)y (he niiiirior islliiiiiiin .^iilcii.^ and from the metencephalon Ij}' the posterior ixlliiinoii .\/ilcus. The metencephalon and ni3'elencephalon, with tlie exccjitioii of an incr(_'ase in I heir ilia.meters, show little change. The Sulcus Limitans. jV longitudinal groove divides each lateral wall of the neiu'ai tulie into a \'enli-al and a. dorsal zone. This groove is the sulcus lunitnns. The jmi-tioii of the lalcral w,\\\ venfral to the sulcus is the basal plate, wlule 1he i)ortion of the wall dorsal to it is the alar plate. The sulcus hnutans may he traced as far cephalacl as th(^ dienceplialon. The lateral walls of the neural tube show consideralde increase in their diameters, due to a rapid ac(auiiuhd.ion of neurohlasts in the basal plate, especiall}- in the region of the \'entral gi-a,\" cdlunui. In (he alai' plate, the cells an; forming the doisal gray column, and the ui1ei-nieili;i I e region between the two cohunns consti- Ductu^ Kndu Myel*Tufpli;il I...i,-ilu.|irial View For- iiiatK>ri uf Uemispliiri-- Fig. 3(i. — Itt'unnsLniclinn sliowiiiK .^ta^c of spvcn and mu'-lialf jnillimclc)>> (tliirt>'-onc seinili's) in f'l'-s dor/irslici. tutes the body form the two columns in the gray matter is not appareid. Histologics ll\', the cells collected in the basal plate are distinctly larger than those assembled in the alar plate. This is regarded as evidence of a process of motor different iati(.)n in the region ventral to the sulcus limitans and of sensoiT differentiation dors;d to it. Formation of the Membranes. The mesenchyme which surrounds tlie neural tube' has undergone fui-ther differentiation and it is possible to dis- EMBIiYOLOGICAL DEVELOPMENT OF THE NERVOUS SYSTEM 39 tinguish three connective tissue coverings surrounding the cord, the yia mater, the innermost; the dura mater, the outerniost and the arachnoid, interposed between them. Each of these membranes appears to be a definite lamination of the paraxial mesoderm. Between the dura mater and the arach- noid there is a considerable space which has the appearance of containing fluid. This is the subdural space. An even greater interval exists between the inner surface of the arachnoid and the pia mater. This is the subarachnoid space, in which is containeil th(^ cerebrospinal fluid. A condensation of the mesenchj'me has been carried to the point where it is possible to identify the protovertebrcB or the primitive vertebral bodies. These are laid down in car- tilage; and contain in their center the remnant of the notocliord. Lateral to the neural tube are the pedicular and laminar processes of the vertebra.. At regular intervals between these pedicles and laminue are the interverte- MrtrnLcplialnn Dui tus r iidi>l\ nipbdti u .\triuiii ]Myek;iici-i)ha]-inphati Inception nf Semi- L'iriul:ir Canal.s Myelencepluilu rf^Ienrrf.halon Xa.sal Ectoderm Xn Ml and Alll < 'rciplia rjDX Fia. 38. — Recoiistnie-tiijii .slniwing ,sta(;i' uf eleven millimeters mfrlis itomeslica. mater and the arachnoid. They are lodged in special evaginations formed by the two inner coverings which invest them loosely. The iieiipheT-al arms of axones from the dorsal root ganglion ct'lls may be traced into the mesen- chyme, and some of them e.xtend as far as the cutis plate of the somite. This outgrowth of nerve filjers indicates the means by which the future derma- tomes or skin segments of thi' bo(ly are iiuieivated. The Formation of the Sympathetic Ganglia. A change of imjiortancc involving the dorsal root ganglia occurs in a migration of ganglionic neuro- blasts into the loose mesenchyme ventral to the prutovertelirte. This migra- tion extends inward and forward toward the median line. Immediately dorsal to tlie aorta and at regular intervals along its cijurse, collections of neuroblasts assume the form and arrangement of prevcrtrhral qaiigJia. These structures ultimately are arranged as two pi-evertebral chains of gangha situated dorsal to the aoi-ta. This is the beginning of tlie sijnipailictic EMBRYOLOGICAL DEVELOPMENT OF THE JCEra'OrS SYSTEM 41 system and represents the inception of the ganglionated sympathetic cord. The cells which have migrated to form the prevertebral ganglia do not sever their connection with the dorsal root ganglia. They maintain an attacliment to the dorsal root fibers Ijj^ means of slender liimdles of nerve filaments which constitute the rami communicantes. The s}'mpathetic system dev-;'lops as an accessorj- to the central axis fjut retains its connec- tions by means of these communicating branches. The Hypophysis and Otocyst. The infundibular evagination has in- creased in size and is in contact with a corresponding evagination from tlu^ mouth cavitj', Rathke's poclajt. Tlie two arc not only in contact but have fused, thus forming the hypophysis cerebri. The infundibular evagination gives rise to the neural portion of that structure, while the evagination from the mouth cavity forms the glandular portion. The otocyst also has undcr- JMcsenccphalon N in Metenccpli Lion Ductus endoh iii- phaticus Lon;iif.udinal Diencephalon Myelenrcphaluu Semicircular canals ! assenan Oanglion (N v) Telencephalon N IX Oropharynx Optic Vesicle Fig. 39.— Reconstruction .showing stage uf twelve and one-halt millimeters in /cKs doviestica. gone further differentiation. In addition to the simple oval sac first devel- oped, it has produced a lateral divcrticuhun situated close to the neural wall. This is the ductus endolymphaticus. The original portion of the otocyst is known as the atrium.. STAGE OF TWELVE AND OXE-H,\LF, FOURTEEX, SFA-ENTEEX AND TWEXTY-SIX MILLIMETERS The Telencephalon. In these comparativeh' late stages of embryonic development, all of the definitive elements of the nervous system are laid down, and further changes in them depend solely upon expansion and growth. A notable difference in the relations of the two portions of the telencephalon, the hemispherium and the aula, is the fact that the hemi- spheres have Ijecome the predominant structures and have completely 42 I'flllM AND I'lrXCTrONS OF THK CKNTKAL NEia'Ors S^'.STEM concealed both the aula, and tlie dienceijlialou. Suhsequent chanK<'H in tlie brain are dominated \>y tliis r;i])i(l growth of the lieinis])liei'<:s which, al- though the latest eleinent.s to api^ear, become the largest structures of the encephalon. The Diencephalon. The walls of llic diencephalon ha^'c become thick- ened, and it is possible to recognizr in thcni Ihe sululivisioiis of the thalamus and the hypothalamus. The floor-iJatc of the mterbi'ain shows no change except the elongation of the; optic nerve and the migration of thi; eye cup awaj' from the brain. The end-vesicle, Ijy a process of invagination, has formed a two-layered optic vesicle with a conca\'e fundus. The infundibular evagina- tion has been surrounded Ijy Ilathke's pocket and the neural portion of the hypophj'sis is almost completely invested by the ectodermal cells forming the glandular portion of that organ. The oral (.'vagination of the pituitary N III Dit'iirrpirMon M I n Ductus En 1 l\ II pli t yeini Fit:. 40. — Ddisal cord of chick embryo at 5th day of incubation. {Cajal.) A. B — Motor cells. C — Ventral roots. D — Dorsal roots. E — Dor.sal coluruiis. a — Superficial white sub stance, b — Commissural fibres. grated into tliis ventral position, their axones begin to tra^'erse the mantle layer, penetrate the marginal hiyer, and finally emerge from the neuraxis as the ventral roots. A still greater degree of migration is seen in the cells wliich form the alar plate. Tliis migration gives rise not only to the tlorsal gray column of the spinal cord and honrologous areas in the bz-ain-stem, but some of these neuroblasts proceed still further to form the neural crest. In this structure differentiation is carried on l.)y which some of the neurocytes Ijecome sym- pathicoblasts ami tithers gniiglioblasts. The sympathicoblasts in their turn undergo further migraticm, leaving the neural crest to form the prevertebral EMBRYOLOGICAL DEVELOPMENT OF THE XEKVOVS SYSTEM 49 /A Fig. 47.— Epitlielium of tlie i;ord in cluck embryo at .5th day of incubation. Golgi's method. [Cajol.) .4.— Ephithelial flask. B— Epithelium of the dorsal groove. C— Branched fibers in the:ventral r-olumn. ganglia of the ganglionated cord of the sympathetic system. The ganghocytes of the neural crest become differentiated to form the dorsal root ganglia of the cerebrospinal nerves. In this process the neuroblasts pass into the neurocj'te stage by a marked increase in their cytoplasm. Their nucleus is retained in the center of the cell. The soma gives off a single proto- plasmic process which be- comes bifurcated to form a central and a peripheral branch. The neurofibrils appear in the cytoplasmic process of the cell simul- taneously with this bifurca- tion. In this manner the sensory elements of the peripheral nerves and dorsal root fibers are differentiated. Fic 4S. — Sketch of the motor roots in the lumbar cord in an embryo of a duck at the 70th hour of incubation. Silver nitrate reduction. (Cajal.) A — Spina] cord. B — Perimedullary space. C — Meningeal men)brane. D — Cone of growth of motor nerve fiber. E. F — Cones in perimedullary space. G — Cone migrating toward the dorsal region, a, b — Stationary cones. c,H — Cones travelling in the antero-posterior direction under the basal membrane, e — Motor nerve fiber. CHAPTEIi, IV THE UNIT OF STRUCTURE OF THE NERVOUS SYSTEM THE NEKVE CELL OR XEITRONE Adaptation to the Purposes of Generating and Conducting Nerve Im- pulses. Tlic nianncr in which a mcrhanism opo'ates to accoinphsh its pur- |joscs (.li'|)(_'ii(ls ii|")(iii the coiistituciits wliich ciitiT into its stnii'tiirt.'. I'lie (jpe'fatidlis (li thr lii'r\'(ius syslciii ;ii'c made |iiissililc I ly the prfsciicc oi two (iistiiict sul)st;uiccs, one, the irli/lc iiiiiilir, which is conipi'iscd (if nerve fibers, the other, tlie (//''(// iiinllcr, inadi' up nf ncr\'e cells. In a iien(:'i'al sense the wliite ni:itter plays ilie i'elati\'i'ly passive part in tlie coniluclicin nt nerve impulses, while (he ,<2;ray matter is much more actively engaged in ihe genera- tion or I ransinissioii of tliese impulsi's. There is a tliird element in tlie ner- vous system, the iiinrdijlia. which serves as a supporting and protective substance. Although the gra>' and wliite substances appear to lie different in kind, the>- are in fact pari of the same essential tissue constituting tlie nervous system. The gray matter is made up (if the liodies of cells wliose conducting processes, the a.xones, constitute the \vliile matter. Fi'om this fact it is a])pa- rent that the unit of structure of the nei'\'ous system is tlie nerve cell or neurone, m which two main diA-isions ina\' be disi inguished, the cell hexli/ or isonui, and the eell processes. Cerlain features of tjie nei'\-e cell cause i( to stand out among the other cells in the organism. I'efoic considering its foi'iu and characteristics, however, it will lie a(K'anlageiius io wow the neurone as a living organ, taking into account its purposes and the mannei' in which it achieves its ends. As a. living oi'gan, the nei'\'e cell carries on the complex chemical acti\'i- ties in\-(il\'e(l in its melabolic processes and designed to regulate the assimi- lation of nu(i'iti\-e matei'ial brought Io il by the (arculation. In a word, the neurone has its chemical |)i'oblems to meet and is e(|uipiie(l with the proper mechanism for this piii|)(ise. Nerve cells are c(inslan(l\' generating, I'cceiving or storing up ner\'e impulsi's. Il is unforlunale lliat we do iiol knoft' Ihe exad character of such impulses. Whethei' ihey ai'e chemical oi eleclrical or a comtunation of both, is a (|ueslion wliicli has not yet been detinitely answered. In a few is("ilated instances, it is known that the>'are electrical in (heir nature. Such, foi' example, are (he impulses generated by the electric organ in the medulla of the elec- trir torpeilo. .\nother fund ion of (he nerve cell is the deli\'(>ry or transmission of im- piulses which it generates, receives or stores up. This cellular actn'hy retiuires the existence of a special apparatus. .50 UNIT OF STRUCTURE OF THE NERVOUS SYSTEM 51 STRrCTURE OF THE XEUROXE In view of these faets it may bo assumed that the nerve cell not only presents many of the characteristic structures of other cells m the horly but IS also provided with special mechanisms for the performance of its own special functions. The Cell Membrane. In the first place, to set it apart from all other elements as a hvmg organism the nerve cell is possessed of an essential membrane, in which respect it resembles other cells. This membrane limits .7— Mr rf — Disc n mvelin. Fiii. 40. — Cell of the cerebro-clectric lobe of (lie toipedo. (Cajnl.) rnlirnno, slisrlitly se]>:iratr(l from the prntoplasni. h — Conni-rtinL' link r — CollatrTal n^r^'r■ branch. f union or lirik in the constriction of Ranvicr. c — Constrn tcil nmon of axone unpro\-ided ^ith the cytoplasm and seems to be a peripheral condensation of the protoplasm which serves to contain the cellular elements. The membrane is often more complex than a mere peiipheral concentration of C}'toplasm: it iiiaA' lie con- verted into an actual entlothelio-conjunctival capsule. This is the case in the essential membrane of the ilorsal root ganglion and sympathetic cells. The cell in the electric organ of the medulla otilongata in torpedo shows the same kind of highly specialized limiting membrane, which probabh' serves as an insulation from adjacent cells in the electric lobe. Pecuhar pericellular FOiai AXU FUNCTIONS OF THE C'ENTKAL NERVOUS SYSTEM not.s have been identified in the cell membrane, concerning the nature and siKiiificance of which ditt'c-rent views have l>een expressed. These pericellular nets have been considered essrntial for the conduction of impulses from cell to ci;ll. Provision for this function, liowever, seems to be made in a more ample and better way. According to Cajal, the nets represent focal regions of greater density and concentration in the periphei'V of the cj'topktsm constituting the essential membrane. The Cytoplasm. The second dement in the nerve cell is its cytoplasm, that is, all of its pi'otoplasm excei)t that tilling the nucleus. This cell plasm is made up of a fibrillar network called the vpongiuplasm or adi.romahc net. It lodges a chromadc or ilee])ly slainiiig sufislance and is distributed through- FiG. 50. — Short a.xis cylinder cells ul tlic brain; adult cat. Ehrlich's method, {('ajul. ) a — Pericellular network. C — Spiny proeeascs. b — Con denaation of network at (.lendritie origin. I'll.:. .J I. — Cell of the ^langlioiiated chain of the earth worm. Silver nitrate reduction. (Cajal.) A — Intraprotoplaaniic eanala of Holm[iren- Golyi. /)' — Nucleus, a — Protoplasmic process. out the entire cell, inchiding the single, most highly specialized process, the iiiiplii.nldtioii cone. In the meshes of Ihis network is the cytoplasmic fluid or hi/iiloplasiii which serves as the medium of chemical exchange in the cell, while the spongioplasm serves as a flelicate, internal scaffolding. Intracytoplasmic Canals. Another important set of organs in the neurone are the Holmgren-Golgi canals, which form a complex apparatus throughout the cytoplasm. These canals are brought out t.iy means of silver impregnation and present the appearance of an actual net. They are re- garded by some authorities as intracytoplasmic lymph channels which are in connection with pericellular Ijnnph spaces surrounding the neurone. The canals are not peculiar to nerve cells Ijut have a wide distribution among UNIT OF STRUCTURE OF THE NERVOUS SYSTEM 53 the cells of the body, in vertebrates as well as in nn-ertebrates. In the cells of the intestinal tract of the earthworm, these canals are found imme- diately beneath the hmiting membrane. In vertebrates, theu- relation is usually circumnuclear, that is, surrounding the nucleus and extending to the periphery by means of minute branches which connect with the pericellular lymph spaces. These three parts of the nerve cell provide the support for its structure, the medium of exchange for its metabolism, and it may be, the circulatory apparatus for its nutrition. Chromophilic Substances— Nissl's Bodies. Another feature of the cytoplasm of the neurone is the chromophilic siihsfnnce or granules. These Fig. 52. — Intraprotoplasmic tubular network in the different ner\-e cells of the spinal cord of a dog, eight days old. Reduced by silver nitrate method. (Cajal.) A — Large funicular cell. B, C, D — Small funicular ceUs. granules stain with basic anilin ch'^cs and are known as the NissVs bodies or tigroid bodies. They vary considerably in form and dimensions, some being irregular masses, others spherical or ovoid. In size they measure from 1 to 10 micra. The arrangement and disposition of the chromophilic granules vary in different cells according to their functional activities. It is pos.sible by this criterion to recognize the functional type to which a cell belongs. Nerve cells are classified in several waj's, but one of the most significant is that based upon the disposition of the chromophilic granules. Four different types of neurones are thus distinguished : (1) the stichochromes; (2) the ark.yochromes; (3) the gryochromes, and (4) the perichromes. The principal feature of the stichochrome cells is the irregular form of their Nissl's bodies, which are arranged more or less evenly in rows. They vary in size from 1 to 4 micra, and are found scattered throughout the cytoplasm of the soma, of the bifurcation cones and of the dendrites. Stichochrome cells almost invariably have a motor function; they appear 54 Foiar and rrxcxiONS of the (;kntkal NEiu'ors system ill tliL' ventral columns of the si)in;J coi-d, in tln' motor nuclei of the bulb, pons and miill_)rain, m Deitcr's nui'lcus, in the lielz cells of the motor cortex, and the cells of Purkinje ni tlie cerebellum. Upon histological examination, the Nissl's bodies of these ci'lls aiipear to be non-homogeneous. Ill the arhiiodiromv cells, the Nissl's Ijodies ai-e arranged in a network. The best illustration of this type of nerve cell is fouml in tlie central cochlear nucleus. The iiriiochroiiir cclh present no specihc arrangement of the Nissl's bodies, which are scattered throughout the cyto])lasm in an irregular manner. This variety' is typified by the cells m (lie spinal ganglia and in the root ganglia ol' 1he cranial nerves. In 1lie pencil rotne cells, the Nissl's boiliesare ai'ranged in rows immediafejy beneal h tile cell niem- liraiie. Such cells are found in the ganglion haiienulie, in the mole- cular layer >• icpiiidiiction in the central nervous system is not possible. Many of the organs of , ^ a nerve cell arc nuich tlie '-" ■' J same as tliose found in ■ . I, i ►iw^^^' ^vt)ical cells elsewhei'e in J\ ti 1/ Ij ilif liody; indeed, if it had Fi.i. ,:,;.— IJifiVrrnt i\-p.- (if iiurln in i,i-r\-r au.l iii-u- 'i" further speciahzation roglial cells uf ;i lal.Mt. X is^^,^ inetliud, [Cajal.) than tfie features alread}' .1-Two aspects of tin ,mrl,.„.nr 111,. i.rurotHial r.dl3, a— S)H,u;i„t. jiotcd, it WOulcl be difficult the superior surface ol llir iiiirlcus h~>\\'>\\\nii, its cross .sci-f i^n e-Xu.l..us ,,f a jiranul,. r,.!l ,,f tl,.. rrr,.b,,llu.n. />-Xucl,.„,, of a fVj,. i],, nourone tO CarrV pyranii<:lal 'ell ol thr brniii L — Nui'liais ol a iiiotor ci-Il of the cori.l on its fund ions. It re- mains to be seen in '\\'hat details the nerve cell difft^i's from the lypieal cell in order I hat ft fifa\' fill its special offices. Form of the Nerve Cell. In f(.>rnt, the neurone is highly s])e(aalized. It nfa>' 1)1' i)\-ramidal, l)yri- foriif, globular, stellate or fu-^ffoi'iii. It" diticrs friiif; 1.\']ncal cells in thai three ''^V'?'" different parts fiia\' be re- \'^&i\ cognized in it. These are; \\''t»:-^i (1) the siiitm or the cell body; (2) the ilmi/nlrs or prntciplii.^iii /(■ jii'iict's,\rs; Co) the axoiic or ncurolVii'iUnr jiroccss. ^rhese parts, either in their usual appearance f)r in some modific.at ion of it, are cliarfictcrist ic of all nerve cells, ddie soma, varies much in size atid form. Its coiistit uents ha\"e ;ilread\' lieeu descrilied, as well as it s ty]"ies, ;tccnrdtng to fis dtlferent fiinct ions. The Dendrites. The ihaidiates are the proto- phfsmic pl'ocesses ol the cell. Idicy form a series of more or less thick branches which extend out from the soma. The dendrite has a trunk and an end-afborization. The trunk di\-ides dichotomoiisly until its br.anchmg has gi\-en rise to a dense end- brush. lOach dendrite has upon its braitches a numl)er of minute qlohidar budics, known as (jcnninilcs, Kpines or raricosilics. They :ire regarded bv some a ralilut. t'le. r,S—y\,,Un- cell ,,f tlie spinal renl Xissl'.s iiictlHMl. If 'iijnl.) 'I — Axis f.yliiulcr. I, — t'lLrniiiatic mass. . S noii"in|)lasni i!- Xurlnis, t— llifiiri.alioii ronr, " UXIT (JF STRUCTURE OF THE NERVOUS SYSTEM 59 4, size, ace J syiiai")tic jiinc- ">., 4t:m^ observers as artifacts, but the majority of authorities consider them the contact points m tlie synaptic junction Ijetween one cell and another The trunk of the dcnihite tapers sli-htly as it passes away from the soma. The number of .len.hites connected with each cell vaiies from one to ten. The dendrites ma>- be identified ]>y their relativclv kn-e size. The axone is the slender process of the cell and may extend a great distance from its bodv, while the di'iidrites nc^vei- pass outside of the gray matter. All s tions for this reason aw performed in the gray suljstance. The constituents of the dendrit(:' are the same as those of the soma, that is to say, cytoplasm, spongioplasm and hyaloi^lasm, the chromophilic substance, the tubular apparatus of Holmgrcn-Golgi and the neurofibrillar network. In the larger branches and trunk of each dendrite the Nissl's bodies are prominent ele- ments. At the point of bifurcation of the trunk into the fii-st branches, there is usually a large Kissl's body marking what is known as the bifurcation cone. In the smaller dendritic branches, the Nissl's Ijodies become progressively less in size and have the appearance of fine chromophilic flecks scattered through- out the protoplasmic sul.)stance. The Axone. An important dis- tinguishing characteristic of the nerve cell is its axone. This, unlike the dentlrites which are protoplasmic, is distinctly a neurofilM-illar process, and in reality contains but few of the ele- ments constituting the cytoplasm of the soma. In contrast to the dendrites I'^ig. 59. — Ciiant cell of the infrriui- part which ai'(> somotipetal the axone, m re- "f ^■'"' ""'"" ammoms of a ralif.it I , ,, • 1 1 ■ 1 -i I i Mctlioil of Ehrlich-Bethe. {('uinl.i garcl to the iminilses which it cr)n(hicts, , . ,, , ^ ,, ,,.,,,, _ ' ^7 — Axis-* ylindor. c — CcllLiteral (!n-idiii'_' into is soinatiftKinl. It is to Ije itlentified bv '"'t'"^'' branciies, ./— \'arirusitips ...i tiir ,i,,ii- its form, size, relations and constituents. The axone through most of its course is a cylindrical tulx'. Certain portions of it, however, may not be described as tubular ami these exceptions will l^e mentioned later. In length the axone varies from a few millimeters to many centimeters. iShort axones are found in cells whose somatifugal process never leaves the gra}' matter. These are known as cells of Golgi type II. Cells with long axones often send their somatifugal process through a distance extending from the Betz cells of the motor cortex of the lirain to the lumljar region of the spinal cord. Those cells wliich send their axones through 60 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM the white substance of the central nervous system or into the peripheral nerves are known as cells of Golgi type I. The transverse diameters of axone.'i differ according to the amount of myelin sheath which has been secreted as a tubular investment upon the neurofibrils. A cross section of the spinal cord will show the axone as a central rod made up of compact neurofilirils surrounded liy a ligliter, hoiriogcneous encasement, the myelin sheath. Qh) The axonal divisions distinguish the axone from the dendritic processes. First among these divisions is the implantation cone or (txone hill, through which the neurofibrils pass to enter the axone. This appears as a specialized portion of the soma and is distinguished bj' the fact that the cytoplasm here is drvoid of Nissl's Ijodies. Difl'erentiation between the trunks of dendrites and the Ix'ginning of the axone is easilj' made by this means. At the base of the implanta- tion cone and extending for some distance into the C3'to- plasm of the soma, all chromophilic elements are drawn inward antl the plasm has a clear homo- gcnetius appearance. The axone liill is usually shorter than i\\v dendritic trunk, and as it proceeds away from tlie cell ljod\' il gradually tapers. At the apex of the vow, th(- cytoplasmic substance of the cell disappears and the axone is hcM'i' nothing more than a fascicular collection of the neurofibrils surrounded by perifibrillar substance. This, the second division of the axone, characterized by the absence of protoplasmic covering, is known as the axone cervix or neck. Its length is variable and depends upon the position of the nerve cell from which the axone arises. If this cell is situated, deep in the gray matter the ax()U(; cervix may be long. As a rule the axone arises directly from the cell body in what may be called the axonal pole. There are, however, certain exceptions to this rule, as in the case of some of the gronulc cells in the granular laijer of the cerelxdlar Fig. go. — Purkiiije cell »( tin- liuiiian brain. Golgi's metliod. (Cajal.) — .\sis cylin'lrT. b — Collateral braach. r, d — Spaces arnoiii thi^ protoplasifuc hranflies for the stellate cells. UxNIT OP STRUCTURE OF THE NERVOUS SYSTEM 61 cortex in which the axone may take origin from one of the dendritic procesHcs. The third division of the axone ls identified by tlie fact that the neuro- fibrils have acqmred an outer covering, the mvehn sheath, which is re- garded as a secretion of the neuroglial cells. Tins slieath is maintained from the point of its first acquisition by the neurofibrils until they ap- Fio. 62. — Details of the spines on the protoplasmic processes of the Purkinje cells. Ehrlioh's method. (Cajal.) -1 — Dendrite with gemules. B — Iligli power of same, a — Dendrite. proach their end-arborization. After tlie axone has received its myelin sheath, it is known as the axis cylinder. 61. — P5'ramidal cells of the cerebral cortex of a guinea-pig, showing the spines of the protoplasmic processes. Ehrlioh's method of methylin blue. (Cajal.) a — Two medium pyramidal cells, b — Collateral spines of a protoplasmic trunk belonging to a giant pyramidal cell, c — Axis cylinders, d — Basilar branches mth their spines, e — Collateral branches of the protoplasmic trunk with their spines. Fig. 6y. — End-baskets of Held en- veloping the cells of the nucleus of the trapezoid body in an adult cat. (Cajal.) a — ^';^l■llOlc3. /' — Terniinal fiber. The fourth division of the axone is represented by its branches. These are of two classes; the collaterals, which are generally given off at right angles to the course of the axone, and the end-branches, which are devoid of the myelin sheath, since this covering disappears at the point where the axone begins to break up into its end-arborization. The end-branches are studded with many fine gemmules or varicosities in the same way as are the branches of the dendrites. Thev are not all of the same character, but vary consider- 62 FORM AND FUNCTIONS OF THE <.'ENTRAL NERVOUS SYSTEM ably ill form. In man}' instances rich cnd-arljorizations may Ijf observed in a profuse branchiuK of the neurofibrils. Another type is found in the end- bdnkets u} Held, and still other types are the terminal hutlons and terminal eriel- nets. The a.xone varies in its constituents throughout its several tlivisions. Its fundamental elements are the neuro- fibrils, and these may be found from one end of the axone to the other. The implantation cone or axone hill is made up of these neurofilirils surrounded In' tlie cytoplasm of the cell in which, how- ever, tliere are no massesof chromophilic sultstarice. The axone cervix consists of neurohliiils, the cytoi)]asni of the cell being entireh' alisent: a |)erifil>rillar substance alcme surrounds tlie fibrils. The axis cylinder consists of a central core iif neurdfibi'ijs, its accompanying ]i('rifibrillar substance and a myelin sheath which is a lipoiil or alliumino- adipose sufistance. thought ):>}' many to lie secreted by the netu'oglial cells. This is true of the axis cylinder as it is found in the central nervous system, but in the jieriphei'al nei'ves the tufmlar sheath sui'riiunding tlie neurofilirils contains othei- sti'uctui'es which will bedescrilted 11 the discussion of tlie ]ieripheral nerves. At more oi' less irregular in- ter\-a]s along the course of the axis c>-linders as they make Iheii' way tlirougli the white matter of tlie crnti'al nervous system, tJK.'l'e occur eertaill riodidar bodies known as the nodes of Tiiiireni-Lciiraff. These are most com- mon at the |ioint of axone bifurcation, and dift'er from the nodes of Rarnder f in the jieripheral ner^-es in that, ac- coi'ding to C'ajal, they poss<\ss (wo discs instead of ijnc. The existence of a neurilemma, or sheath of Schwann, such as has been described in connection with the peripheral nerves, has lieeii denied in the axis cylinders of the central nervous system. It may, however, exist as an Fill. 64. — l'\i:iiniil:il ri'll (.r the liraiii a rabbit. Golgi's methoij. (Cnjnl.) a — B.isilar protoplasmic braiirlics, ^ — Di'Tiilrilic trunk and its branche.s. c — Collaterals oi axis- cylinder, e — Long axis cylinder. I — The white njatter. P — Dendritic arijorization. L'NIT OF STRUCTURE OF THE NERVOUS SYSTEM 63 extremely. fine outer covering of thv. myelin shciitl]. The incisures of Sclimidt- Lantermann, such characteristic features of the peripheral nerves, are not encountered in the axis cylinders of the central nervous sj'stem. THE NEUROCtLIA Derived from the ectoderm, as are the neurocytes, a second type of cell is found in the central nervous system. This is the n(>uroglia which forms a supporting and protective tissue. The neuroglia is made up of cells hav- ing the general characteristics of other cells in the body. Such cells present a cytoplasm containing fine granulations irregularh' distributed throughout the body of the cell and extending into the proximal portions of the principal appendages. A second element is represented bj- a large number of radiating fibers connected with the cell and extending in all directions from it. Each neuroglial cell has a relatively large nucleus limited by a well-defined achromatic membrane; it contains chromatin particles and one or two nucleoli. A small body situated in the cj'toplasm is generally regarded as the centrosome. The neuroglial cell, being less highly differen- tiated than the nerve cell, seems to retain a potentiality common to most somatic cells, in that it is able to reiirockice itself. Types of Neuroglia. There are twf) princijial varieties of neuroglial cells, those situated in the white matter amt those in the gray mattcT. The neuz'Oglial cells of tlie white matter are characterized b>' their long fibers. The cell body is 6 to 11 micra in diameter and is in connecton with twenty to forty fiber prolongations. Not all of these prolongations are of the same size or character. In general, the fibers of the neuroglia in the wliite matter may be classed in three groups: 1. Filaments of a moderate fineness and relatively short. 2. Filaments which are fine but extend for a great distance away from the cell l)ody. 3. The so-called vascular appendages of the neuroglial cells which are comparatively thick filaments with clublied ends, the latter adhering to the endothelium of the capillary vessels in the neighborhood of the cell. The neuroglial fibers of the white matter form more or less complete fibrous envelopes for the axis cylinders and the Idood vessels, while at their distal extremities, they become confluent imc with another and in tins way form a reticular limiting membrane around the outer surface iif the n(-uraxis, the siibpiaJ neuroglial inonlirauc, tiioiilnruKi liiiritnns ijlur. The neuroglial cells in the gray matter differ fi-om those in the white mat- ter chiefly in that their fiber processes are shortei', more branching and give the whole cell a mossy appearance. Several varieties of the neuroglial cell are recognized in the gray matter: 1. Perimsculnr Cells. These elements have a triangular or irregular body, the surface of wliich is m contact with a capillaiy, in this way rein- forcing the capillar^- wall. 2 Pediculated CelU. This form of neuroglia possessi-s a short or long pedicle which is simple or branched and which by its ..xtremity is implanted 64 FOiai AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM upon the wall of a capillary, ha-\'iiig in this regard much the same purpose as the perivascular cell. 3. Independent Stellate Cells. This is the most common type; they present a large number of filaments extending from them in all directions. They do not seem to conie in contact with blood vessels. 4. Caudate Cells. These neuroglial elements are found in the first layer of the cerebral cortex, and in addition to presenting many branched pro- cesses, have several streaming prolongations like the tail of a comet. For Fig. 1)5. — Nuuroglial culls of the white substance of the human ijraui. \\'eigert'3 method for neuroglia. (Cajal.) A — Cell body. B — Longitudinal section of a capillary. C — Cress section of another capillary, a — Slender neuroglial fibril, b — Unstained protoplasm. this reason thcj^ are also sometimes ctiUcd cometarij cells. The long, tail-like process extends to the pia mater and in conjunction with similar processes from other neuroglial cells participates in the formation of ii siibpiaJ neuroglial limiting membrane. 5. Cells tvith Bifurcated Fibers. These elements are found in the cortex of the cerebellum and are marked by the absence of any fiber processes except one or two long extensions which usually bifurcate close to the cell and then extend for a long distance from it. Each of these processes is studded with small varicosities and terminates in the outer limit of the cerebellar cortex, where its extremity is engaged in the formation of a subpial neuroglial limiting membrane. ITNIT OF STRUCTURE OF THE NERVOUS SYSTEM 65 6. Pericellular Cells. Neuroglial cells of this type are observed in con- nection with many of the larger neurocytes throughout the nervous system. The number of such cells surrounding a neurocyte may be three, four or even six, a large number of them usually being found in connection with the pyra- midal cells of the motor cortex of the brain. Not infrequently they lie in relation to the beginning of the axone, particularly that part which is free of myelin, the axone neck. Physiological Significance of the Neuroglia. The physiological signi- ficance of the neuroglial cells is not fully understood. Some of their offices are obvious, while others must still be left to the disclosures of further investigation. That the glial cells form an effectual sup- porting tissue for the nerve elements, a scaffolding for the nerve cells and the axis Fig. 66. — Neuroglial cells of the gray sub- stance of an adult human brain. Golgi's method. {Cajal.) .4— Independent cells. B— Cell with vascular pedicle. ('—Perivascular cell. F— Capillary vessel. Fig. 67. — Neuroglial cells of the white substance; brain of an adult man. Slow method of Golgi. (Cajal) cylinder processes, seems to be without question. By their extensive processes passing to the periphery of the neuraxis, they give rise to a limiting mem- brane which, although mcomplete, none the less effectively provides a re- ticulated structure covering the surface of the spinal cord and bram. A smular internal limiting membrane is developed m relation witli the ven- tricles of the bram during the developmental stages prior to tlie disappear- ance of the central canal in the spinal cord. The older idea that the neuroglial cells were m some way C'onnected with the processes of providing nutrition for the nerve cehs, principally becau,se of 5 66 FORM AND FUNCTIONS OF THE CENTRAL NERVOI'S SYSTEM their intimate connection witli the blood vessels, seems untenable in the light of our present knowledge. It is not possible to explain their existence on the grounds that they serve to fill the wide spaces caused by the expan- sion of the neuraxis or to obliterate the cavities produced in the neural tissues when the nerve cells undergo a process of degeneration. ]Many reasons appear to sustain the view that the neuroglia, especially in the gray matter^ serves as a tissue element for purposes of insulation, separating one neurone from another and thus preventing undesirable or perhaps harmful contacts between the nerve cells. This interpretation is not applicable, how- FiG. 68. — Neuroglial cells of the white substance of the brain in an adult man. Slow method of Golgi. (Cajal.) A — FlattPDed perivascular neuroglia] cell. B — Neuroglial cell with long branches- C — Pedieiilated neuroglial cells. D — Capillary vessel o — Pedicle attached to the vascular endothelium, r — Long branches which bend at contact with the vessel to form its perivascular adventitial membrane, d — Bifurcated pedicle. / — Smooth and very lont: processes, j; — Thin and short processes. ever, to the neurogha in the white substance. The view advanced by Andrei- zen concerning these cells has something to recommend it. It is his belief that by virtue of its resistance and elasticitj', the neuroglia is able to protect llie nerve cells from the \'ascular pulsations of neighboring vessels. The marked reaction of the neuroglia against pathological processes going on in the central nervous system, and more particularly those processes which come as a result of toxemia, infection and trauma, nuist not be over- looked. The rapid prolifc^ration oi' the neuroghal cells seems to inthcate that tliey, like certain fixed and wandeiing tissue cells of the liody, are capa- Lile of protective response against threatened or actual in\-asion. This UNIT OF STRUCTURE OF THE NERVOUS SYSTEM 67 proliferation of neuroglial cells, known as gliosis, is so common a manifesta- tion in diseases of the nervous system as to give rise to the belief that neu- roglial cells themselves are possessed of a phagocj^tic power, or else that they are capable of creating a barrier for the purpose of limiting the extension of any disease process affecting the brain or spinal cord. In certain inflamma- tory processes, such for example as acute anterior poliomyelitis, some of the cellular elements engaged in the process of removing the necrotic ven- tral column cells have been identified as ameboid glial cells. In this light the phagocytic activity of at least some of the neuroghal cells cannot be doubted. PATHOLOGICAL SYNDROMES OF THE NERVE CELL By syndrome is usually meant a combination of symptoms resulting from some disturbance in the body. In the sense in which this term is applied here it has reference to a combination of pathologi- cal changes which may occur in the living nerve cell as the result of some disease. Two major patho- logical syndromes are re- cognized in neurocytes ^^^^ ec,._Two antenor horn motor cells of the cord of a namely, the syndrome of j,^^,_,^^j^ j^^ ^^.j^^^h the large sciatic had been cut primary degeneration and fifteen daj-s previously. Nissl's method. (Cojnl) ttici Qimrfroinp of '^ecoridxir'}! A — Cells whose chromatic substance is disintegrated and whose LUe iyiiaiOlliV OJ anvunuu, y ^^^.|^^g jg eccentric. B— Cell in more advanced chromatolysis: nr Wnllcrinn deaprieration n — A.xone. b — Small chromatin masses. < — Chromatin dust. or yy auerian aeytlieiuuon. .j,j^g^,,,_,^jj^^ji„^^^ainson!yin the dendrites and in the neighborhood 1 The Syndrome of of the nucleu.-;, where it is condensed in a homogenous mass: the ^ cellular membrane is evaginated by the nucleus. Primary Neuronal De- generation. The changes in the appearance of the cells ai'c the result of some injurious influence exerted directly and primarily upon the nerve cells themselves. These changes are caused by poisons or by unfavorable physical conditions. They may be occasioned by certain inorganic substances or produced by micro-organisms, such for example as acute anterior polio- myelitis, tetanus and rabies. They may be the result of inanition, of anemia or hyperemia. On the other hand, the determming cause may be physical, such as exposure to extremes of heat and cold. The most conspicuous change in the nerve cell in primary degeneration is the solution of the Nissl's bodies which begin rapidly to break down and disappear This process is known as chromatolysis. It begins around the periphery of the cell and rapidly extends toward the nucleus. Ultimately 68 FORM AND FUNCTIONS OF THE CENTRAL NERVOl^S SYSTEM all tlio Nissl's bodies (tisap])cai', not only from the protoplasmic processes of the cell but from its soma as well. The second change is seen in a swellinR or edema of tlie cytoplasm of the cell. The cell Ix'gins to chaiij;-)' its form and finally, tin account of the swelling, it becomes more or h^ss globular. The essential memltrane appears attenuated as a result of the cellular edema. The nucleus also becom(.'S swollen and, ceasing to occupj' its centric position, moves out to the periphery, where it is in contact with the essential membrane, wdiich may ultimately rupture. The nucleus is then extrudedfrom the cell. Fig. 70. — Cells of the cord of a rabbit with rabies. Silver nitrate reduction. (Cajal.) A — Normal cell. B — Neurone where tlie neurofibrils appear in the form of filaments. C — Cell where the transformation of the neurofibrils into filaments eoniniences. a — Axone. b — Perinuclear neurofibrils. A marked change is noted in the relations and conditions of the neuro- fibrils. Individually tlicy seem to liecijuie liypertrophied and thickened. The rich neurofiljnllar net disa]")];)ears. The filirils pass through the cells as con- spicuous strands. Ultimately they break up into fragments and disappear. Wlien the neurone reaches this stage of degeneration, there occurs a marked reaction m the ni.airoglial cells, particularly tliose of the pericellular type. These cells undergo rapid proliferation and almost com])leteh' surround the diseased neuroc\-tes. If th(' affected ner\-e cell does not ultimately succumli, its constituents begin to reestal>lish themselves in the reverse order of the primarjr involve- meiif. Xissl's bodies begin to reap)ie:ir, the nucleus resumes its central posi- tion, the neurofilirillar netwi.irk makes its appearance and the increase of neuroglial cells no l(.)nger exists. When this is the case, a protiess of regenera- UNIT OF STRUCTURE OF THE NERVOUS SYSTEM 69 tion is accomplished, the neurofibrils, in consequence of their reappearance in the coll body, soon begin to grow out into the axone and the nerve cell finally reestablishes its connections. 2. The Syndrome of Secondary or Wallerian Degeneration. This syndrome is the result of injury or disease, not of the cell directly but of its chief process, the axone. The lesion may be at some distance from the cell body or relatively near to it. In this latter event, marked changes occur in the cell secondarj- to the axonal disturbance. These alterations are in many waj'S similar to those alreadj' described in primar)' degeneration. There is, however, a conspicuous difference in the reactions within the cell bodj^ The Nissl's bodies disappear by a process of chromatolysis, although in this case the solution Ijegins in those bodies immediately j) about the nucleus and ex- tends peripherally toward the essential membrane of the cell. The cj^toplasm, the nucleus, and the neurofibrils react in a manner similar to that already described in primary degeneration, while the axone, peripheral to the lesion, undergoes a series of changes which will be dis- cussed in detail in considering the nerve fibers Fig. 71. ell. d- Two spinal ganglion cells of an old man. Osmic acid coloration. (Cajal.) Large pifrment granules, b — Smaller granules, c — Satellite Site of origin of the axis cylinder. GENERAL SUMMARY OF THE NEURONE A review of the general features of the neurone indicates that it has many elements in common with the somatic cell. 1. It possesses an essential, limitmg membrane, a eijtoplasm, a nudevs with chromatin bodies and several nucleoli, but it is entirely devoid of a cen- trosome. This latter fact deprives it of the possibihties of reproduction. 2. The organs constituting its cytoplasm are designed for two distinct purposes. First, cellular metabolism, and second, the conducticjn of nerve impulses. 3. The cellular organs pertaining to metabolism, are: the cytoplasmic framework, the cytoplasmic fluid, the tubular apparatus of Holmgren-Golgi, the chromophilic substance or Nissl's bodies, the pigmentary concretions and the fuchsinophile granulations. 4. The organs which provide for the conduction of nerve impulses are the neurofibrillar network and the perifibrillar substance. 5 The neurone, like other cells of the body, possesses a soma or body, but unlike most other cells, it is equipped with certain processes which are 70 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM of two varieties, the dendrites or protoplasmic processes and the axone or neurofibrillar process. 6. The neurone is possessed of a dynamic polarization, that is to say, the impulses which come to it make their entrance into the soma bj^ way of the dendrites and leave the cell by way of the axone. 7. The dendrites or protoplasmic processes of the neurone are confined to the gray matter of the central nervous system or else to the gray matter forming ganglia. The axones may confine themselves entirely to the gray matter but a vast number of them pass beyond this limit and, becoming collected in a dense fascicular mass, constitute the medullary substance of the central nervous sj'^stem and the peripheral nerves. 8. Nerve cells which send their axones into the white matter of the central nervous system or into the peripheral nerves are known as Golgi type I. The neurones whose axones never leave the gray matter are known as Golgi type II. 9. Each nerve cell, comprised of its three major parts, the soma, the dendrites and the axone, constitutes a morphologically and physiologically independent unit, the neurone. CHAPTER V THE INTEGRATION OF THE NEURONES TO FORM THE NERVOUS SYSTEM THE NEURONE THEORY The Manner in which Nerve Cells Establish Intercommunications. For the purpose of generating nerve impulses and conducting them through the nervous system, it is essential that myriads of nerve cells be brought into relation with one another. The means by which neurones are connected and the manner in which a number of such cells, although widely separated, may be mutually engaged in the performance of a common function, is the fundamental problem concerning the organization of the nervous system. Before it is possible to consider the means of intercellular communication or what maj'' more properly be termed neurone integration, it will be neces- sary to have a clear idea of the various types of cells whose differences in form impose upon them differences in the means of communication. In general, intercellular communication is accomplished by cell processes, that is, by the dendrites and the axones. Nerve cells show such variations in this regard that the following groups may be distinguished: Cells Encountered in the Nervous System, Classified with Reference to their Means of Intercellular Communication. I. Cells having a somatifugal process only. 1. Cells with relatively short prolongations and without myelin sheaths; cells of the retina and of the olfactory bulb. 2. Cells with long prolongations (interstitial gland cells, intestinal sympathetic cells). 3. Cells with long prolongations and with myelin sheaths (unipolar cells of the mesencephalic nucleus of the fifth nerve). II. Cells with processes for receiving and dispatching nerve impulses (somatipetal and somatifugal). 1. Sensory cells provided with one receiving process and one axone (unipolar olfactory cells, cells of the retina, ganglion spirale (cochlear), ganglion of Scarpa (vestibular), dorsal root ganglionic cells connected with the spinal cord and the cranial nerves. 2. Cells provided with several receiving processes and one long axone (motor cells of the cord and brain stem, most of the cells of the cerebral cortex, sympathetic cells, association and projection system cells of the central nervous system). 3 Cells provided with several protoplasmic processes, that is, den- drites and a short axone (cells of Golgi type II, cells of the cerebellum, and many cells in the cerebral hemisphere). 71 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM ■1. Cells proviiled with several dendrites and one long axone which divides to continue as several collaterals in the white matter of the central nervous sj^stem (tautomeric and hetoromeric intersegmental and intrasegmental cells having a T-shaped axone found in the cerebellum, in the spinal cord and in the brain). Dynamic Polarization. The dendrite conveys the nerve impulse toward the cell Ijody, while the axone serves to carry it away from the cell body to some destination more or less distant. Thus, two nerve cells might serve the purpose of conducting a nerve impulse in such a way as to permit passage from the first cell by its axone to the dendrites of the second cell. This simple mode of conduction from cell to cell does not hold good in all cases, since thei'e are many cells which possess no somati])eTal dendrites. Some other means of establishing com- iiumication lietween such cells must be em- ployed. In still other instances nerve cells are provided with bifurcated axoncs and a specializcfl tvpe of intercellular com- munication is necessary for them. Defer- ring until later the consideration of these exceptions, the details of the intercellular communication which is most common in the central nervous system may be con- sidered. This depends vipori the somati- petal conduction (jf iminilses by way of the dendrites and the somatifugal conduc- tion by way of the axone, a mode of trans- mission which constitutes the basis for the hiw of (hjnnmic pojnriiation in the neurone. The nerve impulse leaving a multipolar cell passes by way of the axone to the dendritic end-brush of the next cell that it is designed to influence. On approach- ing this Ijrusli, the axone bi'caks up into interlacing terminal arborizations. How conduction is established at this critical point of junction has been a matter of debate for a long period. The Neurone Theory. In view of the embryological investigations of His, and the histological studies of Cajal, Waldeyer in 1S91 formulated the theory of intercellular communication which to-day is generally accepted. According to this interpretation, each neurone is an independent unit. It establishes connection with another neurone not by continuity but by con- tiguity of its neurofibrils. This conception of the unity of neurones and their communication by means of the contact of their processes is known as the neurone theory. In this manjier nerve cells may be arranged in chains and groups of correlated chains, thus constructing special sj-stems for the per- formance of definite functions. The neurone theory has not, however, gone unassailed. Held in 1897 Fig. 72. — Cereliello-rubro-spino- effcctor pathwa}'. THE INTEGRATION OF THE NEURONES 73 contended that there is a direct protoplasmic continuity from one nerve cell to the next by moans of pericellular nets about the neurone and its dendrites. Apathy in 1897 also gave assent to the idea of cellular continuity on the grounds of his investigations upon invertebrates. It is his conception that there are two tjq^es of structures in the nervous sj^stem, i.e., those which produce conduction, the neurofibrils, and those which produce nerve im- pulses. Bethe in 1897, although he could not agree with Apathy as to these two types of structures, expressed the belief that the nervous system, by reason of an anastomotic network, maintains a complete continuance through its neurofibrils. Yet in spite of these objections, the neurone theory is still held by the concensus of opinion. It is particularly supported by the fact that the de- generative changes in the nervous S3'stem, due to any cause whatsoever, are usually limited to the neurone system immedi- ately affected and do not spread to adjacent sys- tems of neurones. Contact Continuity — Synapsis. The critical point of contact by means of which nerve impulses are propagated from one neurone to the next is called the synapse, or synapsis. Dependent upon the form and type of the cells, several varieties of synapsis may be observed: 1 . The Axosomatic Synapse. In this type the end-brush of the axone terminates about the cell body. This type of synapse occurs in the Purkinje cells of the cerebellum, in the ganglion habenulse, in the olfactory bulb, in the mtestmal sympathetic cells and the unipolar cells of the mesencephahc nucleus of the fifth nerve. 2 The Axodendritic Synapse. There are several forms of this type of intercellular communication: (a.) Primary axodendritic synapse, in which the articulation between one cell and the next is accomplished by the axone brush entwining itself about the protoplasmic trunks of the dendrite. These are known as cUmhmg fibers. They occur in the Purkinje cells of the cere- bellum in Deiter's nucleus and in the protoplasmic processes of the red nucleus in the midbrain. (6.) Terminal axodendritic sy^iapse, m which the end-brushes of the axone come in contact with the fine protoplasmic pro- cesses of the dendrite, as for example, in the cruciform contact found m the Fig. 73. -Centrifugal fibers in the retina of birds. Method of Ehrlich-Bethe. (Cajal.) jl — Nerve fiber. B — Cell surrounded by arborization, a, b, c — Varicose end fibrils. 74 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM motor cortex, in the cells of Purkinje and in the motor cells. A third variety of terminal axodendritic synapse is described in which there is a parallel arrangement of the contact processes. The contact connections of this variety are to be found in the glomeruli of the olfactory bulb, in the synapsis of the rod cells and the external nuclear layer of the retina. Interpretation of the Centralization of the Nervous System. The neurone theory offers a satisfactory explanation of the mode of integration in the different parts of the nervous system. It does little, however, to make Fiii. 74 — .Ascending end arliorization, human rcrel a — Ascending Hl>er. /' — Purkinje cell. Method of Co.x. {Cajal.) clear the process which led to such a complex organization so placed as to become the central controlling organ of the body. The necessity for this centralization of the nervous system is unques- tionably to be found in the evolution of animal motion, by means of which the living animal makes its adaptation to the environment. If the environ- ment is simple, little adaptation is needed and motion is correspondingly simple. Where the adaptation is of this kind, the motion may involve a single limited part of th(> body. The entire reaction, beginning with the receipt of the stimulus which is to elicit the motor response and ending with the trans- formation of the stimulus into contractile activity, may be carried on bv a THE INTEGRATION OF THE NEURONES 75 mechanism mtrinsic to a single part. When the environment is more com- plex or the animal is able to deal with a simple environnient in a more varied manner, much greater requirements are made upon it in the way of adapta- tion, and the combinations of motions become more complicated. Such would be the case in an animal whose adaptive reactions require the cooperation of several aUied parts of the body. The interaction of these parts would be dependent upon a coordinated controlling mechanism, since such regulation of motion could not be left to a diffuse and scattered set of organs. During rvx, Fig. 75. — Basket cell of the cerebellum of a white mouse. (Cajal.) '■1 — Purkinje cell shaded with osmic acid. B — Basket cell, o, h — Pericellular nerve ramifications forming baskets, c — .\xis cylinder. the process of the evolution of motion, Cajal recognizes five epochs through which centralized control has passed. 1. The Epoch of Irrit.\bility. During this period, a stimulus re- ceived by the surface of the animal is transmitted to a part closely adjacent to that in which it arose, and so affects certain contractile structures as to produce a limited, immediate movement. No intermediate tissue is needed for this conduction, because the transmission of the stimulus is made direct from the area receiving it to the contractile elements of that same area. It may even be that there is no intermediate step in the transmission of the impulse, but that it falls at once upon the tissue which is to respond by con- traction. This kind of motor adaptation will, of course, be expected of very lowly animals whose necessities in adaptation are slight. It is the kind of reaction which is witnessed in the motor functions of the Porifera or sponges, for here the reaction to an afferent impulse is confined to a very limited portion of the cellular organism. It would be impossible for such an animal to carry on extensive coordinated actions or be capable of performances which serve the purposes of complex ends. It is sufficient that the motor re- sponse should be Hmited, for in a general way the animal is composed of more 76 PTJRM AND FUNUTIONS OF THE CENTRAL NERVOUS SYSTEM or less independent unit-structures each one of which can carry on its own existence. In any event, no great amount of coordinated action is required, and its method of response is, therefore, relatively simple. 2. The Epoch of the Reflex Arc. A significant step forward is taken when the stage is reached in which several parts of the body may be made to participate in response to a single stimulus. Such is the case when a stimulus is received by the receptor A and at once transmitted to the more or less in- dependent effectors B, C and D, which at once go into action as a result of the impulse transmitted to them from the receptor .1. This reaction re- ciuires the introduction of an intenuediate element, for the reason that too many obstacles would stand in the way and too great a dispersion of energy Fig. 76. — Diagrams showing the ailvantage of the multiphcatioii of the neurones and of their grouping in central gangha. (Cajal.) A — Imaginary invertebrate in which it is supposed only cutaneous or sensory neurones exist [a). B — Invertebrate, possibly a sea-anemone, in which the two kinds uf neurones already exist, motor (r) and sensory uij, but are not yet centralized in ganglia. C — Invertebrate, of the worm species, in which motor neurones (c) are concentrated in ganglia, a — Sensory or cutaneous neurone, b — Muscle, c — Victor neurone. would result were the hnpulse to be transmitted directh' from one cell to another until all of the parts designed to jjarticipate in the reaction had been properly stimulated. The evolution of this intermediary element resulted in the appearance of ih.e fundaments of the nervous s,ystom. It was effected by the specialization of cells so differentiated that they were capable not only of receiving impulses but of transmitting them as well. The cells specialized to receive the impulses became the receptor system. The cells differentiated to transmit the hnpulses received antl produce a motor response constitute the effedfjr system, while the conjunction between these two systems establishes the reflex nrc. With the development of this refle.x arc to operate in the control of motion, tiie connection by means of .sjmapsis between the receptor and effector cells affords the simjjlest illustration of the neurone theory. Certain of the invertebrates furnish examples of the epoch of the reflex arc, such as the Celonterates (the sea anemone and corals). In these animals, the affer- ent stimulus is diffusely retroflexive by a spread of the impulse from a limited area of reception to an extensive area of reaction through a reflex arc. In contra.st to these forms, the sponges typify a discretely reflex action of tht; afferent stimuli, which are received from a relativel,y small region and determine a response in a correspondingl}^ small area of action. THE INTEGRATION OF THE NEURONES 77 3. The Epoch of the Intersegmental Reflex Neurone. Anijnal luotioii could not increase in its complexity and multiply the ability with which it was able to deal with the increasing variety in the environment, unless the many parts which were to participate in the motor reactions became more specifically adapted. There are reasons to believe that the segmented type of body structure lends itself more readily to greater com- plexity of animal motion than body structure of other types. When the body became segmented, therefore, the nervous system reflected this segmental character in segments of its own. Each segment controlled a definite territory which it brought into cooperative activity with other territories and parts. This result was accomplished by the development of neurones which con- D. S. Fig. 77. — Diagrams showing the economy resulting from the fusion of a double chain in invertebrates into a single chain. The transverse commissures, necessarily long in the double chain, D, are shortened in the single chain, S. {Cajal.) a — Crossed motor neurone, h — Commissural neurone or sensory association neurone, c — Sensory fiber coming from thie slcin. d — Longitudinal commissure, e — Nerve composed of centrifugal motor and centripetal sensory fibers, f — Transverse commissure. nected one segment of the nervous system with several others, the inter- segmental reflex neurones. 4. The Epoch of the Suprasegmental Reflex Neurone. The next advance was marked by the addition of another group of n(.'urones which were not strictly confined to the segmented portion of the nervous sj'stem. The}' constituted a structure which made its appearance in re.'^ponse to new demands for more extensive neural control and more complex combina- tions of motion. Prior to this epoch, the reflex arc antl the intersegmental reflex neurone sufficed to regulate the motor reactions in the behavior of the animal. In the first place, all of the motions during this period wore imme- diate responses, that is to say, reflex actions in the strict sense which were represented by the translation of sensory stimuh into motor impulses with- out appreciable delay. This fact in itself serves to explain the character of the resultant behavior whose limited scope and stereotyped form imparted 78 FORM AND FUXCTIOXS OF THE CENTRAL NERVOUS SYSTEM to all of its rcac'tions a pronounced inflexijjility. Unrlfi' given circumstances one set of rear'tions, and one set only, could be expected as the result of given stimuli. Furthermore, the combinations of these stereotyped per- formances are themselves limited in their scope and rigid in their form. Since these reactions are dependent upon the coordination of several seg- ments of the body, economy of space and material would require that their controlling elenients should not be separated l>y great distances from each other, but should be brought together in some centralized position, such as that occupied by the nervous system. These influences have played an important role in the process of centralization. When, however, it became necessary to extend the scope and form of behavior by in- creasing the motor perfor- mances which entered into it, another element was requisite for controlling organs of the body. The need was not so much for a complication in the combination of possible motions, as it was for the specific adaptation of motions to more complex purposes. The essential element in this adaptation was the factor of time. Heretofore there was no a p p r e c i a b 1 e i n t e r v a 1 between the receipt of a stimulus and the dispatching of the motor mipulse, so that the reflex act was an immediate Fig. 78. — Scheme of the progressive centrah- zation of the sensory cells in an animal series. (Cajal.) A — .Sensory neurones of the earth-worm. B — Sensory cells of a mollusk, C — Sensory cell of a vertebrate. consummation in motion. (Jftentimes this very rapidity of discharge would defeat the accomplishment of some higher purpose, for a delay of even a fraction of a second might eventuate in determining circumstances more advantageous to the animal's activities. Tliis pause in the reflex reaction time, this period of latency, furnished an interval for reflection, as it were, in which a selection between alternatives might be made and the one, proven liy experience to Ire the nK)st advantageous, might be chosen to guide the resulting acts. This would be the first step in introducing a more plastic type of behavioral reaction. The new element which jiroduced the period of latenc_y l\v holding in check tlie res])onse until the most favoralile moment had arrivi.'fl would, in its essential nature, provide the important factor of inhibitidii. The nervous system, wlien this epoch was reached, had come under the guidance of a new influence and acfiuired the far-reaching quality THE INTEGRATION OF THE NEURONES 79 by which it is able to withhold action until it is most opportune and profit- able. In this sense, behavior is no longer a matter of instantaneous impulse, but is made subject to a certain simple degree of supervisional review, guided by a primitive form of judgment which may be taken to mark the beginning of the psychic life. If centralization became necessary in the epoch of the intersegmental reflex neurone, it was now even more essential, for reasons both of economy in space and of time in conduction, that the controlling organs should occupy a central position. Thus from the earliest epoch there have been urgent reasons for the concentration of neui-al control in a central sj'stem. 5. The Epoch of the Psycho-Assocta- TioxAL Neurone. The final step in the centralization of the nervous mechanism, enabling it to attain the consummation of its functional capability, arrived with the addition of the psycho-associational neurone. By this means numerous associa- tions are made possible between the various types of sensibility, including somesthetic sense, vision, hearing, taste and smell, out of which the experience of the individual is constructed and upon which the foundations of the higher faculties rest. The Essential Relation of the Receptors to the Effectors. The underlying, universal principle throughout this entire process of evolution has been the maintenance of an adequate relation between the receptors and effectors of the body, together with the constant expansion of the functional poten- tialities of this relation. In other words, the more broadly and deeply an animal senses its environment by means of its afferent sensory mechanism, the more ex- tensively and satisfactorily it reacts by means of its effector mechanism. The ani- mal recognizes the labile character of its environment through its receptors and is able to make its tion to ever-changing conditions by its effectors. Fig. 79. — Diagram of the course of an impulse in a sensory cell of the mammalian spinal ganglion. (Cajal.) yl— Body. B — Trunk, C — Central branch, thin, acting as axis cylinder and coursing toward the cord. V — Peripheral hiranch, thick, performing the f unction of prolonging the protoplasm and bring- ing the current from the periphery. E — Fiber furnishing the pericellular arbori- zation to the body of the ganglion cell. M — Spinal cord. F — Skin. The course is indicated by the direction of the arrows. accommoda- THE RECEPTORS The fundamental condition observed in the epoch of surface irritabihty, in which the receptors and effectors are practically in one and the same tissue, has been retained during the process of evolution. Although there has come about a great separation in space between the receptors and the so FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM effectors, and an intermediary agent — the nervous system — has developed between them, it is stih the essential relation between the structures which receive the impulses and those which translate them into motions that char- acterizes the nature of the nervous mechanism through all of the epochs which have been described. The classification of the receptors is as follows: (1) Exteroceptors, those receiving organs which have developed in the ectodermal covering of the Fig. so. — Plexus in the cornea in a raljbit. Ehrlich'.s method. {Cajal.) \ — Framework of fundamciita] plexus. B — Sub-busal iiloxus. C — Interepitholial end branchr..s. J) — ^Subepiiiielial end branches. bod\-. (2) ProprioccjdorK, those receiving organs which have developed particularly in the mesoderm and more especially in relation to the muscles, joints and bones. (3j Intcroccptors, tliose receiving organs wliich have de- velo]ied in the entoderm, especially in connection with the viscera. Exteroceptors. A great variety of exteroceptors have Ijeen identified in the ectodermal covering of the lx)dy. Tliese fall into two large groups, ( 1 ) the contact receptors, and (2) the distance receptors. Contact Receptors. Two varieties of contact receptors are distin- guished, namely, those situaterl in the epidermis, the cpidenrial or intni- epiiermi,! receptors, and those situated in the dermis, the dermal receptors. THE INTEGRATION OF THE NEURONES 81 Epidermal Receptors. There are several types of these epidermal receptors: 1. Receptors in the Cornea. The arrangement of the end-organ m this structure is that of a series of plexus, consisting of a deep fundamental plexus of coarse fibers, situated beneath the epithelial structures, and a fine subbasal plexus. From this layer is derived a still finer subepithelial plexus which gives rise to the intra-epidermal terminations of free fibers between the cells of the cornea, or fibrils with varicosities upon them. Fk , 81. — Terminations of nerves in the anterior epitlielium ot the cornea in an adult rabbit. Gold chloride method. The minutest nerve fibers are seen coursing between the epithelial cells and ending in varicosities on the corneal surface. (Cajal.) Fig. 82. — Ivy-hke (hederaceous) terminations in the interpapillary prolongations of the skin on the finger of a several days old infant. Reduced by silver nitrate method. (Cajal.) A. — .\fferent fibnr. a — Reticular end dilatations situated bonoath the epithelial cells. 2. Receptors in the Epithelial Portion of the Skin. The sensory apparatus here consists of a dense subepithelial plexus from which arise numerous branching neurofibrils to form a rich arborization occupying an intra- epithelial position. These end-fibrils either terminate freely among the epithelial cells of the skin or become specialized to form the tactile meniscus or disc of Merkel. These discs are disseminated, ovoid corpuscles, con- sisting of epithelial cells which stain more deeply than the adjacent elements. Beneath these cells are concavo-convex discs of neurofibrils devoid of their myelin sheaths. 3. Receptors in the Ectodermal Mucous Membrane. The sensory appara- tus of the mucosa in regions where the cellular arrangement is cylindrical or columnar, is furnished by varicose neurofibrils and terminal buttons, while in stratified and pavement epithelia, the fibrils form nets with free branching, intra-epithehal, varicose terminations. 4. Receptors about the Hairs. The sensory end organs with which hairs 82 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM are equipped are of two classes. The ordinary non-cavernous hair is inner- vated by two independent sets of nerve fibrils. One of thf;se consists of cir- cular fibrils which terminate in buttons or reticular nets. The other is a set of ascending fibrils which terminate about the vitreous tunic. The cavernous hairs, such as the vibrissae, are innervated by a series of circular neurofibrils about the cavernous sheath and also by ascending fibrils in and about this Fio. 8.3. — Terminations of nerves in the skin of the paw of a cat 4 days old. Golgi's method. (Cajal.) A — Horny epidermis. B — Malphigian layer. C — Deep part of Malphigian layer sprinkled with grains of pigment, a — l.arge nerve trunks, b^ — Collateral fibers. ': — End arborizaticm. (/ — Terminal ends situated between the epithelial cells. sheath. All of these fibers lose their myelin coverings before they terminate and then end either as a tactile meniscus aliout the vitreous tunic or as free varicose endings in the same position. Dermal Receptors. The second large group of contact receptors is situated in the dermis. These are the dermal receptors. The>' present them- selves as a variety of end-organs having highly specialized forms. They are less diffuse than the epidermal receptors, and are for the most part encapsulated. Physiologically, they depend for their reaction upon some degree of pressure upon the epidermal surface. 1. The Corpuscles of Grand ry-Merhel. These end-organs are found in the submucosa of the tongue and mouth. Each corpuscle consists of an outer conjunctivo-endothelial sheath which is continuous with the sheath of Henle of the ner^-e. Enclosed within this sheath arc two voluminous epithelial c(tlls more or less hemis]iherical in shape and op]iosed to each other by a flat or concave surface. Between these opposed surfaces is a biconvex disc continuous with the end of the neurofibrils. The corpuscles of Grandrj'-Merkel may be simple or compound. When simple they are made up of a single neurofibril ending between the two epithelial cells. THE INTEGRATION OP THE NEURONES 83 When compound, several neurofibrillar endings maj- be invested by epithe- lial cells and included in a single conjunctivo-endothelial sheath. 2. Tactile Corpuscles of Meissner. These end-organs are found in the tips of the fingers and toes, in the skin over the lips, in the mammae and the external genitalia. Thej^ occup}^ the summit of the dermal papillae which, for this reason, are known as the neural papillce of the skin. They are so placed that their long axis is perpendicular to the skin surface. They are ovoid in form, but may be tuberous or lobulated. Their size varies from 30 to 50 micra in length and 20 to 30 micra in thickness. These corpuscles usually alternate in the skin with the vascular papillce. The corpuscle of Meissner consists of a thick, fibrous capsule, a granular central substance and a terminal arborization of neurofibrils, constituting a rich spiral reticulum which tends to taper as it approaches the summit of the end-organ. The capsule of the corpuscle of Meissner is rich in cells, although it is relatively thin. 3. Corpiiscles of Krause. These end-organs present a simple and a complex type. The simple form of the cor- puscle of Krause, the end- bulb, has been considered by authorities as a corpuscle of P^^ ^^ -Lo.g.tudmal ^"'fon of a tactUe hair of a T, • ■ ■ -x X J J rat. {Fcno.) Pacmi in its most reduced ^_j,^^„„,, ,„„j^,„,ti,,3, , heath. ^-Annular siBus. C-Cav- nnd dim n]pqt form Tt consists emous portion of the vascular sheath. D— Region of the nerve ana SimpieSlIOlXn. ll. CUn&l.^l.s ^^^^^ /—internal conjunctival sheath. F— Superior dilatation. of fl fibrous structure resemb- O —Afferent nerve fibers. H— Free arborizations /— Epithelial 01 a nOlOUS btlUeouiL ie»t-iiiu gn^.eiope /—Superior constriction Kith the series of the cut tactile lins; the corpuscle of INIeisSner memscuses. A'-Annular protuberance. i-The hair. M-Inf error ^ ^ . constriction. and also contains a portion of the sheath of Henle which extends from the nerve fiber. In addition, there is a central granular mass which is cylindrical m form and has a rounded extremitv. In the midst of this granular mass is a neurofibril of the termination. The complex type of Krause s corpuscle resembles in many nerve ways the corpuscle of Meissner except that it is enclosed in a much thicker sheath, is more spherical in form and contains a richer plexiform arrange- 84 FORM AND FUNCTIONS OP THE CENTRAL NERVOUS SYSTEM fl^ Fig. Sfi. — Two corpuscles of Krausc in the conjvinctiva. Ehrlicli's method. (Cajnl.) A — Simple type in eonjunrtiva of an o\. B — Complex type in eonjuneti\-a of man. 86. — (.'(iipiiscle of Mcissuer in the human skhi. (.Cajal.) A, Afferent sensory fiber, a, End buttr)n situated under the epiderniis, h, Termination of ttie branches of neurofibrils. /■ X n 1 'i'^ l''n;. 87.— -NfU've tenninatioiis in the anterior p(.)rti()n of a cat's tongue. Ehrlieh's method. (Cajal.) A — Hont>- rpithelium. B — M"ali:ihip;ian body, a — Subepithelial nerve fasciculus, b — Tjranch on the way to a lingual papilla, c— liitra-epidernial fibrils. -/ — Lingual papilla. THE INTEGRATION OF THE NEURONES 85 ^':-v Fig. S8. — Genital corpuscle in tlie human glans penis. Method of Ehrlich. (Cajal) T^NcTve fibers. 6 — Capsule, c — End arbo- rization. uient of neurofiljrils within the central granular mas.s. Both forms of the cor- puscles of Krause are found in the con- junctiva and in the skin of the external genitalia. A highly complex form of Krause's corpuscle identified in the mucous membrane of the external genitalia is described as the genital corpuscle of Dogiel. 4. Corpuscles of Pacini. These end- organs arc the largest of those encountered in connection with the skin. The,y are ovoid in form, vary from 1 to 2 milli- meters in length and are scattered throughout the suljcutaneous tissues. In the pulp of the fingers they are en- countered in greatest number. They are also found upon the course of nerves, in figaments, in interosseous membranes, in the perimysiiuu and endomysium of muscles, in the naesentervand mesocolon. They are composed of a granular central bulb made up of a series of concentric capsules. These capsules consist of con- nective tissue laminiB separated from one another by lymphatic spaces and con- taining manj' endothelial cells. In the Fig. so. — Nci-ve terminations in tlie border oi a duck's tongue. .Silver nitrate re- duction. (Cajal.) ■i — Corpuscles of Herbst. B — .Simple corpusele of .Merliel. C — Another rorpuscle of Merliel supplied with two terminal discs, a and b — Bulbous termination of nervc> fiber. r~Epithelial eel' Fig. 90. — Corpuscle of Pacini in the human skin. Gold chloride meth- od. (Cajal.) n — Sheath of Henle of the afferent fiber. h — Central granular substance, c — Capsules. -■ 86 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM center of this Imlb-like structure is a single tenninal jieurofihril surrounded by granular suljstance. This laminated Imlljous organ is the most common Fig. 91. — Corpuscles of Timofocw, pro.static capsule of a dog. Ehrlich's method. {Cajal.) A — I^arpe fiber in continuation with tiie axial trunk of the corpuscle. B — Minute fiber, ramifying around dhe granular substance (after Timofecwl. Fio. '.)'2. — Details of tlie ncuroHlitillary framework in the granule cells and arborizations of the mossy tibers in an adult cat. .Silver nitrate reduction. (Cajal.) a — Principal trunk of the mossy fiber, h — Loops and terminal plexuses, c, 'I — Complex loops, e — Twinings in tlie form of a figure S. A — Protoplasmic process. B — Body of the cell. form of the corpuscle of Pacini. There are, however, se^'eral varieties of the Pacinian body, such as the iirgaiia aj Hcrhst. These structures consist of a single central neurofibril surruundetl l.ty a large granular mass with a thin, conjunctivo-endothehal capsule. The organs of Golgi-Mazzoni are also THE INTEGRATION OF THE NEURONES 87 small Pacinian bodies found at the junction of tendons with their muscles. The}' arc long, cylindrical structures enveloped in a well defined capsule. Fig. 93. — Tactile meniscuses produced by a solitary nerve fiber in a rat. {Cajal.) A^Division of the fiber. B — Constriction of the brandies. C, E — End enlargements sfiowing the dis- position of the neurofibrils. D — Enlargements at the points of division. 5. The Corpuscles of Timofeew. These end-organs are a specialized form of the Pacinian body. They are found in the submucosa of the membranous and prostatic portions of the urethra and in the prostatic capsule. The cor- puscle is a long, ovoid body with a conjunctivo-endothelial capsule made up of concentric layers. It contains a large mass of central granular material and is penetrated by two neurofibrils, in which detail it differs from the corpuscles of Pacini. Distance Receptors. This group of receptors is represented by a series of speciahzed end-organs which receive impressions borne to them through air or through air and water. Distance Receptors for Smell. These end-organs are stimulated by aro- matic and volatile substances which act upon the speciahzed olfactory mucous membrane of the nose. The peripheral organ of smell consists of an epithelium containing sensory cells which give rise to the fibers forming the olfactory nerve. These cells are bipolar. Their central processes enter into the formation of the fila olfactoria, while their peripheral processes are equipped, at their extremities, with a number of hair-like prolongations, the olfactory hairs. Distance Receptors for Vision. The visual end-organ is in the retina. It is capable of response to stimuh of a series of vibrations ranging between 400,000,000,000 and 800,000,000,000 per second. Distance Receptors for Hearing. The end-organ of hearing is responsive to air vibration whose frequency ranges from .30 to 30,000 per second. The actual receptor is the spiral organ of Corti situated in the cochlea of the internal ear. ss rORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Proprioceptors. The proprioceptors are usually classified in two groups, (1) the sensory end-organs in the muscles and tendons, and (2) the spe- ciahzed end-organs of the vestibular portion of the internal ear. Sensory End-Organs in the Muscles and Tendons. The Muscle Spindles of Kiihne. These end-organs are found in striated muscles scat- tered among the muscular fibers. Each of these end-organs consists of a capsule containing a central gray substance, in the midst of which are the unmyelinized neurofibrils forming a rich terminal arborization. The Musculo'Tendinous End-Organs. Four general varieties of such end-organs are recog- nized: (\) The muscido-tcndinous terminations; these are known as the musculo-tendinous end- organs of Golgi. They are placed at the junction of a tendon with the muscular fibers and are found only in such nmscles as have great im- portance or great strength, as for example the calf-muscles in man, and the muscles of the eye. They consist of a thin, conjunctivo-endothehal envelope, a considerable mass of central gray matter in which ramify the terminal branches of the neurofibrils. Functionalh', they serve for the musculo-tendinous sense and are essential to the orientation and control of motor a,ctivities. (2) The corpuscles of Golgi-Mazzoni have already l.)een described as a variety of the Pacinian bodies situated in the musculo-tendinous appa- ratus. (3) The terminations of Sachs and ReAlet Fig. 9 4 . — Musculo-tcnd- of reptiles and amphibia are considered rudimen- inous organ of Golgi, i.^y-y forms of the corpuscles of Golgi situated adult cat. Gold chloride method. (Cajal.) a — End-arborization, b fiber. c— Terminal branches jjiance to the musculo-tendinous corpusclcs of of the end-arbonzatjon. e — JNluscu- ... lar fibers. GolgL They are distinguished, howevei', by their topograph}', for they do not appear in the tendons but in the subcutaneous tissue, in the aponeuroses and the nitermuscular fascial planes. E.HD-OrGANS in the VESTIBUL.tR PORTION OF THE INTERNAL EaR. These end-organs consist of a highly specialized group of receptors con- nected with the semicircular canals, the utricle ami saccule, of the in- ternal ear. Their special function is concerned in the maintenance of equilibrium. They receive impulses transmitted to them hy the en- dolymph contained in the membranous semicircular canals, utricle and saccule. between the fasciculi of the tendons. (4) The Kiervo. terntinations of Ruffini have a distinct resem- mches -Muscu- THE INTEGRATION OF THE NEURONES 89 Interoceptors. The interocoptors are the end-organs for visceral sensibility and are divisible into two groups: (1) General visceral receptors, which are but little speciahzed organs, innervated through the sympathetic Fig. 95. — Sensory terminations in the adventitial arterial membrane of a cat. Ehrheh'.s method. (Cajal.) a — Sensory neurone, b aii'l d — Arterial wall, c — Seminal arborization. system. (2) Special visceral receptors, which are jirovided with highly devel- oped end-organs and are innervatetl directly from the brain and are not connected with the sympathetic system. General Visceral End-Organs. Of the general visceral group of receptors not much is definitelj^ known, although it is presumed that end-organs are provided for hunger, thirst, respiratory sensations and visceral pain. As a rule, the nerve endings of the general visceral receptors are either simple terminals in the visceral muscles or free arborizations in or beneath the mucous surfaces, without the development of special accessory cells to form differentiated end-organs. Special Visceral End-Organs. End-organs for the sense of taste com- pose this group. They are excited by chemical stinuilation and consist of taste-buds on the tongue and pharynx. These organs are responsive to sweet, sour, salty and bitter substances. The end-organ is a flask-hke collection of speciahzed epithelial cells supporting the specific sensory ending. The taste-buds are usually situated on the tongue in certain papillae which sur- round the end-organs. At the apex of the papilla is the taste pore through which the fluid reaches the sensory cells. EFFECTORS The effectors, by means of which nerve iminilses are distributed to the muscles and glands, are of two varieties: (f) somatic electors, and (2) visceral effectors. The Somatic Effectors constitute the end-organs in the striated skeletal muscles. These organs are made up of an end-plate which is a complex terminal arborization of the motor filler, associated with an elevated, granular mass of cytoplasm and a collection of nuclei in the muscle fiber. The Visceral Effectors constitute the end-organs of involuntary muscles. 90 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM WVll which may lie uiistripcd or stiipcd, as in the case of the heart. They are branched, free terminals ending on the surface of the muscle fiber. In the case of the heart iimscle, the nerve fibers usually have ex])anded tips. The end-organs of the glantls are fine unmyelinated fibers 'derived from the sympathetic system. These envel(jp smaller glands antl make their way through the largei' (jnes. FUNCTION.\L SIGNIFICANCE OF THE SOMATIC RECEPTORS Simple Tactile Sensibility (Thigmesthesia). This type of sensibility is tactile sense in its simjilest form. The receiptors for it are situated either about the liairs or constitute the tactile discs of Alerkel. Critical Tactile Sensibility (Topesthesiaj. This type of sensibility is particularly characteristic of the hairless jiarts of the skin, the palms of the hands, the M soles of the feet, and the lips, which are sensitized to a high degree of tactile discrimination, as indicated by their ability to localize areas in these parts and dis- tinguish the distances between two points (Weber's compass test). The receptors for this type of sensibility are the corpuscles of Meissner and the corpuscles of Grandry-Merkel. Pressure Sensibility of all Grades (Piezesthesia). The receptors for this type of sensibilit}' are specialized end-organs having a wide distribution in the body, the corpuscles of Pacini and their modifications. Muscle-Joint Sense (Myes- thesia, Arthresthesia). The re- ceptors f(jr tills type of sensibility are the muscle spindles of Ktihne, the musculo-tendinous e n d - organs of Golgi, the corpuscles of Golgi-AIazzoni and the entlings of Ruffini. Pain Sensibility (Algesthesia). The receptors for this type of sensi})ility are probably the free endings which are either intra- epithelial, intramuscular or intrafascicular. Temperature Sensibility (Thermesthesia). In this type of sensibility, two grades are rec- FiG. 90." Spindle of the pectoro - cutaneous mu.scle of a frog. In the inferior part, at B, is seen tlie ordinary motor ter- mination; the supe- rior part, on the contrary, shows the sensory termination. On account of the great distance sepa- rating these two terminations, a part of the striated m\i.s- cular fiber has 1-ieen left out. (C'ajal.) a — Myelin fiber, h — Vari- cose trunk of the epecui] arborization, B — Nerve fiber givini; origin to the ordinary motor termination, c — Sen- aory neurone. ,/ — Terminal varicose endings. THE IXTEGKATIOX OF THE XEUROXES 91 ognized: the critical and the affective perception of heat and cold. The receptors of affective heat sensibility are in all probability the free intra- epithelial endings on the surface of the body, while critical heat sensibility, according to some authorities, is mediated through the corpuscles of Krause. Equilibratory Sensibility. The receptors for this type of sensibility are the end-organs in the semicircular canals anrl the utricle and saccule. The Special Senses of SmeU, Sight and Hearing have their specialized receptors in the olfactory, visual and auditory organs. p.trts which amplify the relations betweex eeceptors and effectors; the mediators The agent by which the receptors and effectors are maintained in their proper relation is the central nervous system. This relation is accomplished through neural connections which establish continuity in the flow of afferent impulses from the receptors and efferent impulses to the effectors. The cells in the nervous system which make this relation possible are the mediators. The connection may be simple, bringing but few cells into action, as in the intrasegmental reflex, or may re- quire the cooperation of a large number of cells and several segments, as in the intersegmental reflex. For the most efficient action, the connection may demand the operation of the more complex portions of the brain and is then suprasegmental. Nuclei, Tracts and Pathways. The association of the several parts of the central nervous system for the perfor- mance of the more complex neural reactions depends upon the functional combination of several superposed neurone groups to form a pathway. Each neurone group in the central axis con- sists of a collection of tract cells which constitutes a 7iucleus whose axones become collected to form a tract. Thus one important cerebellospinal pathway is composed of three successive neurone groups brought into rela- tion with each other by means of synapses and consisting of (1) the cortico- dentate group, (2) the dentato-rubral group, and (3) the rubro-spinal group. In maintaining and providing the most efficient relations of the receptors to the effectors, these tracts and pathways form connections between the several parts of the central nervous system. As a result of these connections the receptors may produce an immediate response m the effectors called a simple reflex action or, by bringing the more highly developed parts of the brain into plav, they mav occasion an extensive correlation of nerve impulses which determines a complex, mediate response known as a neural reaction. Fig. 97. — Cerebello-rubro-spino- effector pathway. 92 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM The parts of the nervous system which the tracts and pathways serve to integrate, in this manner and for these purposes are: (1) the spinal cord segments; (2) the medulla oblongata; (3) the pons and cerebellum; (4) the midbrain; (5) the interbrain, and (G) the cerebral hemispheres. Till' spinal cord is also known as the myelon. The medulla oblongata, pons and cerebellum constitute the rhombencephalon , the midbrain is often referred to as the isthmii-^ I'licriihuli. The interljrain and cerebral hemis- pheres comprise the cerebrum. SPECIAL CLAS.SIFK'ATKIN OF THE REC'EPTOKS OF THE SKIN According to Botezat the receptors of the skin may be classified as follows: A. End-Organs of the Epiuehmis Simple Free Endings (a) S]iecific Intra-epithclial Branching 1. Branching with end-knots 2. Thin branching with end-knots 3. Broad end-branches 4. Thick fibers with lateral nets (Tretjakotfj 5. Loose pericellular filjer nets 6. Simple indifferent branching (6) Accessory Intra-epitholial Branching Cellular Endings — Merkel 's Corpuscles B. End-Orc;ans of the Dermis Simple Free Endings (a) Fiber Nets (loops) 1. Papillarv fiber nets and loops 2. Papillary fiber bundles (Ruffini) 3. Subepithelial fiber nets 4. Loose fiber nets (6) Branches L End-l)ranches on Ijasal membrane 2. Simple widely branched end-trees 3. Complicated branched end-trees 4. End-branches in l)one and cartilage (c) Knots L Simple 2. Combined 3. Ruffini's Corpuscles 4. Cenital Corpuscles (d) Intercalar}' Corpuscles 1. Simple 2. Compound Capsular Endings (a) Krause's End-bulbs L Simple 2. Compound ) THE INTEGRATION OF THE NEURONES 93 (b) Pacini's Corpuscles 1. Simple 2. Compound (c) Golgi-Mazzoni's Corpuscles 1. Simple 2. Compound (d) Capsular knots 1. Simple 2. With flat endings 3. Genital corpuscles Cellular Free Endings (a) Merkel's Corpuscles 1. Simple 2. Compound 3. Grouped Encapsulated Cellular Endings (a) Dogiel's Corpuscles (6) Meissner's Corpuscles , r,- , f Monolobar 1. Smrple | Multilobar 2. Modified f ?"^Pi^ , [ Combined C. End-OrcxAns in the Hairy Part of the Skin Sparsely-Covered Skin Epidermis 1. Simple 2. Cellular (Merkel's Corpuscles) Thickly Covered Skin Epidermis End-branching with end-knots (reduced) CHAPTER VI EXPOSURE AND INVESTIGATION OF THE SPIN.AL CORD IN SITU Significance of Spinal Relations. The highest degree of integration in the nervous system is attained in tire spinal cord and brain of man. Here the chief object of the integrative process is to assemble the nerve impulses flowing from the receptors in the most efficient combinations of nerve energy to influence the effectors of the body. Since the myelon or spinal cord is the more simple of the two major divisions of the central nervous sj'stem, it offers a convenient point of departure in the study of these central organs. For the student of the nervous system, and especiall}^ for the surgeon, a complete exposure of the central nervous system is of value because it affords an accurate realization of the relations between the cord and its envelopes, membranous, fluid and bon}^ Also of importance to the diagnostician and operating surgeon are the relations between the levels of origin of the nerves in the cord and the points at which the nerves leave the vertebral canal to enter their peripheral course. Incision Through Skin and Subcutaneous Tissues. The prelinunary in- cision should be made through the skin and subcutaneous tissue from the external occipital protuberance to the tip of the coccyx. A second incision curved in direction with its convexity upward should connect the tips of the two mastoid processes, its curve passing through the external occipital protuberance with the two lateral limbs of the incision corresponding to the superior curved line of the occipital bone. Depth of Incision in the Several Regions. In the cervical region the incision should then be deepened through the ligamentum nuchce down to the spines of the cervical vertebra; in order to separate the heavy masses of muscle on either side of the neck. In the thoracic region, the muscle mass being so much thinner, the prelimi- nary incision will be found to have passed down to the spines. In the lumbar region, the incision has to be deepened, for in this as in the cervical region, there are thick layers of muscle overljdng the vertebra. In the sacral region the vertebral column again closely approaches the surface, and the superficial incision will be found to be in contact with the underlying sacrum. Separation of Muscle Masses. Beginning from below and passing cranially, the muscle mass should Ije separated from the spines and laminae of the vertebrfe by the use of a periosteal elevator. The muscle attachments should be scraped clean from the spines and lamiiite in order to facilitate the opening of the vertebral canal. 94 EXPOSURE AND IN^'ESTIGATION OF THE SPINAL CORD IN SITU 95 Muscles and Fasciae Exposed. Although the arrangement of the mus- cles in the thoracic and sacral regions is not regular enough to allow a separa- tion into definite superficial and deep groups, nevertheless, in the cervical and lumbar regions, such a working differentiation can be made by means of the separation effected by more strongly developed fascial layers. In the cervical region the deep fascia is attached to the inferior curved lines of the occipital hone and is carried down into the neck as a partition between groups of muscles which can be called superficial and deep. In the lumbar region a similar layer may be made out stretching between the ribs above and the crest of the ilium below. This separates what may be called the axial from the paraxial muscles. Arteries Encountered in the Exposure. In the thoracic region the arteries encountered are the small dorsal branches from the intercostal arteries which pass backward through the costo-transverse spaces together with the posterior primary branches of the spinal nerves which supply the muscles of the back. Anastomosis between these vessels in the muscle fascia layers may produce a vessel of small size situated on either side of the spinous processes and also along the line of the tips of the transverse processes. A similar arrangement may be made out in the lumbar region where the branches come from the lumbar arteries, and also in the cervical region where they come from the occipital artery as its muscular branches, the arteria princess cervicis and the deep cervical artery. The occipital artery will be found curving around from the anterior cervical region between the superficial and deep groups of muscle to pierce the fascia between the insertions of the trapezius and the sterno-cleido-mastoid muscles. Periosteum and Bone Exposed. The muscles, having been separated from the spines and lamina, the periosteum of the occipital bone is stripped up from below, carrying with it the attachment of the muscles inserted into the occiput. This stripping is much more expeditiously per- formed if the periosteal elevator is pushed from below upward, on account of the fact that all the muscles which are inserted into the occiput pass up from below and their fibers, following the course of the muscle, tend to keep the elevator against the bone. As the muscles are separated from their attachments externally, search should be made for the mastoid emissary vein which emerges from the interior of the cranium and anastomoses with the superficial veins of the scalp. It is of variable size; at times it is altogether absent, but often may be 3-4 mm. in diameter. It is located usually along the masto-occipital suture, just above the level of the tip of the mastoid process. Nerves Encountered in the Exposure. The nerves which supply the muscles of the back and the urn-shaped area of skin bounded by the pari- eto-acromio-trochantero-coccygeal fines, of which more detailed mention will be made in the discussion of the dermatomic areas, are the posterior primary divisions of the spinal nerves. These nerves leave the mixed spinal nerves as they emerge from the intervertebral foramma and pass backward to be distributed to the muscles and skin of the back. 96 FORM AND FUNCTIONS OF THF CENTRAL NERVOUS SYSTEM Lower Limit of Dunil Sa Cerebellar Dura 3d Corvifal \'ertebra 4tb Cervical Vertebra 5th Cervical "S'ertcbra 0th Cervical \'ertcbra 7tli Cervical ^>rtebra 1st Thoracie "\crtebra 2d Thoracic Vertebra 3d Thoracic ^"ertebra 4th Thoracic Vertebra 5tii Thoracic "\>rtebra Oth Thoracic Vertebra 7th Thoracic Vertebra Sth Thoracic Vertebra flth Thoracic Vertebra 10th Thoracic \\.rtebra 1 1th Thoracic Vertebra 112(li Tliorn.'ic Vertebra 1st Lumbar Wrtebrn 2d Lunibar \'crtcbra .id 1 uinl.;ir \ertrbra ttli I.uml.ar ^■ertebra r.th Lunil,:ir \'ertebra icral \ertebra d Sacrid Vertebra cr;il \".Tlebra 1th Sacral \ertebra rjth Sacral ^■crtebra Coccj-x Kxternal Coccygeal Ligament FlQ. 9S. — Exposure of the tliirul sac. EXPOSURE AND INVESTIGATION OF THE SPINAL CORD IN SITU 97 In the cervical region, the first three posterior primary divisions have received special names: 1. The first, arising from the first spinal nerve, almost purelj- muscular, is called the suboccipital nerve . It supphes the complexus and the rectus capitis and the obhqus capitis nuiscles. Since the posterior root of the first cervical nerve is almost regularly lacking, the suboccipital nerve can have no sensory distribution unless it obtains it from a communication with the posterior primary division of the second cervical nerve. 2. The posterior primary division of the second cervical nerve is the great occiyital nerve and is distributed to the muscles of the neck and the skin over the occiput and upper part of the neck. 3. The posterior primary division of the third cervical nerve, the smallest occipital nerve, supplies the muscles of the neck and a small area of skin below that supplied by the great occipital nerve. The remainder of the posterior primary divisions are not supplied with specific names, but unite irregularly to form the -posterior cervical, brachial and lumbosacral qjlexus. Removal of the Bone. The spines of the vertebrae should now l^e re- moved, and this maj^ be most advantageously begun at the fifth lumbar spine. The thick spine is bitten off by means of heavy rongeur forceps close to its base. Angular rongeur forceps can then be inserted, catching the lamina to the right of the base of the spinous process betw'een its jaws. The lamina is then bitten through and the process repeated on the left side of the base of the spinous process. Passing upward, the spines and laminse of the succeeding vertebrae are similarly treated until the entire posterior bony covering of the vertebral canal is removed. This is relatively easy in the lumbar and cervical regions, owing to the fact that there is no overlapping of the spines and laminae. It is somewhat more difficult in the thoracic region, owing to the obhque incfination backward and downward of the dorsal spines, but with a little care the removal may be accomph.shed without opening the dural sheath. The laminae should be completely removed in order to provide as much space as is obtainable. In the thoracic region some care will have to l)e exer- cised in order that the relatively shallow intervertebral foramina be not encroached upon and the emergent nerve roots damaged. Exposure of the Dura Mater. The posterior arches of the atlas are similarly divided and the posterior margin of the foramen magnum is exposed . Attention should be directed toward the removal of the laminaj and tubercles on the posterior or dorsal surface of the sacrum. When this is accomplished, the entire vertebral canal lies open, thus exposing the dural sac. Lying upon the dura, between it and the bony envelope, is found a variable amount of adipose tissue, in which ramify the arteries andvains suppljdng the membrane. Superiorly the dura is found to be firmly adherent to the foramen magnum ; below the foramen magnum the spinal dura is free 7 98 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM iid'}\0. Fig. 99. — Dissection showing lateral view of spinal cord and brain with dura mater exposed, ihiiiirgrrii.) from the vertebrse and connected to them only hy means of dehcate fibrous strands. At the foramen magnum the spinal dura is continuous with the cranial dura, A\hich is intimately adherent to the interior of the cranium especially over the base, at the suture lines and over bony prominences. At intervals along the sides of the dural sheath, the spinal nerves will be seen passing from their points of emergence through the dura to their foramina of exit between the vertebrae. The varying course of these emer- gent and entrant nerves will be studied in detail when the dura is opened. Emergence of the Spinal Nerve Roots. Lexoth of the Nerve Roots. The course of the mixed nerves from points of origin in the cord to points of emergence tlu'ough the inter- vertebral foramina is mainlj- intradural; but since they do not leave the dural sac exactly opposite the foramina which are to transmit them, they have an intraspinal course which is varial.ile in length. The distance between the point of emergence from the dura and the intervertebral foramina is not the same at all levels, being short in the cervical region and increasing in length from above downward. In the upper thoracic region, this distance is shorter than in the lower cervical region, but as the thoracic, lumbar and sacral regions are reached, the distance becomes greater. Relation's of Dura to Roots. At the point of passage through the dura in the cervical region, the nerve presents a gentle curve with its concavity upward; in the thoracic region this curve becomes rather a sharp angulation which, on passing down- ward, is gradually straightened out imtil in the lumfiar region the extradural course is a direct prolongation of the intradural course of the nerve. The dura, as each spinal nerve pierces it, sends out a tuljular prolongation surrounding the nerve, which becomes firmly adherent to the nerve just beyond the dorsal root ganglia of the posterior root as it lies in the intervertebral foramen. EXPOSURE AND INVESTIGATION OF THE SPINAL CORD IN SITU 99 I Cerebellar Dura Mater Cervical Rpsion of the Spinal Cord Reflected .Spinal Dura Mate I Cut Edge of Cerebellar Dura Mater ; Junction of Medulla and Spinal Cord ^C 1 Thoracic Rpgion of the Spinal J Cord Dentif-ulations of the Li^ rnentum Denticulatum Lumbar Recion of the Spinal < Cord Sacral Region of the vSpinal Cord Caudal Fork of the Ligamen- tum Denticulatum in Rela- ; tion with L 1 Reflected Spinal Dura Mater [ Termination of the Spinal Cord Cauda Termination of the Spinal Dura Mater Sacral Hoots - C'occyx . I" T 12 L 5 S 5 Co 1 Cocc>-geal Ligament Fig. 100. — E.xposure of the dorsal , surface of the spinal cord, showing the radicular fans nerve roots, ligamentum denticulatum and cauda equina. 100 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Arteries of the Vertebral Canal. The arteries of the vertet^ral eanal are derived from the \'ertefjral arteries in the cervical region, from the intercostal arteries in the thoracic region, and in the lumbar region from the four lumbar arteries which are derivatives of the parietal supply of the abdominal aorta. In the sacral region they arise from the middle sacral artery, a branch of the aorta. From these arteries small branches are given off which pass through the intervertebral foramina and divide into branches which supply the spinal cord and tlie vertebrae. These vertel^ral vessels divide into ascending and descending branches which by anastomosing with similar ve.ssels from above and below, produce a doulde anastomotic chain 13'ing along the posterior surface of the vertebral bodies close to the base of the pedicle on each side and connected with each other across the median line by anastomotic branches. The Veins of the Vertebral Canal. The veins of the vertebral canal form a rich plexiform arrangement bioth without and within the vertebral column. The A'cins on the outside are arranged in two plexus. 1. The aiifcr/or -plexus, which .surrounds the Ijodiesof the vertebras, forms an external line of venous drainage. 2. The posterior plexus surrounds the spines, laminse and transverse pro- cesses of theverteljra^and may cause troufdesome hemorrhage during opera- tive procedures. These two lines of drainage lielong to the dorso-spinal venous system. The venous channels within the vertebral canal are of greater interest and constitute the meningo-rachidian veins (plexus venosi vertebrales interni). They consist of two longitudinal plexus, the anterior along the posterior surfaces of the bodies of the verteljrie, the einterior longitudinal vein, and the posterior in contact with the laminie, the posterior longitudinal vein. These veins drain the bodies of the vertcfira?, tlie meninges and the epidural fat, form a rich anastomosis across the liodies of the vertebra and com- municate with the vertebral, the intercostal, the lumliar and the middle sacral veins which in turn drain into the superior and inferior vena cava. Caudal Limit of the Dural Sac. The dural sac extends caudally as far as the second sacral vertefira where it terminates bj- forming a blind sac. The lower three sacral nerves and the coccygeal nerve all perforate the lower end of this sac and pass to their foramina of exit. The lower end of the dural sac is attached to the lowermost part of the sacrum and the coccyx by small bands of fil irons tissue. Incision of Dura, Exposing Subdural Space, Arachnoid and Pia Mater. The posterior aspect of the dura may now lie opened throughout its entire length 1>\' a longitudinal incision, and an investigation of the membranes whicli surr(.)und the coi'd within the dura can be made. The Arachnoid. The next mcmljrane encountered is the arachnoid. This mendjrane is a delicate non-vascular tissue which corniiletely surrounds the cord and the brain. It is continuous al)Ove -with the cranial arachnoid at the foramen magnum. It is m cjuite close contact with the dura, the space between the dura and the arachnoid liemg relatn'elv small. EXPOSURE AND im^ESTIGATION OF THE SPINAL CORD IN SITU 101 The Subdural Space. The space between the dura mater and the arachnoid is called the subdural space, and is nowhere in communication with the space within the arachnoid. The arachnoid also forms sheaths over the spinal nerves, these sheaths fusing with the spinal nerves over the dorsal root ganglia. The arachnoid may now be torn from the posterior surface of the Cord and the pial covering examined. The Pia Mater. The pia mater is a delicate, highly vascular membrane which covers and is intimately associated with the cord and its nerves. It dips into the furrows and sulci and carries with it the blood vessels des- tined for the nourishment of the cord. The Subarachnoid Space and Spinal Fluid. In the hving subject, the subarachnoid space is ciuite extensive and is filled with tlie spinal fluid. Jn the cadaver the space will be found empty, the arachnoid collapsed and in con- tact with the pia mater. This collapse is caused by the rapid absorption by the central nervous system of the spinal fluid after death. Ligamentum Denticulatum. This structure, considered by some to be the suspensory ligament of the cord, arises at the level of the foramen mag- num and continues throughout the length of the cord to end opposite the first lumbar vertebra. At the level of the foramen magnum, the ligament arises as two leaves, one from the anterior half of the edge of the foramen magnum, the other from the posterior half; these approach each other and fuse to form the ligament. The mesial attachment of the ligament is to the entire length of the cord; laterally its attachment to the dura is not continuous but is effected by a series of denticulations which Ix'come incorporated in the dura. There are twenty-one of these processes which alternate with the corresponding spinal nerves, a denticulation being inserted into the dura between each two succes- sive nerves. Between these insertions the ligament presents a gentle curve whose concavity is directed laterad. Mesially the attached portion be- comes continuous with the pia and, through the fibrous prolongations of the latter membrane into the substance of the cord, gains an attachment to the cord itself. Caudal Fork of the Denticulate Ligament. Caudally the ligament ends opposite the first lumbar vertebra in a fork-shaped extremity, the lateral limb of the fork being adherent to the dura, the mesial hmb extending along the conus to its tip, where it fuses with its fellow of the opposite side and is continued down over the fi-lum terminale, a large part of which it forms. Over the fork of the denticulate ligament passes the dorsal root of the first lumbar nerve to meet its ventral root and thus become the mixed nerve. This relation is of considerable importance in the surgery of the cord and spinal nerves, for it supphes a reliable guide to the identity of one nerve root with which, as a starting point, it is relatively easy to determine the identity of the nerves above and below. Examination of the Cord and the Emergent Roots. The adult spinal cord extends from the margin of the foramen magnum to the level of the 102 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Superior CoUicull Inferior Colliculi Middle Cerebellar Pedunfle Superior Cerebellar Peduncle Inferior Cerebellar Peflunclc Medulla Cervical Region of .Spinal Cord j Cut Edge of Spinal Dura Mater Intercostal Musclcy Thoracic Region of Spinal , Cord Intercostal NL-rvi. Lumbar Region of Spinal < Cord Sacral Region of Spinal Cord Cauda Equli Cochlear Division of Eighth Cranial Nerve Ninth. Tenth and Eleventh Cranial Nerves Vertebral Artery C 1 Tran3\'erse Process of Atlas C 2 Transverse Process of Axis C ;i Third Cervical Transverse Process Fourth Cervir'al Transverse Process C 4 Fifth Cervical Transverse Process i—P Sixth Cervical Transverse Process ^■■'' Seventh Cervical Transverse Process 12t!i Itib T 12 1st. l.iiriibar Transverse Process bar Tr;m;svcrsi-"i Process d T,unibar Transverse Process •rse Process 5th Lumbar Transverse Process L5 Fig. 101. — Dorsal view of the cerebrospinal axis with the ori}:iitis of the peripheral nerves showing their relations to the vertel.^ral column. EXPOSURE A.ND INVESTIGATION OF THE SPINAL CORD IN SITU 103 lower border of the first lumbar vertebra or the upper border of the body of the second lumbar vertebra. In two regions there are enlargements mainly in favor of the transverse diameter. Location of Cervical Enlargement. The upper enlargement is in the cervical region and is located between the third cervical and second thoracic vertebrae, its maximum being o-piposite the fifth or sixth cervical vertebra. This enlargement is produced by the development within the graj^ matter of the cord of the large collections of cells which are destined to control the muscles of the upper extremity, and from it arise the 5th, 6th, 7th and 8th cervical nerves and the first two thoracic nerves. The enlargement is called the cervical enlargement or the intumescentia cerincalis. Location of the Lxjmbar Enlargement. The second enlargement begins about the level of the 10th thoracic vertebra, reaches its maximum development opposite the 12th thoracic vertebra and then tapers gradually away into the conus mediillaris and the tip called the eyiconus. From this enlargement take origin the nerves destined for the supply of the lower limb, including the 3rd, 4th and 5th lumbar and the 1st, 2nd and .3rd sacral nerves. The lumbar enlargement is also called the intumescentia lumhalis. Relations of the Spinal Cord and Nerves in situ. The numbering of the nerves in relation to the vertebral foramina through whicli they pass shows some variations. This is due to the fact that in the cervical region there are eight cervical nerves, whereas there are but seven cervical vertebra. The first cervical nerve emerges from the vertebral canal above the atlas be- tween it and the occiput, hence the cervical nerves are numbered in relation to the succeeding vertebra except the eighth, which emerges above the first thoracic vertebra. The thoracic nerves are numbered in relation to the preceding vertebra, the first thoracic nerve emerging below the first thoracic vertebra and the twelfth nerve below the twelfth thoracic vertebra. The lumbar, sacral and coccygeal nerves in like manner are numbered in relation to the vertebra below which they emerge. Relation of Root-Origin to Root-Foramen. The origin of the nerves from the cord segments to which they belong does not correspond to the vertebra opposite which they he. Consequent upon the increase in bulk of the lower cervical region, this discrepancy is in large part made up, liut m the thoracic, lumbar and sacral regions there is an increasing obliquity in the intraverteliral course of the nerves from the level of the second thoracic vertebra downward to the lowermost part of the canal, where the coccygeal nerve, after traversing an intravertebral distance of 28 cm. from its segment of origin, emerges from its foramen. Relation of Cord Segments to the Vertebral Column. The cer- vical nerve segments correspond roughly with their respective vertebra. The third thoracic segment, located above its corresponding vertebra, lies opposite the second thoracic vertebra. The sixth thoracic segment corresponds to the body of the fourth thoracic vertebra. The ninth thoracic segment corresponds to the seventh thoracic vertebra. 104 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM The twelfth thoracic segment corresponds to the bodj^ of the ninth thoracic vertebra. The jwe lumbar segments correspond to the bodies of the 10th. 11th and 12th thoracic vertel)r;e. The fire sacral secjmenis and eme coccygeal segment correspond to the intervertebral tlisk between the r2th thoracic and 1st lumbar vcrtcbrie and the body of tlie 1st luniljar vertebra. In the cerucal region, the dorsal root of the first cervical nerve may be found to be entirely lacking or represented by a very fine filament. This absence is explained by the I'act that the trigeminal nerve has taken over the area supplietl liy the first cervical nerve. Spixal AccE.ssOKYXEin'E. Emerging from the lateral aspect of the cord, between the attachment of the ligamentum denticulatum and the emergence of the dorsal ner^'c roots, beginning at the lei el of the 6th cervical segment, will be seen a series of nerve fasciculi which form the spinal portion of the spinal accessor!/ nerre. This line of emergence moves slightly backward as it is traced upward. The fasciculi join and form a nerve trunk wliich passes cranially ix'twcen the denticulations of the denticulate ligament and the posterior nerve roots to enter the skull, where it is joined by its accessory portion at the jugular foramen to liecome the spinal accessory nerve. Removal of the Cord. Before the cord is removed from the vertebral canal, its relations to the medulla should lie examined. On the posterior surface, it kIW be observed that the grooves found on the cord are continued on the surface of the medulla. The dorsal sulcus remains as before, except that as it is traced upward it becomes somewhat more pronounced. The dorso-lateral sulcus also remains, but begins to show a tendency ot diverge toward the lateral surface. The areas between the dorso-median sulcus and the dorso-lateral sulcus and that external to the dorso-lateral sulcus begin to show a greater prominence. The cord should now be cut through opposite the margin of the foramen magnum and each pair of spinal nerves should be divided as close to the dural foramina as possible. The denticulations of the denticulate ligament should be divided and the cord lifted out of its bed in the dura. CHAPTER VII THE SPINAL CORD ITS GENERAL CHARACTER AND ANATO:\IY Form of the Spinal Cord. The spinal cord is a long cylindrical structure occupying the greater portion of the vertebral canal and extending from the border of the foramen magnum in the skull to the lower Ijorder of the first lumbar vertebra. Although generally cylindrical in form, it presents con- siderable ventro-dorsal flattening, and in certain areas its diameters are greater than in the regions immediatelj' above and below. These areas are spoken of as the spinal cord enlargements, of which there are two, one in the cervical region, the cervical enlargement {intumcsceniia cervicalis), and one in the lumbar region, the lumbar enlargement (intumescentia lumhalis). At its caudal extremity, the spinal cord tapers and ends in a slender filament, the filum terminale, or central ligaynent of the spinal cord. Regional Differences in the Spinal Cord. AVhen stripped of its surround- ing pia mater the cord appears glistening and white. Its consistency is firm, although it readily yields to pressure and becomes distorted. This fact is of practical importance, since it indicates the necessity for delicacy in surgical manipulation. It is possible to distinguish certain regions in the spinal cord because of the presence of the two enlargements already mentioned. These regions, enumerated from the upper portion of the spinal canal toward the coccyx, are (1) the cervical region; (2) the thoracic region; (3) the lumbo- sacral region; (4) the conus terminalis, and (.5) the filum terminale. Significance of the Several Regions of the Spinal Cord. The cervical enlargement develops in consequence of the increased demand for innerva- tion by the upper extremities; and in like manner the lumbar enlargement appears in response to the demand for greater nerve supply to the lower extremities. This fact is demonstrated by embryology and also by compara- tive anatomy. It has been shown that in the early stages of development, before the limbs make their appearance, the spinal cord is completely cyhndrical from its cephalic to its caudal extremity. As soon as the limbs are developed, however, the two enlargements make their appearance and thus provide the greater number of nerve cells for the regulation of the movements of the extremities. Comparative anatomy confirms these observations, since it has been .shown that in the animal series the two enlargements of the spinal cord bear a constant relation in their dimensions to the size and purposes of the extremities. Both enlargements are well marked in the bipeds in which, as in man and the anthropoid apes, they reach considerable dimensions. On the other hand, the enlargements may be much reduced in size in animals which have rudimentary extremities. The lumbar enlargement, for example, 10.5 106 FORM AND FUNCTIONS OF TITK CENTRAL NERVOUS SYSTEM Roots of Arci'ssory Nfrvi-. 8piij;il Dura MhUt 1st Cervical Nerve 1st Thoracic Nervf ' Pons \'arolii \ Cervical Spinal Cord Lateral Column . \ Thoracic Spinal Cord Ist Lumbar Ner^-e lat Sacral Ne ^ Ijurnbar Spinal Cord Fig. 102.— Spiinil coi-..l vi<.-\\i.m.I Iruui Ike nght. {Spaltcholtz.) THE SPINAL CORD 107 IS small in the aquatic mammals, such as the seal and the cetacea, the cervical enlargement, similarly, is small in the marsupials, such as the kangaroo, while both enlargements are absent in animals which have no extremities, such as the serpents. The portion of the cord intervening between the cervical and lumbar enlargements is relatively small in its diameters, because the musculature which it controls is not only less extensive but less capable of complex activities. The tapered portion forming the conus terminahs is repre- sentative of a region in the body much less extensive in its executive organs and receptors than other parts. Dimensions and Weight. The spinal cord in the adult male varies from 43 to 45 centimeters in length or about 17 to 18 inches. It is somewhat shorter in the female. I cervical enlargement is 38 mm. Its circumference in the { lumbar enlargement 33 mm. [ intermediate portion 27 mm. I cervical enlargement is 13 mm. Its transverse diameter in the •! lumbar enlargement 12 mm. [ intermediate portion 10 mm. I cervical enlargement is 9 mm. The antero-posterior diameter of the ■ lumbar enlargement 9 mm. [ intermediate portion 8 mm. The length of the filum terminate is from 17 to 18 cm. Freed of its membranes and detached from its nerve roots, the spinal cord weighs from 26 to 30 grams in males and 1 or 2 grams less in females. At birth the weight of the spinal cord in proportion to that of the brain is 1 to 100, while in the adult the ratio of spinal cord to brain is 1 to 50. The main increase occurs in the first two years of life. The weight of the spinal cord in the new-lsorn is 3 to 4 grams and the average length is 14 centimeters. At birth the length of the body bears the proportion to the spinal cord of 10 to 3; at the end of the first year this ratio has changed to 12 to 3, while in adult life in the average male of six feet in height, this same proportion is maintained. The relative weights of the different portions of the central nervous system are as follows: Spinal cord 30 grams Medulla oblongata, pons and midbrain 26 gram.s Cerebellum 140 grams Cerebral hemispheres H-'O grams Entire brain 1366 grams On the basis of these figures it is apparent that the combined weight of the medulla oblongata, pons and midbrain is about equivalent to that of the spinal cord. The eereljcllum is five times as heavy as the spinal cord and the cerebral hemispheres about forty times as heavy. [ gray matter of the spinal cord is 1 . 0382 white matter of the spinal cord is 1 . 244 The age of the individual. In the new-born the sjiinal cord ex- tends to the third lumbar or even to the fourth lumbar vertebra. In the THE SPINAL CORD 117 sixth month of intra-uterine Hfe the tip of the conus terminahs corresponds to the base of the sacrum, while in the third fetal month the cord occupies Fig. 111. — The extent of the spinal cord of the fetus at the fifth month. (Compare with Fig. 112). (Elsberg.) the entire length of the vertebral canal and descends as far as the base of the coccyx. During the several stages of development the spinal cord seems to ascend in the vertebral canal in such a wa}' that the tip of the conus termi- nalis loses its original relation with the coccyx. It gradually assumes a position higher in the canal and finally attains its adult relation with the lower border of the first lumbar vertebra. This movement of ascension on the part of the cord is apparent and not real. It is due to a disparity in growth between the vertebral column and the cord. The result of this dis parity is a seeming upward shift of the conus terminalis. During this change in relations, the nerve roots of the lumljar, sacral and coccygeal segments become greatly elongated in order that they may retain their original con- nection with the cord and at the same time make their emergence from their proper intervertebral foramina. Two important features develop in conse- quence of the disparity in growth between cord and column: (1) The caudal portion of the vertebral canal which in fetal life contains the spinal cord no longer does so in the adult. (2) This caudal portion of the canal in the lis FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM adult contains the elongated root fibers connected with the lumbar, sacral and coccygeal segments of the spinal cord, which make their emergence through the intervertebral foramina of the lumbar, sacral and coccygeal portions of the column. Their collected fibers constitute the Cauda equina. l''iG. 112.— The extent ul' tlie spiii:il cnnl in the ;ehill, eiile encasement, so that many movements of the body involving flexion, rotation and gliding of the vertebral bodies may be produced without injury to the cord. Although the bony capsule surrounding the spinal cord affords adequate protection against usual strain, the nature of the canal and its bony character make the spinal cord peculiarljr liable to serious damage from unusual strain. The cord under certain conditions, being held in a fixed position, has no chance of escape and must bear the full I) runt of injurj^ due to disloca- tion or fracture of its bony envelope. While the vertebral column, therefore, affords excellent protection against ordinary stress, it becomes an actual disadvantage to the spinal cord in the event of severer injury. Within the Ijony capsule there is a series of envelopes of equal importance. The outermost of these is the dura mater, or pachymeninx. The second membranous envelope is the arachnoid. The third envelope is unlike the others; it consists of a transparent hquid, the cerebrospinal fluid, which surrounds the spinal cord like a water jacket. The fourth and innermost capsule is a delicate, vascular membrane, the pia mater, also known as the Icptomenui.r. Spinal Dura Mater. In its general outlines, the dura mater presents itself as a cylindrical tul)e lying within the verteliral canal and extending from a firm attachment to the border of the foramen magnum as far caudally as the second or third sacral vcrteln-a. The dura mater does not come in direct contact with the inner surface of the bony canal, and there is a consideraljle space Ijcttt'een it and the outer surface of the spinal cord. The space between the dura mater and the bony 119 120 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM wall of the vertebral canal, called the supradural space contains a semifluid, fatty substance. The external surface of the dura mater is traversed by many large venous channels. Dorsally it is almost entirely free of any connection with the inner surface of the vertebral canal. Ventrally, however, it is attached to the com- mon posterior vertebral ligament by a system of fibrous prolongations which r^ e Z^ O 7!! hO M G 1=1 a "t-i _o > ^ O p m c I ai'e most pronounced in tlie cervical and lumbo-sacral regions, and most feebly develojied in (he (li()raci(t regiim. L'r(.ini iis lateral aspects the dura mater gi\'es <.ilf a series of neui-al i)rol(jngations or sheaths, \\hich cn\-elop the spinal nerves and accompany the latter as far as their point of exit from the intervert(>l)ral foramen. Each spinal root at its point of entrance into the intervertebral foramen receives a special, separate investment from, the dura. The ventral and dorsal root sti'ands as they approach their conlluence THE SPINAL CORD 121 are encased in a separate dural sheath as far out as the external extremity of the spinal root ganglion. When the actual junction between the dorsal and ventral root strands occurs, the two separate sheaths of dura merge, and the mixed nerve is then surrounded by a common dural sheath. The root strands, the dorsal root ganglia and the mixed nerve are firmly fixed m the intervertebral foramen by connective tissue processes attached to the bone and to the dura. The internal surface of the dura mater is opposed to the external sur- face of the arachnoid, with which it is in intimate connection. The arachnoid is adherent to the inner surface of the dura mater by means of a number of connective tissue prolongations. Along the longitudinal line determined by the points at which the nerve roots come into relation with the dura mater the denticulate ligament is attached by means of a series of serrated pro- cesses. The attachments of the ligament extend from the cephahc extremity of the spinal canal to the root of the first lumbar nerve. In relation with the attachment line of the denticulate ligament are several small apertures arranged in pairs, marking the point of entrance of the nerve roots into their dural sheaths. Each pair of openings is so arranged that the ventral aper- ture has a slightly higher plane than the dorsal. These apertures are vari- able in their disposition and may be separated by one or two milhmeters. In some cases, the root strands dip into their neural sheaths through a single aperture in the dura. As a rule, the blood vessels which go to the spinal cord pass through the same orifices with the roots. Exceptionally, however, the blood vessels have independent passagewa3^s of their own. The Upper and Lower Extremities of the Dural Sac. The upper extrem- ity of the dural sac is firmly attached to the margin of the foramen magnum. The lower extremity lies in the sacral canal and contains the fibers which con- stitute the Cauda equina. Caudally, the dural sac terminates in a cone-shaped prolongation at the lower border of the second sacral segment. Its termina- tion is called the dural cul-de-sac. Although the dural sac extends to the lower boundar}' of the second sacral segment, the dura itself is prolonged downward through the remainder of the sacral canal as separate processes, ensheathing the lower fibers of the Cauda equma and forming a covering for the filum terminale. The process of the dura in relation with the fiknn reaches caudallj- as far as the dorsal portion of the first coccygeal segment, where it is firmly attached to the bone. This portion of the dura is the coccygeal ligament of the spinal cord. In its entire length, the dural cul-de-sac is attached along its ventral surface by means of fibrous prolongations to the dorsal common vertebral Hgament. These prolongations are irregularly fenestrated, and constitute the ventral ligament of the dura mater of Trolard. Separate prolongations from the cul-de- sac form neural sheaths about the second, third, fourth and fifth sacral nerves and also about the first coccygeal nerve. These sheaths extend from the external surface of the cul-de-sac to the several foramina of emergence of the sacral and coccygeal nerves. The dorsal root ganghaof the first, second and third sacral nerves lie in their dural sheaths immediately external to 122 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM the dural cul-dc-sac, while the gangha of the fourth and fifth sacral nerves and the first coec^'geal nerve lie within the sacral canal at a considerable distance from the cul-de-sac. Spinal Arachnoid. A second membranous envelope surrounding the spinal cord lies immediately within the dui'a mater. This is the arachnoid. Its outer surface is intimately adherent to the inner surface of the dura, a eonnectioir established bj^ fine, filamentous, connective tissue processes. The arachnoid is a membrane without blood vessels, consisting of two 1am- inie which are separated by a narrow cleft, tiie arachnoid space. The outer or parietal layer of the arachnoid is attached to the inner surface of the dura. The inner or visceral layer is a thin and transparent membrane extending the entire length of the cord and for some distance upon the cauda equina. It descends asfar as the ajjex of the dural cul-de-sac, where it is reflected out- ward to become continuous with the parietal layer. The arachnoid is sepa- rated by a spacious cavity from the spinal cord. This is the subarachnoid space. Between the visceral and parietal la}-ers of the arachnoid, there is a small interval called the arachnoid cavity. This space is traversed by many connective tissue trabecule which hold the parietal and visceral layers to- gether. The ca\'ity is filled with a serous fluid. The following structures pass through the arachnoid and in their passage receive a serous sheath from it. 1. The dural exti'cmity of the denticulate ligament. 2. The ventral and dorsal root filiei's of the spmal nerves. 3. The bloixl vessrls which accompanj- the roots. Spinal Pia Mater. The innermost envelope surrounding the cord is intimately attached to that (jrgan and sends many thui septal ])rocesses, the septula, into the substance of the white matter. It consists of an internal and external layer between which run the man}- lilood vessels supplying the substance of the spirial cord. The internal layer is intimately attached to the cord, Ijoth liy means of the septula and also l)y numerous vessels which enter the medullary substance. In the ventro-median fissure, the pia mater dips into this sulcus, co^'el■irlg i;'acli side of it. At tlic doi'so-median sulcus, tlie inner layer sends in a long process wliich cdustitutes the dor.so-rnediari sr/itiun. Tlie external la>'er of the ])ia mater is liatlied l)y the cerel)ros]3inal fluid which separates tile pia fi(im llie ;irai'hiioid. This surface of the pia mater is attached to the dui'a l)y means of tlic deiilirulate ligaments which extend from the lateral asiiect "f the sjiinal cord as a thin and delicate liand of pia mater i-ontaiiiiiin no l)loiiil vi.'ssels. The line of attachment is midway lietween the ventral and dorsal root fibers. By its inner border this ligament is at- tached wilhiiul iiitei'ru]_if idii 1(1 the s])inal cord from its ceiihalic to its caudal extremity :iiid terminates at tlie liegiiining of tlu' conus terminalis. Along its outer boi-der, allhough it jn-esents a firm atlnclunent t(j the dura, the line of junction is not complete but is characterized l)y a series of denticulate ])roc- esses between which are a sei'ies of ari.-ades to iierniit the ]iassage of root fillers. The first denticulate insertion is situated at the level of the lateral mass of tlie atlas; the last inserti(m occurs Ijctween the twelfth thoracic THE SPINAL CORD 123 and the first lumbar nerve. Each denticulate ligament has twenty-one pomts of lateral attachment, although in certain exceptional cases", this number may l)e reduced to sixteen or eighteen. The cephalic extremity of the spinal pia mater is continuoiis with that covering the medulla oblongata. Caudally, it passes over the conus termmalis to cover the filum terminale which it envelops throughout its entire length. Structure of the Membranous Envelopes of the Spinal Cord. The dura mater covering the spinal cord is continued into the skull, but in this relation presents a marked change from that observed in the vertel)ral canal. Immediately upon passing into the skull above the foramen mag- num, the dura presents two distinct layers; (1) the parietal layer, firmly attached to the inner surface of the cranial bones, and (2), the visceral layer, in contact with the arachnoid. The spinal dura mater presents but a single layer, namely, the visceral or internal lamina which consists of a white fibrous tissue whose strands are longitudinal in direction and inter- lace with a small number of yellow elastic fibers. The dura contains arteries, veins and lymphatic vessels. It is innervated by meningeal branches from the dorsal roots of the spinal nerves. The outer surface of the arachnoid is covered by endothelial cells, sup- ported by a delicate framework of connective tissue fibers. The inner surface is reinforced l)y a certain number of yellow elastic fibers. The arachnoid contains no blood vessels, but nerve fibers from the trigeminus, as well as from the spinal nerves, have been described as forming a rich plexus ramifying throughout the membrane. The pia matter is composed of two laminte of connective tissue. The external lamina consists of fasciculi disposed longitudinally and parallel to the long axis of the spinal cord. According to some authorities, l)oth sur- faces of this lamina are covered bj' endothelial cells; this may be ciuestionable concerning its inner surface, but the outer surface is undoubtedly endothelial in nature. The internal lamina, or intima-pia, so called by Key and Retzius, is formed f)>' connective tissue fibers having a circular arrangement, in the meshes of which is a system of lacuna filled with lymph. Prolongations from this lamina make their way inward accompanving the blood vessels, in all proljal)ility forming the perivascular lymph spaces. This lamina of the pia mater probably contains the h-mphatic channels of the spinal cord. In the strict sense there are no lympluitic structures found in tlie cord. Between the two lamince which constitute the spinal |Ma mater, there is a small lymphatic space, the intrapial hjiiipli space. This communicates with the suljaracluioid space on the one hand and with the lacuiue of the intinta- pia on the otlier, where these enter into the formation of the perivascular lymph spaces. The blood vessels of the jiia are situated lietween the two layers whicli form this membrane, the internal lamina accompanying the vessels as they penetrate into the substance' of the fortl. This relation is of considerable clinical importance, as it explains the )jossi))ility of the subpial and intrapial hemorrhages. Lymphatics in the strict sense are not found in the pia mater. On the other hand, the rather spaciOLis intrapial space 124 FOKM AND INUNCTIONS OF THE CENTRAL NERVOUS SYSTEM may, in the li.nlit of its connection with the perivascular lymph spaces, be regarded as a lar^e lymph reservoir. A rich plexus of nerve fiVjers derived from the sympathetic sj'stem ramifies through the pia. These fibers are probably vasomotor in nature and serve to rcj^idate the circulation in the spinal cord. The Cerebrospinal Fluid. Filling the space between the pia and the arachnoid, is an important envelope completely sarrounding the spinal cord. This is the cerebrospimil fluid. It is important not only because it serves as a buffer for the purpose of absorbing shocks which would otherwise fall too directly upon the spinal cord, and because it plays some nutritive role in the metabolism in the nerve tissue, but also for the reason that under many pathological conditions it is subject to marked departures from its normal characteristics. The total amount of the cerebrospinal fluid contained within the ventri- cles of the brain and in the subarachnoid space varies from 100 to 150 cubic centimeters. It is a colorless, transparent and odorless fluid. When held up to the light, it has the appearance of water and is free of flocculency under normal conditions. Its reaction is mildly alkaline: its specific gravity is 1.007. Within the subarachnoid space it exists under a definite tension which is slightlj^ greater than atmospheric pressure. This pressure has been measured by means of lumbar puncture and is estimated to vary normally between 100 and 150 millimeters of water. When allowed to flow during lumbar punc- ture, it escapes drop by drop at aljout 60 drops per minute. The Constituents of the Spinal Fluid are : Water 98.700 Cholesterin 0.210 Sodium and Potassium chloritle O.SOl Sodium carbonate of Calrimn phosphate 0.017 Sodium sulphate 0.20 Globulin 0.088 The spinal lliiid also contains glucose in amounts varj'ing from 40 to 60 grams per liter and urea 0.25 to 0.35 grams per liter. It contains faint traces of peptone. There is no fibrinogen in the fluid, and if left to itself it does not coagulate under normal conditions. In ad in the sub- . 115. — A diagrammatic representation of tlie vertical extent and relative transverse proportions of the lateral and central motor cell columns of the ventral gray matter of the spinal cord. The relative position of the lateral splanchnic cell column in transverse section is indicated at the riglit. 5 I 5i CEMTRAL noTOR CEiXCOLUnn S J LATERAL iPLAMCHhlC .■''nOTCR CELL coLunn THE SPINAL CORD 131 N Fig. 116. — The cell groups in the gray matter of th.Q cervical region of the spinal cord. The letters on the diagrams represent the 'following cell-groups: A — The cells of the substantia gelatinoaa of Rolando. B — The cervical and sacral nuclei of stilling — the mesial basal group of the dorsal horn. C — Clarke's column. D — The ventro-mesial cell column. E — The dorso-mesial cell column. (r— The ventro-lateral cell column. H — The intermediate dorso-lateral cell column. 7 — The central cell -The ventro-later... ■._,. .,...,.... column. A' — The dorso-lateral cell column lateral cell column — splanchnic A' — The s L — -The lateral basal group of the dorsal column. M — The linal nucleus of the spinal accessory nerve. 132 k(ii;m Axii functkixs oi.- the cextkai. .neiu'dts system staiitia iiclal iiKisa of U.olaiiiln. I'kjIIi of (lolsiV types of nerve-eells are ol)- sci-ved, the ( loli^i tyi)e I lieiii'j, pvesent, iii all portions, while the GoIkI type II is rcstrietcd to (lie (hn'sal ^I'^iy eoluiiin. The Golgi typo II cells send tlieir axoiies foiwai-d IVoni tlu' dorsal ,nra>' coliunn towartl the ventral L'ray cohiniii. \\K\uv of I hem eiilcrini;: and eiidinti; in this ])ortion of tlie cord. J'm.. 117. IIk (;,.l;iri,i, ,,,,-, ,,1 I ; ,-la tul . . /;- Tl ,|,,r-.'ll llnlll ('- I 'l:,rl.r\- r, ,1,11,1 I/— The v.'ii1ro-l:,h-.;il r, II ,,,!,, A'— Thr ,|,,r,,i,l I:, I, Till ll.lrrill r,|| -nl.M.-l.i I i!u- LiOiN IMiilliT uf llii- lli..l:i-ir Ivuh.M of ll:r ispillal rord. ■[.r.-.i-nt llir full,, unit' [■,,|l-,jr,, lip- : . I --Tlir rcll, of tho substantia. ■< r\ iriil iiiiil -iirnil iiurlri yl Stiliiii^ — llif iiicsial busal group of the Ji -I l,r M n[rn-iii'--i;,l i' 'll c ul LI III 11 . E — Tlic dorso-Hiosial Cell column. // — riir int. iiiiiiiiiitr ,lursn-lateral cell column. / — The central cell I. — I'lir liitiTiil ha,ii of Hie spinal coiyI sc.mnent imlii/atiii;; the gi-ay aiKl \N-hili' n.liuiiii.s, I In- uiit,i:nil m- dcir.siil ami tin- i'iiii'i'Ki;iit nr VL-nlral I'oot fil'Ofs, tlip liiji'SEil lYinl Li.'iMEiliciii .Yiiil tlir \ (-1111:11 i:i:i\' E'liliniui lYtl i;riMi]is. The \'enli-:d gr.'iy cohunn also coulains a. grou]) of cells ceiitiYilly pLiced and constiluling the ciidinl colninn. This nuikes i1s first appearance at the U])i)er liorder of the second iinnlior ■■^djnicnt. rcaclies i(s lai'gest. diameters in tlie _////// liunljor signicnl and ilisajipcai's al thi' Iowyt liord(.'r of tlie./(/'s< sncrid segment. Tnr:LATKH.\LSrL.\Nr]iN]c]\I(>Toii( 'ei>l (_'( iLT'MX. Another long column of cells making a jirotrusion into the whiti' mailer is the lateral horn, which is found at the junction of the vential giay cohunn with the liody of the gray substance. This is the loteral siijunclmic motor cell cohunn. The axoncs THE SPINAL CORD ■U from these cells make their way to the vegetativ(> sys- tem. The c.elLs ai-e stioho- chrome in form, of medium size, varying from 1 2 to (50 micra in diametei-. The lateral splanchnic motor cell cohimn makes its first appearance at tlie upper border of the jirKt thoracic segment, extends through- out the entire length of the thoracic segments, Ix^gins to diminish in the //r.si lumbar segment and disap- pears at the lowei- l)order of the second lumbar seg- ment. It makes its reappear- ance as a tliffuse group of cells in the second, third and fourth sacral segmenls. The Body of the Gray Substance. This structure contains a niun):)er of small groups of nerve-cells. These cells are most numerous in tlie enlargements, especial- \y in the cervical region , and least numerous in the thoracic portion of the cord. In addition to these scat- tered groups, there is a more definitel.y circumsciibed collection of cells situated in the l)ody of the gray matter which is known as the intermediate or middle nucleus. This extends ir- r e g u 1 a r 1 y through t he length of the cord ; its cells are larger, stain better and show the Nissl's bodies more l50R-50-ME5tAL n OTOR, CO LUM r DOR SO-neSIAL MOTOR. COLUMrr VCMTBO-f-IESIAL noTOR. coLunn VEnTR0-nE.5iAL rtoTOR coLunn DORSO-nESIA L noTOR coLunn VEriTKO-r-lESIAL MOTOR. coLunn Fig. 122. — A diagraninia.tie representation of the vovtical extent .and relative transverse proportions of tlic me.sial motor cell columns of tlic ventral gray matter of the spinal cord. The relative position of the cell cnlinnns in transverse section is in- dicated at the liiiht. 138 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM inTFFLMEDIATE POR50-LATECAL MOTOR. COLUnn VEnTRO-LATERAL MOTOR COLUnn DORSO-LATERAL MOTOR COLUMn inTERMEDlATE DORSOUTEfcAl noToct coLunn VEnTRO-LATEP.AL MOTOR. COLunri D0R50-LATECAL MOTOR. COLunn INTERMEDIATE DoeSO-LATER nOTOR coLUnr VenTRO-LATERAL MOTOR. COLUMn DOR&O- LATERAL MOTOR COLUMn clearly. A few of these cells send their axones to the opposite side by waj^ of the ventral commis- sure, but most of them arc directed to the lateral column of the same side, where they serve as as- cending and descending intersegmental associa- tion fibc]-s. The Dorsal Gray Col- umn. Several cell groups maj^ be identified in the dorsal gra>' column. The Base of the DuHS.lL ( 'tRAY C'(1LUMN. In the l.iase of this col- umn, whore it joins the liody of the gray sub- stance, there are two groups of cells, the lat- eral basal group and the iricsial basal (jroitp. The lateralhasal group is most extensive in the cervical region and is comprised for the most part of cells oi Golgi !tVtyiieII. The pyramidal axones seem to end al)out these cells, while their own axones go forward to the ventral horn. It IS possil.de that the cells of this group ser\-e as the short inter c a 1 a t e d neurones which relay im- pulses recei\'ed l»y way of the pyramidal tract to the root cells in the ven- tral gray column. Fig. 123. — A diagranima.tic reprcsenlation nf tlie \'er1iral oxlLTit and rrlative transverse proportions of the lateral motor cell ei>lurnns of the ventral gray niatter of the spinal cord. The relative position iif the cell columns in transverse section is in- dicated at the right. THE SPINAL CORD 139 The mesial basal group, aho known as the posterior vesicular column of Clarke, makes its first appearance in the Jirst lumbar segment, and extends without in- terruption up to and through the Jirst thoracic segment. It is best marked in the lower thoracic segments. A nucleus corre- sponding m position to that of Clarke's column is situated in the third and fourth lumbar and first sacral segments, and simi- larly a nucleus having the same topog- raphy appears in the cervical segments. These are known respectivelj^ as the sacral and cervical nuclei of Stilling. The cells, however, are different from those in Clarke's column, and a different physio- logical function is attributed to them. The cells of Clarke's column vary in size from 40 to 109 micra in diameter. They are multipolar elements whose axones extend outward to the lateral column of the same side. The nucleus as a whole and some of the cells in it are surrounded by a fine plexus of fibrils from the collaterals of the dorsal tract fibers and also from the lateral pyramidal tract. The cellbodies constitut- ing Clarke's column have certain peculi- arities which frecjuentlj'IeadtothelDelief that these cells are pathological. Nor- mally, however, tliey present a picture which closely resembles that of central chromatolysis. Their nuclei are eccentric- ally placed, the cell bodies seem somewhat distended, the Nissl's bodies are absent about the nuclei and appear onlj' along the peripheral border of the cells. Quite frecjuently the cells of Clarke's column lodge a considerable amount of fat pig- ment. Another peculiaritj^ of these cells is the fact that their dendrites are con- fined to this area of the column. Certain smaller cells have been observed in 1=^ 3 1 ■LATERAL 5Pl.AnCHnic .nOTOR. CELL COLUMn LATERAL SPLAnCHMIC 5 ;i CEnTR.AL noToR. CELL COLUnrN _S i ^ LATERAL 5PLAnCHf1IC ' nOTOR CELL coLunn S5 Fig. 124. — A diagrammatic representation of the vertical extent and relative transverse proportions of the lateral and central motor cell columns of the ventral gray matter of the spinal cord. The relative position of the lateral splanchnic cell column in transverse section is indicated at the right. 140 Forai and pi^n^'tioxs of the cKXTitAL nervot;s system Clarki'V I'oltuiin; these iii'c ,situate(l ai'duiid (lie |;ieM')")her>' of the Ki'oup ami ai'e kliiiwii as the liiiiitinij crlls iif Ciijiil nr (he tti iiiir/iliiil rrlls of LenJlOSScl:. These eleiiieiils \-ai'>' from 2") tn '-'A) iiiiera in (liaiiietei-. Tirj-: ('er\ix of Tnii Dorsal (!ray Columx. Una region eontains a siuall srcmp of stellate and spindle-shaped cells. These are often referred to as the Nolitari/ crlls of the dorsal horn, the axones of which extend to the ventral liorn nr (o the gi'aN' coininissui'e. SUBSTAHTIA GELATinOSA LATERAL BASAL COLUnn "-.^ ' , MESIAL BA6AL COLUMn LATERAL SPLAMCHniC MOTOR. CELLCOLUnn ■~-^ "-^ ; / D0R.50 -ME,5IAL MOTOR CELL COLUnM DOR.50"- LATERA^Lf^ MOTOR^ CELL COLunn, inTEPLMEDIATE ^ D0R60-LATER.AL MOTOR. CELL COLUnn VEnXRO-LATEftAL MOTOR, CELL coLurin VEHTRO-rlEilAL MOTO R, CE LL , - coLunn LATERAL MOTOR, , CELL COLUMn ' t«4tl^ Fir,. 125. — A ilia.;{r;uuiii;iti(; icjJie.sRntation of tin' spinal conl segment indicating tlie relative pusitiun and proportions of the Kia\' and white matter and the approximate position of the most important cell groui)S in tlie gray eolnmns. The Caput of the Dorsal v 1Iolaxd(l This contains many small scattered cells rich in dendrites. The axones of these cells pass to the lateral tracts along (he margin of the substantia or to larger stellate cells whose axones have I he same destination. The Gray Commissure. The cells m the gra>' commissure are small and medium-sized eoiiimissural cells. Idieii' axones extend in either direction toward (he lal ei'.al tract s. THE SPINAL COHI) 141 The reticular fonnai/on which, in the upper poilioii of the ccivieal region, appears to be continuous with the reticular formation of the nieduUa o1_)longata, contains large stellate cells with l^ranching dendrites antl axoncs which pass hy way of the ventral and dorsal conuiiissuivs into the lateral tracts. THE WHITE AIATTEK OF IHE SPINAL CORD The white matter of the spinal cord is so arranged that it forms a sheath about the gray matter, except m some areas opposite the dorsal gray column where the gray matter ajiijroaches the circumfeience of the conh The emergence of the ventral root fitters and the entrance of the dorsal root fibers serve to divide the white matter into three columns which are of topographical as well as physiological significance. The Dorsal White Column. The zone between the dorsal root fibers and the dorso-median septum is the dorsal column. It is made up of a number of conspicuous fasciculi. In tlie main, its function is sensor>'. The Lateral White Column. The second zone lies between the dorsal root fibers and the ventral root filiei's. It is the lateral column, which, altliough it contains a few fasciculi to sei've the purposes of sensation, takes its pliy- siological importance chiefly from the fact that most of tlie fasciculi in it furnish connections from the brain to the spinal cord. The Ventral White Column. The third zone is limited b>- the ^•entro- medial fissure^ and the ventral root fillers. It is the ventral column. Like the lateral column, it is largely motor in its function, serving to bring the sjjinal cord under the conti'ol of the higher centers. The composition of the various fasciculi which enter into these three columns follows a well establislied law. According to this law the bundles of nerve fibers in the white matter lying closest to the gray matter ai-e composed of axones whicli are relativeh' short or make a relatively short course, T\'hile the fasciculi farthest removed from the gray matter are nuitle up of axones running a much longer course either from aljove downward or m the reverse direction. DIFFERENCES I.\ THE CROSS SECTION APPEARANCES IN THE Si:VERAL DR'IsrONS OF THE SPINAL COED Cross sections illustraling the essential differences in tlie coccygeal, sacral, lumbar, thoracic antl cei-\-ic;d segments of tlie cord are sliown in tlic accompanying figures. Cross Section through the First Cervical Segment. The ciicuinference at this level of the spinal cord is oval. Tlie a^-erage diameters are: 1ians- verse, 8.3 mm.: dorso-ventral, 6.3 mm. The ^'■entral gray column is relativel>' small and ))\'nform m sliape. Th<' lateral gray column is present Ixit relatively- small. The di)isal gray column has a large amount of substantia gelatinosa. The neck and liody of the dorsal gray column are short and thick. The gray matter constituting the gray commissure is a large quadrilateral l)ody, \-entral to whicli is the white com- missure. Between the lateral gray column and tlie dorsal gi-ay column is tlie 142 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM CVrviral I. reticular formation, a prominent clement at this level. The ventral gra}' column and the dorsal gray column are about eriual in size. The dorsal white column on either side is triangular in outline and more extensive than in the lower levels. The lateral white column occupies the largest portion of the wliite matter of the cervical region, wliile the ventral white columns are relatively small and separated ]>y a deep ventro-median fissure. Cross Section of the Eighth Cervical Segment. The circum- ference at this level is oval, the transverse diameter being nearly twice that of tlie dorso-ventral, representing the greatest trans- verse diameter at anj' level of the cord. The average diameters are: transverse, 12.5 mm.; dorso- ventral, (5.5 mm. Tlie ventral gra}' column is large and presents a mesial and a ventral projection, each con- taining specialized cell-groups. Tlie lateral gray column is jii-omment and projects laterallj' for a consider- able distance. It contains an extensi\'e group of large nerve cells. The com- bined size of the lateral and the ventral gray columns is approximately five times that of the dorsal gray column. The suljstantia gelatinosa is much re- duced as compared with the upper cer\-ical levels. The area spongiosa is re- moved from the periphery by a considerable distance. The neck and liody of the dorsal graj' column are short and thick. The central gray matter is present in the form of a thin strand of commissural gra>- matter. It is more attenuated at this levfl than in anj- other seg- ment of the spinal cord. Tin' ventral white commissure is correspondingly small. Situatt'd between the lateral and dijrsal gray columns is the formatio re- ticularis, which is much reduced in size as com]iared with that of the upper cervical levels. The lateral white column is somewhat larger than the dorsal white column. The ventral white cdluiiins are separated ))y a deep and wide ventro-median fissure wliich, uiioii a.p])roa,ehing the ventral white commis- sure, bifurcates, (nie ]:)raiicli going to 1lie right and one to the left. Cross Section through the Eighth Thoracic Segment. The circumference at this level is nearly circular, the dorso-ventral diameter Iteing slighth' less than the transverse. The average diameters are: transverse, 7 mm.; dorso- ventral, 6.2 mm. Cervical VIII. THE SPINAL CORD 143 rhoracic VIII. The gray matter as a whole is smaller than in any of the other segments in the spmal cord. The ventral gray column is separated by a considerable distance from the periphery. There is a small lateral gray column. The dorsal gray column is narrow and tapering. It presents but a small amount of substantia gelatinosa which is removed from the periphery by a distance double that observed in the cervical region. The neck and body of the dorsal gray column are thick and longer than in the cervical region. The reticular formation between the ventral and lateral gray columns is feeblj' developed. The dorsal, lateral and ventral white columns hold relatively the same proportions as in the lumbar levels. Cross Section through the Second Lumbar Segment. The circumference at this level is oval, its transverse diameter being the longer. The average diameters are: transverse, 7.S mm.; dorso-ventral, 5.7 mm. The ventral gray column is relatively large and irregular in outline. The dorsal gray column shows a marked increase in the substantia gelatinosa of Rolando and presents a short neck and body. The entire gray matter gives the impression of having been compressed dorso-ventrally. The gray commissure is short and thick. Ventral to it is a massive white commissure. There is no lateral gray column. The reticular formation is feebly developed. The dorsal white column is larger than the lateral white column, while the ventral white column is relatively small. The ventro-median fissure abuts by its dorsal extremity against the white commissure. The dorso- niedian septum is separated from tlie ventro-median sulcus by the slight distance corresponding to the width of the central gray matter and the ventral white commissure. Cross Section through the First Sacral Segment. The circumference at this level is oval and shows the greatest prominence in the ventral quad- rants. The average diameters are: transverse, 7.9 mm.; dnrso-ventral, 5.8 mm. The ventral gray column is large and is divided into a mesial and a lateral cell group. The dorsal gray column is likewise large and removed Fio. 129. — Lumbar 144 FORM AND FUNCTIOpviS OF THE CENTRAL NERAOlS SYSTEM Fic. 1:;G.— Cervical \U. Fig. 1:J0.— Curvical I. Fic. i:jJ.— Cervical K. Fic. 1:;i:.— <'cr\-ical HI. Fill. Vi'A. — Cervical W . Fjc. 1^7.— Cervical VIIF Fic. 1:;.\— Thnracic L Fic. urn.— Tliciucic IF Fic. 1:M.— CiMTical \". FiG. 140.— Thoracic IIF Fic. 1:;.1— Cervical VF FiG. 141. — ihoracic H. THE SPINAL CORD 145 Fid. 143.— Thoracic Vl. Vic. 144.— Thoracic \'I1. Fid. 145.— Thoracic \TI1. Fi(,. Ufi.— Thoracic F\. Fio. isn.— Lumbar I. I-'io. 147,— Thoracic -\. Fio. l.").'i. — Fuiiiliar I\' 146 FOEM AM) FT'XCTIONS OF THE CENTRAL NERVOUS SYKTEM Fit;. 154. — Lumbar V. 155. — Sacral I. Sacral III. Fig. 15S.— Sacral IV. Fig. 1.5r,.— Sacrnl TI. Fig. 1011.— C'ocrvKcal I. but a small distance from the ]K'riplicTy. Tlie sul)staiitia gelatinosa is larger here than in the lumliai- st^gment. There is no appreciable neck or liody in the dorsal gray column. The central gray matter constitutes a thick com- missure, venti'al to which is the white commissure. The reticular formation is feebly developed. The dorsal white column is still somewhat larger than the lateral white column, while the ventral columns are smaller than in the higher segments. All three columns of the white substance are relatively small. Tliere is a consideral)Ie increase in the size of the gray matter. The ventro-median sulcu.s is separated at its dorsal e.xtremity of the ventral extremity of the dorso-median septum by the distance correspond- ing to the widtli cif the central gray matter and the ventral white commissure. THE SPINAL CORD 147 Cross Section through the Fourth Sacral Segment. The circumference at this level is oval, the greatest diameter bemR- transverse. The avr.rage diameters are: transverse, .5.3 mm.; dorso-ventral, 4.0 mm. " ' The ventral gray column is large, and its entue circumference is but little removed by the intervening white matter from the circumference of the segment. The dorsal gray column is also large, approaching the sizeV.f the ventral gray column. It presents neither body nor neck and passes with- FiG. Itil.— Sacral IV. out line of demarcation into the ventral gray column. The central gray matter is large and lies about midway between the dorsal and ventral sur- faces of the cord. Ventral to it is the large white commissure. The dorsal gray column is but httle separated from the periphery of the segment. The reticular formation is feebly developed. The distance between the ventral and dorsal gray columns is slight because of the small amount of intervening white matter. Each of the three con- stituents of the white substance, the dorsal, lateral and ventral white columns, is relatively small. Cross Section through the Coccygeal Segment. The circumference at this level is irregularly oval, its greatest diameter being dorso-ventral. The avei'- age diameters are: transverse, 2mm.; dorso-ventral, 2.2 mm. The ventral gray column is small, about one- half as large as the dorsal gray column. The central grajr matter is also of small dimensions and the two bilateral masses of the graj' matter are in close relation to each other. The reticular formation is feebly developed. A small ventral white commissure lies in front of the central gray matter. The dorsal ventral white columns are just beginning to appear. The largest constituent of the white matter at this level is the lateral white column which consists chiefly of the pyramidal tract. The descriptions of the cross sections at these several levels represent the decisive changes from one division of the spinal cord to the next. Fig. 162.— Coccygeal I. rHAPTKi; X THE SPINAL fORD THE FUNCTIOX '|)e; they vary much l)otli in size and structure, and this fact seems to justif\' the sujjposition that they ilo not all manifest the same functional ,acti^'it^'. FX'NCTIOX OF rili; \U;X-|HAI, SOMAI'lC MOTOH COLIMX The cells in the A'entral gra\' colunni ai'e lai'gi', slichochrome elements, while the cells in (he doisal gra>- colunm are smaller and ha\'e a much less definite arrangement of tlieii- Xissl's bodies. Laige stichoclironie cells at once suggest motor function, ami for this reason the \-entral gray <'oluinn i.s regarded as essi'rdial io the inotoi' imiiuls(-s which activate' the executive organs of the l)ndy, the muscles. The iloi-sal gray column is, in the main, sensory in its t>'pe of function, and here man\- of the ini))ulses coming from the various rece])tors are recei\-ed aii' column, on tlie other hand, is not exclusi\-e]\- sensoi-y in its acti\uty, but serves the many purposes of intrasegmental and suprasegmental association. The body of the gray matter, as widl as tlie gra>- comnuMsure. :dso ser\-esin tliis capacity of association. The largei' cells in the \'entral gray ccf intervention of the ventral column cells. Idiodynamic Control. The control which the A-entral column cell exerts ovei' the muscles is found u|)on analysis to lie com])lex. In tlie first place, the health and normal activity' of tlu* skeletal muscles is dependent upon 1 IS THE SPINAL CORD 14i) th(.\s(' ventral column cells. Disease or destruction of thenr means impaii'- ment or disintegration of the muscles. The control of the muscles, in all their complex activity, is vested in the cells of the ventral gray column. These cells exercise; a remarkable influence upon the life and maintenance of the muscle fiber as contractile tissue. When the muscle is deprived of this fundamental control, it ceases to live as muscular tissue and tends to revert to the simpler elements with which it is genetically related, the con- nective tissue. When the ventral column cell is injured as a result of disease or accident the muscle at once shows the effect of this alteration, not only in the loss of its contractile power, but by an at^tual diminution in its volume. Paralysis and atrophy, tlierefore, ensue when the motor nerve cell is thus affected. The atrophy or loss of volume is mucli more serious than a mere decrease in the size of the muscle fibers. It results in an actual solution of the contractile substance and the final replacement of it b}- fat and con- n('Cti\-e tissue. This process is spoken of as muscular degeneration, secondary Ventral Gray Column Cell Dorsal Spinal Ganiihon Cell Fig. Ujo. — Tlic final common ])atlnvay. A — Llioilvliamic control. Fii>. IGl, — The final common pathway. A — iiliodynamic contrul. B — Intraseg- nicntal reflex aliil tunic control. either to involvement of the ventral column ccU or to an interruption in its axone connecting it with the muscle. This influence which the cell has over the muscle fiber appears to arise within the cell body itself and to be inde- pi^ndent of all other sources of nerve impulses within the nervous system. By means of the galvanic current it is possible to determine whether the nmscular tissue is held in its normal control or to what degree this control is impaired. The normal muscle when stimulated l)y the cathode of the galvanic current shows upon closure (K.C.t\) a much more active contraction than when stimulated by the closure of the anode (A.C.C.). This reaction, indi- cated by the expression K.C.C. greater than A.C.C., is the ncjrmal galvanic contraction formula. When the muscular tissue has been deprived of its control by the ventral column cell, this formula is reversed so that A.CA'. becomes greater than K.C.C, which expression represents th(> reaction uf degeneration (R. D.). The un.supplemented influence exerted liy the motor nerve-cell directly upon the muscle is known as idiodynaniic control of the ventral gray column. Reflex and Tonic Control. The ventral column cell sends out many impulses to the muscles which differ materially from those essential to 150 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM idiodynamic control. Numerous connections are established between the ventral column cell and other parts of the nervous system. One of these connections brings about a relation with the dorsal root ganglion cell in, su(dr a way as to consummate a neural arc. This arc has its beginning in a receptor somewhere near the surface of the body, continues inward through the peripheral process of the dorsal root ganglion cell, i-eaches the spinal cord l)v way of the c(>ntral process of this cell, and by means of a collateral from its axone, completes the connection with a cell in the ventral gray column, thus bringing the motor cell under the influence of impulses arising outside of the nervous system. Such impulses as are conveyed from the surface liy means of the dorsal root ganglion contribute in an important manner to the activitj' of the motor cell. A constant flow of stimuli is transmitted to the nuiscle and serves to maintain the muscular tissue in a definite state of contraction, known as myotonus. In consequence of this reflex connection, the muscle is subject to another variety- of regulation called rejlcx control, whicli regulates reflex action. This phenomenon results from the stimulation of certain end-organs related to the muscle, particularly those organs which are located in the skin or in the ten- don of the nuiscle. A good example of such reflex control is afforded by the biceps muscle which upon percussion of the biceps tendon contracts and thus produces a muscular response called a reflex moremcni. The most classical of these movements is elicited by percussion over the patellar tendon, in response to which the quadriceps extensor muscle con- ti-acts forcil)ly and produces an extensor movement of the leg upon the thigh. This is the patellar reflex. It is dependent upon the stimulation of the recep- tors in the tendon spirals and the transmission of the stimulus by means of the dorsal root cells to the ventral gray column cells. These impulses stimulate the motor cells, and in consequence there develops in the muscle a rapid tonic contraction followed by immediate relaxation. By means of the con- nection with the affei'ent element of the dorsal root ganglion, the motor cell in the ventral gray column is enabled to (wert myotonic and reflex control over the muscles. Should this cell become impaired or destroyed, myotonus as well as i-eflex activity cease in the corresponding muscular tissue. This direct connection Ijetween the receptors and the motor cells in the ventral gray column constitutes the simple reflex arc: The motor responses deter- mined by simjile reflex arcs are represented l)y simple reflexes known as reflex acts. Segmental Associated Control. The muscles of the body are made up of collections of muscle fibers, and the control of any one muscle is dependent upon the integrative or combined action of a numlier of nerve-cells. In order that these cells may cooperate adequately, it is necessary that a connection be established between them, so that an impidse arising in one cell may simultaneousl.v stinuilatc all of the other cells normally associated with it. The motor cells of the ventral gray column are brought into such associative cooperation. AVhen the cells controlling a given muscle lie wholly within a single segment, they must all be lirought into action. This is known as THE SPINAL CORD 151 intrasegmental association. Each cell in the ventral gray column is capaljle of forming many such associations through its dendritic processes. A motor act may require the contraction not alone of a single muscle, but of a group of closely related muscles whose contraction must be simulta- neous in order that the act may be accomplished. Motoi' cells controllmg all the muscles involved in such an act may occupy a number of neighboring segments of the spinal cord, so that it becomes necessary to associate all of them by a system of intercommunication. This type of muscular activity is made possible by means of intersegmental association. In this manner the motor cells in many segments of the cord may unite in the simultaneous dispatch of impulses to a group of muscles whose action gives rise to a defi- nite performance. Intersegmental Association Cell Doraal Spinal Ganglion Cell ^'ent^aI Gray Column Cell FiQ. 165. — The final common pathw.-iy and its control: A — Idiodynamic control. B — Intrasegmental refle.K and tonic control. C — -Intersegmental reflex control. In many instances it is necessary for the segments to cooperate with each other, not merely as a longitudinal series upon the same side, but in such a way that the muscles upon one side of the body may perform acts simul- taneous with those upon the opposite side. When such a combination is ac- complished, it is by means of a transegmental association. This tj'pe of asso- ciation may be confined to a single segment, or may bring several related segments into associated activity. The motor cell in the ventral gray column dispatches all of those impulses which it receives from other sources whose combination results in segmental associated control. Vestibulo-Equilibratory Control. It is not alone from the spinal cord and the dorsal root gangha that the motor cells receive the impulses which modifj^ their activities. Impulses of much importance reach them from dis- tant sources and from organs whose functions contribute to the regulation 1.V2 FDini AND fi:n(;tioxs of the central XEin'ors system of motor acti\'i(y. Sucli arc the impulses which come to tlie motoi- cell fioni the vestibule of tlie internal ear and particularly- from the semicirculai- canals. These i)ortions of the Itody are etpiipped with special receptor's whose function it is to receive stimuli essential to static and dynaniic equilihiium. The scMnciicular canals, according to the best in1erpi-etatio)i Cell of Deiter's Nucleus Cell of Scarpa's Ganglions lilur Canal, Dor: oalCaugl lijlfr^ctrmoiital AsMiciatinn ('< al Gray Coluini, Cell I'lG. lIlCi. — The fiiiiil i-oiiiiiiiiii ii;illi\v;i\- ;iiid its cuiilrul: ,1 — Jdiochiuimic cuntrol. B — Intias^cninciilal rr-flcx and 1i)nic roiitii.l. C — liitorsc.siiiciital reflex cimtrdl. D — Equilibratory control. 1)' — Primary vestibular neurone. (d' llicii' siKnifi<-ancc, iila>" an iiii|iort,ant role in the maintenance (d" boily e(|uilibrium durinji, locomotion, while the utricle and saccule seem to lie ilcsigned for the )mri)Ose of liody balance in standing or sitting. Either one or l)oth of these mechanisms may lie so distiu-bed as to make the l)alanciiig (d' the l)ody difficfdt or impossible; in that event the pati(>nt shows a stagger- ing in his gait or a swaying in his station, and,rniless sujiported, may even lose his l)alanc(> altogether. The stinudi received by the vestil)ular jxirtion (d' the intei'nal ear are ti'ansmit teii to Deitei-'s nucleus in the metlulla oblon- THK SPINAL rOKU 153 R-ata, and fi'oni this relay station tlic iiupulses arc dispatched to tlie nileus^ _ -- Cell of Scarpa's Cunglion^ Semieireular Canal: ■Jiujeiilal Assoeiation Cell Dor.sal Spinal Clanglion ( '.1) liuiiD Cell Fi(i. 167. — The final comniDii patlnvay: A — Idiodynamic contfol. /)' — Iiitrasegmental reflex and tonic contml. C — Intersegmental reflex ccmtrol. 1) — Kquilibratorv control. D' — Primary vestilnilar neurone. E — Synergic control. E' — Dentato- rubral neurone. beilum enters into this function to a marked degree, but it is also <'lear that the connection between the semicircular canals, the utiicle and saccule on the one hand, and the motor cells of the spinal cord on the other, maj^ be aecomphshed directly without the intervention of any other oi'gan. The significance of the vestibulo-equilibratory control will lie discussed more in detail in a subsequent chapter. 154 FORM AND FUNCTIOXS OF THE CENTRAL NERVOUS SYSTEM Synergic Control. In all the iierfoniiances of the skeletal muscles, in every act producing movement in a joint, a universal principle of coordina- tion may l>c observed. The mus<-les of the Ijody are so arranged that each individual nuisclc or each si.iecialized group of muscles has its particular an- tagonistic group. In the arm, the triceps is the antagonist of the biceps during movements of flexion, ami in the reverse order, during move- ments of exleusion, the biceps Ijccomes the antagonist of the triceps. These ajjparent antagonists, ho\ve\-er, are such in the morphological sense only, because they are by th(>ir jiositions opposed to each other. Physiolo- gically, they act together and simultaneously. During flexion of the forearm upon the arm, the hiccjis not onlij eontrocts sufficiently to produce the motion of flexion, but the triceps also contracts to determine the degree and the rate of this flexion. In other words, the triceps acts as a check against the determinant motor force producing flexion. Similarly, when the arm is extended, the biceps liecomes the check element against the action of the triceps. Biceps and triceps are, therefore, <'onstantly working together and constitute a synergic unit. In this manner muscles of the body are arranged in groups of s>-nergic units. If there is a disturbance in the synergism which normally exists in each synergic unit, the movements produced by such muscles become irregular and abnormal. The check element is not properly proportioned to the requirements of the deter- minant element, and a movement under these eonrlitions becomes greater than its purpose requires. This makes necessaiy an over-correction on the part of the check element, which in turn is also in e.xcess of the requirements of the niDVcnient. The motor act in consequence manifests a series of irregidar (jsrillations; it loses the directness and precision which are char- acteristic under normal conditions. When such a disturlxmce exists, it is called incoordinutiiui or ataxia. The proper regulation of the synergic units of the body is the special function (jf the cerebellum. It is possible that other portions of the Ijrain enter into this important type of motor control, but there can be no rpiestion that tlu^ cerebellum is fundamentally concerned in this activity. By means of a connection with tlie cerebellum, the motor cell in the vrnfral column is capal)le of distributing impulses whose pur- pose it is iiit, autoiuatic association appears even in man. E-veii thouiili the ai'ins have been i'reed fi'oni actiial participation as ( VII of Sur C,.]\ Mf D.HtiJtr X Cell o[ Scaijiii's < SeliiiriiTiil;u' ( 'ana Dorsul Spinal C;a]i;^Ii(.,i, ("dl Cmljus Striatum of Corpus Striatum d Nucleus I '.-ll r,l Heifer's Xuel,.u^ iuter-ei^ mental _\ssoeiation { ell I'll;. 169, — Tlii-tijinl criiiiiiM.ji )i;i(]i»-.-i\- ,■111(1 its coiitixil: .1 — ttJioilyiiMiiiii- control. Ji — Iii- (lasfginciitul icllcx ami tcriii- (■(nilriil. (' — Ji]t('i-scK'i'i''nf al letlex ri>iitiT>l. J) — Eqiii- librtitoi-y control. />'- -Priiii:try \c,stil.)ulai neiiioiir. E — S,\iiergic control. E' — Drii- tato-ccplialo-gyric (amlrol. /•' — Oiailtj-ocphalouyric control. open to dc- THE SPINAL CORD 157 I'ate, the fact i-emaiiis that in certain diseases in which ck^generatirm aifects the corpus striatum, the mcst marked - and itscontrul: -1 — Lliiiil.\iianiic fonlrol. /; — In- trascgniental reflex and tunie eoiitfid. C — Jntefsegniental reflex eitnti'ol. /; — Eqiii- libratory control. D' — Primar\' \-e.stibiilar neurone. E — Synergic ODritiol. E' — Dentato-riibral neurone. F — Oeulo-eephalogyrie control. '/ — .\utomatie associated control, f^/' — Striato-mliitil neuio]ii\ // — Voluntary control; inhibitory control, tlie more or h\ss comjilete sui")])ression of automatic associated actions. The many f[uestions arising in connection with this ty])e of motor control will besubsef|uentl>'discussefl in the chapter dealing with the corpus striatum. 158 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM In order that the impulses necessary for the automatic associated con- trol may reach the muscle, the motor cell in the ventral gray column must establish a connection with the part of the brain in which this function is vested. It seems probable that impulses of a similar character, particularly associated with the visual function, may make their way to the motor cells and thus to the muscles. Such associated automatic acts based upon sudden extreme stimulation of tlie retina would be in the interest of protecting the eyes by associated movement of the arm and head. For example, in the pres- ence of a blinding flash of light not merely are the eyelids tightly closed and the head flexed far forward, but the arm is automatically raised to shield the retina. A connection exists between the roof of the midbrain and the motor cells in the spinal cord and brain stem. This connection is known as the tecto-spinal tract. It un(.loul)tedl3r affords the liasis for the production of associated automatic acts of the eyelids, ej'es, head and arm in a defensive mechanism to protect the retina and eye. Voluntary or Volitional Control. The skeletal nuiscles are capatile of producing long and sustained series of actions under the direction of the wiU. These actions are usually referred to as voluntary, because they are initiated and inhibited by volition. They differ from the automatic associated action in that they are acquired l.iy means of individual experience. The muscular combinations and control necessary for their execution are not inherited, but are learned as the result (jf a s1(jw and long process of repeti- tion. A good example of such tj'pe of motor activity is afforded by handwrit- ing, a skilled act which is acquired only after a tedious process of repeated efforts and persistent concentration of attention. The impulses of this voh- tional control arise in a certain area of tlie cerebral cortex known as the Rolandic or motor area. This portion of the brain contains many large pyram- idal cells whose axones run a long course through the lirain .stem and spinal cord; these are the pyramidal fibers which eventually bring the impulses of volitional control to the motor cells of the ventral gray column. In addition to this regulation of the cerebral cortex there is a tj-pe of cortical control, as yet not altogether clearly understood, which exerts an inhilntory in- fluence upon the motor cells of the spinal cord. This inhil.)itory influence makes itself apparent primarily in the tone of the muscles, for when the pyramidal cells of the motor cortex are delivering their impulses in a normal manner, the tone of the skeletal muscles is such as to adapt the muscular tissue most readily to the purposes of volitional action. Such a state of mus- cle tone vaay be called the ideal muscle tonus, because the muscle is neither too much contracted noryet too nuich relaxed, but is in the tonic state, some- where between these two extremes, best fitted to respond adequately to the dictates of the will. A muscular system which is too greatly contracted would of necessity respond slowly and in a rigid manner, while a muscular system too much relaxed would require an unnecessar}' amount of motor stimula- tion. This ideal muscle tonus is dependent upon the connection between the lirain cells in the motor cortex and the motor cells in the spinal cord. When the connection between tliese two is interrupted or destroyed, the patient not THE SPINAL CORD 159 only loses the power of volitional control of the muscles in the parts affected, but the muscles themselves lose their ideal state of muscle tonus and mani- fest, in marked degree, a tendency to become unusually contracted. Exces- sive myotonus may be so extreme as to produce malattitudes in the limbs, drawing the forearm up into sharp flexion upon the arm, flexing the wrist upon the forearm and the flngers upon the hand. The leg may be affected in a similar manner. Such marked increase in tone, known as hypertonicitii or spasticity, is accompanied by an increase in the reflexes of the affected parts. It would seem, therefore, that the influence of the motor cells in the cortex of the brain serves not only to maintain the ideal muscle tone, but also to pre- vent the reflexes from assuming more than their normal activity. Other parts of the brain also exert an inhibitory influence upon the motor cells of the spinal cord, particularly the corpus striatum. In certain diseases afl'ecting this region, the muscles become hj-pertonic and the body is held in a rigid, almost inflexible position. The corpus striatum, therefore, not only provides an automatic associated control but also applies to the motor cell of the spinal cord a certain degree of inhibition in the regulation of muscle tone. The cerebeUmn must not be overlooked in this connection. Its influence upon myotonus, however, seems to be different. When the cerebellar connection is injured or interrupted, the muscles, instead of becoming hypertonic, according to certain authorities show some diminution in tone. This condition is known as hypotonus. It is probable that the reflex activities over which the motor cells in the spinal cord preside are influenced from at least four different sources: First, from the dorsal root ganglion, by means of which the motor cell establishes its simple reflex connection with the muscle. When this connec- tion is broken the reflex activity is abolished. Second, from the motor cells of the cerebral cortex which normally inhibit the activities of the simple reflex arc and maintain the muscles in a state of ideal muscle tonus. When this connection becomes injured or inter- rupted, the reflexes are increased, as is also the muscle tonus, giving rise to a state of hypertonus. Third, the motor cells in the corpus striatum so influence the motor cells in the spinal cord as to inhibit myotonus without affecting reflex activity. When this connection is injured or interrupted, the muscles be- come markedly hypertonic but the reflexes show httle or no change. Fourth, the influence of the cerebellum upon the motor ceUs of the spinal cord seems to be in the interest of maintaining the myotonus as well as the reflexes. Some authorities question this influence of the cerebellum. Influences Affecting the Ventral Gray Column and their Possible Defects. It will be seen that the motor cell m the ventral gray column receives impulses from many sources outside of itself. In addition to this it is pos- sessed of an intrinsic activity upon which the integrity of the muscular tissue as such, depends. The motor cell in the spinal cord in this hght may be hkened to a reservoir receiving supplies from many different areas but delivering them all to one common destination, the muscles. For this K.iO FOiat A.\l) FIXCTIOXS OF THF CENTRAL NERVOU.S SYSTEM irasoii the iiioloi' cell (il tlic spinal cord lias conic to he known as ihv Jiiki I coiiunoii iiiillni'iii/ of 1hc motor system. ]iy means of these cells every iin- l)ulse necessary 1o the coiiiplex requirements of motor activity in the skeletal muscles is ultimately t ransmitteij. Idiodi/ivxinic control, reflex anil liiiiic conlriil, sctjiii-eiiiol ronlrol, rrsl/hijlii-fi'/uilibratonj control, synergic (■(introl. oiildiiKilic o.^xiiciiiUil caiilrol iinil rohlKin.'i.l control, depend upon the motor cells in the s]iinal cord for I heir conduction to the muscles. When the cell itself is destroyed, the muscle fiber supplied 1j\' it is de- prived of iis idio' musculature regulatiuK the vital process. yet to be demonstrated. That these cells come under the influence of th(> cerebral hemispheres cannot b(^ doubted from the evidence of (dinical <>x- perience. The (lca;ree to which mental disturbances, such as anxiety and fear, may influence the cardiac action, the digestive movements of the stomach and intestines, and the reactions of the muscular coats of the blood vessels, IS too well recognized to be disputed. By what part of the brain and by means 162 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM of what connecting fibers this cerebral influence is exerted, remains to be determined. Differences in the Activities of Skeletal and Smooth Muscles. The control exercised by the lateral splanchnic motor column over the smooth musculature differs in another respect from that of the somatic motor con- trol. In the smooth muscles the contractions tend to be constant; at least the major portion of this musculature in its distribution throughout the body presents an unceasing and persistent activity. There are no long, irregu- lar intervals of rest such as is the case with the somatic muscles. The bulk of the splanchnic muscles, as for example in the heart and walls of the blood vessels, is continually in action. The type of this action is also a distinguish- ing feature; with few exceptions the character of the movement controlled by the lateral splanchnic motor cells is pulsatory and consists of a regular, uninterrupted series of rhythmical and alternating contractions and relaxa- tions. This is true of the peristaltic movements of the gastro-intestinal tract, the pulsation of the heart and blood vessels, the respiratory contractions of the branchial tree and the rhythmical contractions of the genito-urinary tract, including the ureter, the Ijladder and the uterus during the menstrual period and in labor. It is possible that this pulsatory character is imparted to the imjiulses arising in the lateral splanchnic motor cells by virtue of the connection with the ganglia of the ganglionated cord in the sympathetic S}'stcm. The splanchnic motor cells in the cord, like the somatic motor cells, are acted upon by afferent impulses. The stimulation of the mucosal surface of the stomach and intestines by the presence of food or foreign bodies, toxins or gases, will exaggerate the movements of these organs. The exact position of the fibers forming this afferent connection with the lateral splanchnic motor cells is not yet clear, nor are all the possibilities of chemical and other stimulation of these cells at present thoroughly appreciated. A highly specialized group of the lateral splanchnic motor cell column, in the cervical region, contributes axones to the formation of the spinal acces- sory nerve which sends its fil)ers out to supply the trapezius and the sterno- cleido-mastoid muscles. Both of these muscles are skeletal in character, and this innervation would, therefore, tend to controvert the principle that the lateral splanchnic motor cell column supplies smooth muscles. This excep- tion is of much importance. It will be seen later that these muscles are in part derived from the gill apparatus. The portions of these muscles having this derivation may lie regarded as muscles which are fundamentally of the visceral type. In the process of adaptation they have become greatly modi- fied and finally present the characters of skeletal muscles. The column of cells situatetl in the position of the lateral horn, through- out its entire extent contains cells whose axones innervate the glandular tis- sue of the body. The control of the glands, like that of the smooth muscles, is accomplislied thi-ougli the intervention of the sym|)ath('tic system. THE SPINAL CORD 163 FUNCTION OF THE DORSAL ROOT GANGLION CELLS The cells of the dorsal root ganglia are to be regarded as intrinsic portions of the gray matter of the spinal cord. In the early stages of devel- opment they are contained within the cord and subsequently migrate from it to assume their ventro-lateral position in the intervertebral foramina. In some lower forms, particularly in amphioxus, these cells never leave the spinal cord. This is a fact which gives further reason for regarding the dorsal root ganglion cells as integral portions of the gray matter. Although the cells vary somewhat in size and in the complexity of their axones, they are unipolar and present no dendritic processes. Their axone is T-shaped. It sends one process out peripherally and the other centrally to establish connection with the spinal cord. According to the arrangement of their Nissl's bodies, these cells are considered as gryochromes. Their function is sensory; they serve to receive and dispatch to the central nervous system all the sensory impulses which collectively enter into somesthetic or body-feeling sensibility. That there are cells in each dorsal root ganglion designed to receive impulses from the viscera and thus contribute to the forma- tion of splanchnesthetic or visceral sensibility is a debated question. Some authorities believe that the afferent fibers from the sympathetic system which serve to conduct such impulses from the viscera to the dorsal root ganglia, have no cellular elements of their own in these structures. This idea appears improbable in view of the structural plan of the nervous system whose general character would seem to justify the belief that splanchnesthe- tic sensibihty is provided with cellular elements in the dorsal root ganglia similar to those serving for somesthetic sensibility. The sensory cells of the dorsal root gangha receive and transmit the several different qualities of sensibility as follows: 1. Tactile sensibility ithigmesthesia). 2. Muscle sensibility {myesthesia). 3. Joint sensibility {arthresthesia). The muscle and joint sensibilities com- bine and thus give rise to deep sensibility {bathcsthesia). 4. Vibratory sensibility (pallesthesia). 5. Temperature sensibility {thermesthesia). 6. Pressure sensibility (piezesthesia). 7. Pain sensibility {algcsthesia). FUNCTION OF THE TRACT CELLS IN THE SPINAL SEGMENT Scattered tract cells in the dorsal gray column of each spinal segment serve to transmit to the brain the impressions which have to do with temperature sensibility. They also transmit to the cerebellum impulses received from the muscles in the interest of synergic control. The tract cells in the mesial basal nucleus of the dorsal gray column (the column of Clarke) are concerned m transmitting impulses from the muscles to the cerebellum also for the purposes of synergic control. 11)4 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS STST EM CSV nv Parieto-auriculo- mentat Line Mammarv Line Anterior Axial Lina Xiphoid Line mbihcai Line External Ax.al Line Fifi. 172.— The sonintic r(l Cervical . Posterior branch of 3rcl cer- Dorsal surface of neck from Dorsal vical nerve. inferior curved line to 3rd rervical Sjjincjus process. 4tK Cervical Supraclavicular and su])ra- Covers shoulder as far out as Ventral acromial branches of su|ier- junction of upper and mid-i ficial cervical plexus. die third of deltoid muscle. 4th Cervical fth Cervical Posterior branch of 4th cer- ' Small area between the pari- Oorsal vical nerve. ; eto-acromial lin<.' and inter- i ! scapular triangle. i Pavieio-ay'cnlo- Tiental Live -n — -- _T«5 ^-Cld — - - - C2d - C2V Par _eIo da roni il_Line '- - cjd -' - - C3V - C5a -- -^> ■^^ - ^- c cd -<.==^ ^ ■ \ — C'+ V C?; S^ >^~- y — T 1 d ^~\ -7 V\\. V-ced / A ft 7 -Tid I -Tid r-TiV [ TiV Firi. 17.5. — Facio-cranio-rerxiiMl dcriiia tonics. PoslenorAxial Line Acromio-trochdTiferic Line Fn:. ITii. — Interscapular triangle. \ Mltll.l \T.>w P03rer^r_A*ial Li^e AjileTior Alual Linp ),at..-n,l \lru- I>-.i.,i,l \ irw FiG. 177. — Fil'fh ci'iv'iiMl ili'iiii Mesial Viuiv THE SPINAL CORD 169 Dermatome ot.h t'crvical Ventral oth Cervical Dorsal 6th Cervical Ventral Gth Cervical Dorsal Nerve or rierves to which this are of innervation corresponds Area supplied by dermatome and general landmarks in its topography Dorsal nerve root corres- ponding to dermatome Anterior branch of the cir- cumflex, also its lateral brachial cutaneous branch. Posterior branch of oth cer- vical nerve. Middle third of arm, radial side from anterior to pes- ' terior axial lines. i.jtli Cervif.al Apex of interscapular tri- angle. External and internal I Lower third of arm from an- liranches of radial nerve, i Anterior and posterior ter- minal braiMjhes of musculo- i cutaneous nerve. Anterior terminal branch of radial nerve. Posterior branch of Oth cer- I vical nerve. terior to posterior axial line on radial side, also forearm on same side and hand as far a.s first phalanx of thumb. Interscapular triangle. titli Cervical C6d Posterior A»ial " Line C6V Ventral View ■ Lateral View Dorsal View Fig. 178. — Si.xth cervical dermatome. Po-.lrr.Or - AxialLinc N'entral \iew Lateral View Dorsal View Fifi. 179. — Seventli cervical dermatome. AvVaT Line MesKil ^'ie\v 170 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Dermatome 7th Cervical Ventral 7th Cervical Dorsal Sth Cervical Ventral Sth Cervical Dorsal Xerve or ner\-e3 to whieh thi;: area of innervation corresponds Area supplier! by dermatome and general landmarks in its topography Dorsal nerve root corres- ponding to dermatome Posterior external cutaneous Narrow zone surrounding 6th branch of musculo-cuta- neous nerve. Palmar cutaneous branches of median nerve and in- ternal and external terminal i branches of median nerve. Posterior branch of 7th cer- vical nerve. cervical dermatome. Covers dorsum of thumb, index, mid- dle and ring fingers in part. 7th Cervical Interscapular triangle. Terminal brandies of the musculo-cutaneous nerve, collateral branch of the ul- nar nerve, internal terminal branch of median nerve, external superficial palmar branch of ulnar nerve. Posterior branch of Sth cer- vical nerve. Covers anterior and posterior ', surfaces of forearm and a longitudinal zone on hand including index, middle, ring and little fingers, dorsal Sth Cervical surface of ring and palmar surface of little fingers. Interscapular triangle. Anterior Altai Line Vencrai V Lateral \ Dorsal \'iew .Mesial \'iBW Pia. ISO. — Eightli cervical dermatome. Antenqr Axial Line Ventral View Posterigr Axial Line Tid Tiv Tiv Dorsal View Fig. 181. — First thoracic dermatome. Mesial \'iew THE SPINAL CORD 171 Dermatome Xerve or nerves to which this area of innervation corresponds 1st Thoracic Ventral 1st Thoracic Dorsal Communicating branch with the intercosto-hum eral nerve, middle brachial cu- taneous nerve, terminal branches of musculo-spiral nerve, dorsal cutaneous branch of ulnar, collateral branch of ulnar and the superficial palmar Vjranch of ulnar. Posterior branch of 1st thor- acic nerve. Area BuppUed by dermatome and general landmarks in its topography Covers ulnar surfaces of hand, forearm and lower third of arm, in latter area extending from anterior to posterior axial lines. Interscapular triangle. 2nd Thoracic Anterior and perforating Fir.st thoracic zone with pro- Ventral ' branch and intercosto- longation into postero-in- ternal surface of arm. Ven- tral landmark, sternal in- sertion of 3rd rib. Dorsal landmark, 1st and 2nd thoracic spines. 2nd Thoracic Dorsal 3rd Thoracic Ventral 3rd Thoracic Dorsal branch and intercosto- humeral branch of 2nd intercostal nerve. Posterior branch of 2nd thor- acic nerve. Anterior and lateral perfor- ating branches of 3rd in- tercostal nerve. Posterior branch of 3rd thor- acic nerve. Dorsal nerve root corres- ponding to dermatome 1st Thoracic 2nd Thoracic 4th Thoracic Anterior and lateral perfor- Ventral 4th Thoracic Dorsal ating branches of 4th in- tercostal nerve. Posterior branch of 4th thor- acic nerve. 5th Thoracic Anterior and lateral perfor- Ventral 5th Thoracic Dorsal 6th Thoracic Ventral 6th Thoracic Dorsal ating branches of 5th inter- costal nerve. Posterior branch of 5th thor- acic nerve. Anterior and lateral perfor- ating branches of the 6th intercostal nerve. Posterior branch of 6th thor- acic nerve. Second thoracic zone, small area in dorso-mesial surface of arm. Ventral landmark, 4th sterno-chondral junc- tion. Dorsal landmark, the 3rd thoracic spine. Third thoracic zone. Ventral landmark, 4th sterno-chon- dral junction. Dorsal landmark, 4th thor- acic spine. 3rd Thoracic 4th Thoracic Fourth thoracic zone. \en- tral landmark, 5th and 6th sterno-chondral junctions, ,5th Thoracic Dorsal landmark, 6th thor- acic spine. Fifth thoracic zone. Ventral landmark, base of xyphoid cartilage. Dorsal landmark, 7th thor- acic spine. 6th Thoracic 172 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM 7 th Tlioracic Ventral 7th Thoracic Dorsal ^^th Thoracic Ventral sth Thoracic Dorsal 'Jtli Thoracic Ventral !M:ii Thoracic Dorsal 1 0th Thoracic Vi-ntral 1 0th Tlioracic' Dorsal Ni'iAi- or ni'i \ rs in w hirtj t Iun area of iiuicr\-atiuM i-oriTspolnl^ Anterior and lateral perfor- ating branches of 7th in- tercostal nerve. Posterior branch of 7th thor- acic nerve. Area .^u]lpli»■d hy dorrnatouir- an*] t^i'ucral landmarks in its ' topof^raphy Dorsal nf-rvc- root corrf's- ponding to derniatonie li'irst abdcjminal zone, ^^'n- tral landmark, tip cif xy- phoid. 7tli Thoracic Dorsal landmark, Sth and 9th tlioracic spine. lltli Th.>racir Ventral 11th Thoracic Dorsal Anterior and hrtcral perfor- ating branches of Sth in- tercostal nerve. Posterior branch of Sth tlior- acic nerve. .\nterior and lateral perfur- ating branches of ittli in- t<>rcostal nerve. Posterior branch of (Itli thor- acic nerve. .\iiterior and lateral perfor- .'iting Ijranchcs of 10th in- tercostal nerve. Posterior branch of lOth thoracic nerve. -Vnterior and lateral iiiMfor- ating branches of 11th in- tercostal nerve. Posterior branch of llth t lioracie nerve. Second abdominal zone, cor- responds to middle of epi- [ gastric zone. Sth Thoracic Dorsal landmark, 10th thor- acic spine. Tliird abdomin.a.l z Fig. 187. — Fifth lumbar dermatome. 17G FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM r „ , ■ N.-TV,: „r n,.,v,.;, t„ wl,i.-l, this area ' -''"■'' «"Pp!i«l by .l,Tmat„m.' and i Lcrmatoinc „f ,n„o.-vation ,,orrc-.p„mla I KCHfral landmark, in it., I topcRraphj- Dorsal nfTv'f root correa- ponding to d<^rmatomf oth Luinh: Ventral 5th Luo'.l.; Dorsal l.-^fc .Sacral \'entral External iiopliteal ner\-c, tliroURh the anterior tibial (tarsal branches internal and dorsal digital branches) nmsculo-cutaneons nerve. Internal i)opliteal nerve, in- ternal calcanean branches, supramalleolar branches and internal plantar branches. Posterior branch of 5th luiii- l):ir ner\-e. Small areas ventral and dor- sal to internal mallei.ilus, mesial half dorsum of foot ' including great toe. Mesitil surface of heel and ball of foot and a small strip con- necting these two along sole 5th Ijinibar of foot. In iiitergliiteal triangle. Dor- sal and ventral zones are not C(mtinuous. 1st Sacral Dorsa 1 ICxternal anil internal |)li- External surface of leg be- teal nev\'es. Dorsal internal and median bra ni' b es of iiiusculo-i'utuiicous. ex- ternal sai)lienous, external calcanean, external plantar, |>eroneal Viianch of external j saiihenous. Posteri(rr lir:ini-li of 1st sacral In interglute.al triangli nerve. -al ami vi-ntral zon not eonlinuon.s. tween internal and external axial lines below level of con- dyle of femur, lateral halt surface of dorsum and sole of foot. Toes Vjoth surfaca's. ; Dor- s are Isl Sacral Csleni^l Axial '' Line r 'Jerri?) Axia "Line --Sid Inter_n^l Axiat Line -Sis THE SPINAL CORD 177 Dermatome Nerve or nerves to which this area of innervation curreaponds Area supplied by dermatome and general landmarks in its topography Dorsal ner^'e root corres- ponding to dermatome 2nd Sacral Ventral 2nd Sacral Dorsal Gluteal branches, femoro- popliteal branches of the sciatic nerve, cutaneous peroneal branch of per- oneal and sometimes musculo-cutaneous and ex- ternal saphenous. Posterior branch of 2nd sacral Dorso-lateral surface of leg from the intermallcolar line and along the posterior sur- face of thigh between in- ternal and external axial lines up to coccygo-trochan- teric line. In intergluteal triangle. Dor- sal and ventral zones con- tinuous. 2nd Sacral s^v- Exlernal Axial Line ■Sad external Axial Line S2v ^_External Axial Line -52. d Ventral View Lateral View Dorsal View Fig. 1S9. — Second sacral dermatome InXern^l Axial Line -S3VS -S3VP Trochanfero- Coccygeji Line Exiernai A, Trapezius. 180 FOHM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Table of the Muscles S Through Dorsal Division of the Fourth Cervical Nerve. Fifth Cervical Segment Tlirouglt \'eutrat Division of Fiflli Cervical Nerve. Through Dorsal Divisiou of Fifth Cervical Nervv. Sixth Cervical Segment Througii Ventral Division of Sixth Cervical Nerve. Through Dorsal Division of Si.rth Cervical Nerve. Seventh Cervical Segment Through ]'entral Division of Seventh Cervical Nerve. Through Dorsal Division of Seventh Cervical Nerve. Eighth Cervical Segment Through Ventral Division if Eighth Cervical Nerve. Through Dorsal Divi\ion of Eiglith Cervical Nirre. First Thoracic Segment Tliroiigh \'entral Division of First IVioracic Nerve. Through Dorsal Divisiou nf First Thoracic Nivn. Secona Thoracic Segment Through Ventral Divisiou of Seviind Tlunaeic Nerve. Through Dorsul Division of Second Thorueir Nvrvr. Third and Fourth Thoracic Segments Through \'enlrnl Division of Third and Fourth Tliovocic A erres. upplied by the Several Spinal Nerves (Continued) C'lim plexus, Transverso-spinales, Splonius, Erector spinae- Longus colli, Scaleni (Diaphragm), Levator angulae, Scap- ula}, Rhomboidei, Serratus magnus, Subolavius, Supra- spinatus. Infraspinatus, Teres minor, Subscapularis, (Teres Major i, Deltoid, Triceps (Pectoralis major) Biceps, Brachialis anticus, Extensores carpi radiales. Transverso-spinales, Erector spina. Longus colli, Scaleni (Subclavius), Serratus magnus (Supras])inatus, infraspinatus, Teres minor), Subscap- ularis, Latissimus dorsi. Teres major, Deltoid, Pector- alis major, TrieejK, Biceps, Brachialis anticus, Pronator radii teres. Flexor carpi radialis, Supinator, Brachio- radialis, Extensores carpi radiales. Abductor, Opponens, and Flexor brcvis ixiUicis. Transverso-si)inales, Erector spina-. Longus ci)lli, Scalenus medius (Serratus magnus), Pector- alis major and minor, Latissimus dorsi (Teres major), Coraco-brachialis, Triceps brachii. Anconeus, Flexor sublimis digitorum (Flexor profundus digitorum, Flex- or longus poUicis, Pronator quadratus), Extensores radiales. Extensors of digits, Extensor carpi ulnans. Transverso-spinales, Erector spina. Longus cnlli, Pectoralis major and minor, Latissimus dorsi. Triceps brachii. Anconeus, Flexors of digits. Flexor carpi ulnaris. Pronator quadratus, Adductores pollicis, Interossei, Alxluctor, Flexor brevis, and Op- ponens digiti quinti. Transverso-sjjinales, Erector spina. Pectoralis major and minor. Flexors of digits. Flexor carpi ulnaris. Pronator quadratus, Intercostales, Leva- tor costa;, Serratus posticus superior, Abductor, Flexoral- l.irevis, and Opponens digiti quinti. Transverso-spinales, Erector spina. Litercdstales, Le\-atore3 costarum, Serratus posticus sup- crKir (Triangularis sterni), Transverso-spinales, Erector spina. Intercostales, Levatores costarum, superior. Triangularis sterni. Serratus posticus THE SPINAL CORD ISl Table op the Muscles Supplied by the Several Spinal Nerves {Continueil) Through Dorsal Division of Third and Fourth Thoracic Nerves. Fifth and Sixth Thoracic Segments Through Ventral Division of Fifth and Sixth Thoracic Nerves. Through Dorsal Division of Fifth and Sixth Thoracic Nerves. Seventh and Eighth Thoracic Segments Through Ve7itral Dinsion of Seventh and Eighth Thor- acic Nerves. Through Dorsal Division of Seventh and Eighth Thor- acic Nerves. Ninth, Tenth and Eleventh Thoracic Segments Through Ventral Division of Ninth, Tenth and Eleventh Thoracic Nerves. Through Dorsal Division of Ninth, Tenth and Eleventh Thoracic Nerves. Twelfth Thoracic Segment Through Ventral Division of Twelfth Thoracic Nerve. Through Dorsal Division of Twelfth Thoracic Nerve. First Lumbar Segment Through Ventral Division of First Lumhar Nerve. Through Dorsal Division of First Lumhar Nerve. Second Lumbar Segment Through Ventral Division of Second Lumhar Nerve. Through Dorsal Division of Second Lumhar Nerve. Third Lumbar Segment Through Ventral Division of ■ Third Lumhar Nerve. Through Dorsal Division of Third Lumhar Nerve. Fourth Lumbar Segment Through Ventral Division of Fourth Lumbar Nerve. Transverso-spinales, Erector spina;. Intercostales, Levatores eostarum, Triangularis sterni, Obliquas externus, Rectus abdominis. Transverso-spinales, Erector spince. Intercostales, Levatores eostarum, Subcostales, Obliquus externus, 0blic(uus internus, Transversalis abdominis, Rectus abdominis Transverso-spinales, Erector spin£e. Intercostales, Levatores eostarum, Subcostales, Sorratus posticus inferior, Obliquus externus, Obliquus internus, Transversalis abdominis. Rectus abdominis. Transverso-spinales, Erector spinie. (Quadratus lumborum), Obliquus externus, Obliquus internus, Transversalis abdominis. Rectus abdominis, Pyramidalis. Transverso-spinales, Erector spina;. Quadratus lumborum (Obliquus internus, abdominis), Cremaster. Transverso-spinales, Erector spinse. Transversalis (Quadratus lumborum), Cremaster, (Psoas parvus), lliacus, Pectineus, Adductor brevis. Gracilis, Sartorius Transverso-spinales, Erector spinse. Psoas magnus. Adductor longus, Psoas magnus, lliacus, Peetineus, Adductor longus. Ad- ductor brevis. Adductor magnus. Gracilis, Obturator externus, Sartorius, Quadriceps. JNIultifidus spinae. Erector spina:. (Psoas magnus). Adductor lirevis, Adductor magnus, Gracilis, Obturator externus. Quadriceps, Gluteus medius and minimus, Tensor fasciie latse (Gluteus 182 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM fl." C O; .2 a P - o o = S^X ^.s ! O^W Q ■u.5'Si THE SPINAL CORD 183 = ■;^tM c ^^ -3 "^ skin elow d of and the .Soo a ^ " ^ -^<2 n of the egion b ilicus an re upper part of region 5^ ^-S 0° §1 o ° .s'-s-^-a^ .2 3g M Excitnt of the the un the en extern inguin 1^ 3-S 'o ^^ p^o^^ w- 3 O- =1 ; a o t ^ c q r;s 3^-£Sa c2. £ ?^ rt m p o 1S4 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Table of the Mtkcles Supplied dy the Several Spinal Nerves (Continued) inaximus, Obturator Internus), Quadratus fenioris, Semimembranosus (Deep muscles of back of leg), Muscles of front and outer side of leg, Extensor brevis digitorum. Through Dorsal Division of Multifidus spinse. Erector spin;e. Fotirth Lumbar Ncrrc. Fifth Lumbar Segment Through Ventral Dirision of (Quadriceps) Adductor magnus. Gluteus maximus. Fifth Lumbar Nerve. medius and minimus, Tensor fascice latse (Pyriformis), Quadratus femoris. Obturator internus, Ham-strings, Muscles of leg (except gastrocnemius). Extensor brevis digitorum, Inner muscles of sole. iMultitidus spinae. Erector spina. Through Dorsal Division Fifth Lumbar Nerve. First Sacral Segment Through Ventral Division First Sacral Nerve ThrougJi Dorsal Division of First Sacral Nerve. Second Sacral Segment Through Ventral Division of Second Sacral Nerve. Through Dorsal Division of Second Sacral Nerve. Third Sacral Segment Through Ventral Division of Third Sacral Nerve. of Gluteus maximus, medius, and minimus. Tensor fasciae latae, Pyriformis, Obturator internus, Quadratus fem- oris (Adductor magnus), Ham-strings, Muscles of leg and foot. Multifidus spins. Gluteus maximus (Gluteus medius and minimus) Tensor fascia latae, Pyriformis, Obturator internus, Semi- tendinosus. Biceps (Muscles of front of leg, Peronei), Gastrocnemius, Soleus, Flexor longus hallucis (Flexor longus digitorum, Tibialis posticus). Outer muscles of sole. Perineal muscles. Multifidus spins. (Pyriformis), Biceps, long head, (Gastrocnemius, Soleus, Muscles of Sole), (Levator ani ,Coccygeus), Perineal muscles. Multifidus spins. Through Dorsal Division Third Sacral Nerve. Fourth Sacral Segment Through Ventral Division of Levator am, Coccj'gevis, Perineal muscles. Fourth Sacred Nerve. Fifth Sacral Segment Througli Ventral Division of (Coccygeus). Fifth Sacral Nerve. Names enclosed in parentheses indicate that the muscles are not always supplied from the nerve-root in question. CHAPTER XI THE SPINAL CORD THE FUNCTION OP THE WHITE MATTER IN THE CORD SEGMENT The General Arrangement and Significance of the White Matter of the Spinal Cord. The white matter or medullary substance bears a constant and characteristic relation to the gray matter in all of the segmental portions of the central nervous system. The myelinated fibers form an investment about the gray matter which, from the nature of its position, serves to limit the expansion of the gray substance. In those parts of the nervous system, on the other hand, where expansion of the cell-containing substance has been the paramount issue, the structural design departs from this more primitive arrangement. The nerve-cells take up a position outside of the medullary substance where they may multiply and expand their connec- tions without the embarrassment of a large mass of surrounding white matter. This difference in the relations of the gray to the white matter in the central nervous system affords one of the major points of differentiation between the two principal sets of organs which constitute the neuraxis. In the segmental organs, represented in the spinal cord and the brain stem, the gray matter occupies a central position and is surrounded by the white matter. In the portions of the central nervous system which have developed as additions to the segmented structures and which are, therefore, known as the su-prasegmental organs, the relation of the gray to the white matter is reversed, the cell-containing substance occupying a position outside of the medullary substance. This is true of the cortex of the cerebellum, of the tectum mesencephah and of the cerebral cortex. The central position of the gray matter in the segmental portions of the central nervous system indicates the ultimate achievement of centralized control. The nerve cells under these circumstances are most advantageously placed in relation to each other and accomplish their intercommunications in the most economical manner. The position of the white matter became subordinate in the process of centralization. The connecting fibers, in order that they might not disturb this process, have taken up positions ectal to the cell-containing mass. Such an arrangement, while in the interest of the centralization of power in the gray matter, has placed obvious restrictions upon the expan- sion of this substance. It has limited the potentiality of expansion and deprived the gray matter of still further evolutional possibilities. The important advances leading up to the development of the most efficient behavioral reactions, have not been dependent upon expansion in the segmental portions of the nervous system. Such progressive advances have come as a result of the extensive growth in the suprasegmental structures 185 186 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM already mentioned. It is evident, on the other hand, that however great this suprasegmcntal expansion may be, it would prove ineffectual unless it could exert its influence directly upon the segmented portions of the central nervovis system. In consequence, there have come into existence collections of nerve fibers which establish intimate connections between the segmental and suprasegmcntal portions of the neuraxis. These connecting fibers, however, follow the general law observed by axones in the spinal cord and brain stem in assuming positions outside of the gray matter. Groups of Fibers of the White Matter with Reference to the Connec- tions Which They Establish. Three groups of nerve fibers may be distin- guished in the white matter according to the connections which they establish. They are (1) intrasegmental fibers; (2) intersegmental fibers, and (3) suprasegmcntal fibers. Fig. 19.0. — The wlutu columns i>( the spiniil cord. Red indicates the lateral column. Bhic indicules the veritrid eohuiiu. Green indicare.s the dorsal cohmm. The position of the individual fiber in the white matter is determined by tlie length of tlie course which it must ])uvsue to make' its necessary connections. The shorter its course, the nearer to the gray matter will be the axone. Axones whose origin and destination lie within the same segment, i.e., intrasegmental fibers, will be contiguous with the gray matter. Short intersegmental fibers occupy positions imihediately peripheral to the intrasegmental fibers. The long intersegmental fibeis, as well as the supra- segmcntal fibers, occup}^ positions at a greater distance from the gray THE SPINAL CORD 187 matter. This rule, subject to minor variations, indicates the general loca- tions in cross section of the three groups of fibers entering into the white matter. The Three White Columns of the Cord. Each half of the spinal cord presents in its white matter three well-defined columns, namely, (1) the dorsal column; (2) the lateral column, and (3) the ventral column. The Dorsal Column is bounded mesially by the dorso-median septum, and laterally by the most ventral fibers in the entrance zone of the dorsal root. The Lateral Column is the portion of the white matter comprised between the entrance zone of the dorsal roots and the emergent zone of the ventral roots. The Ventral Column is all that portion of the white matter mesial to the ventral root fibers. CONSTITUENTS OF THE DORSAL WHITE COLUMN The fibers which constitute the dorsal white column are intrasegmental and intersegmental in character. The intrasegmental fibers ocawiij & }\\xia.- griseal position, that is to say, next to the gray matter, and are particu- larly close to the median fissure and the gray commissure. They take origin in the dorsal gray column and follow an ascending as well as a descenchng course. Some of them run upward, others downward, for relatively short distances, ultimately to enter the gray matter. Their function is to serve the purposes of intrasegmental association. By this means many cells of the same segment of the spinal cord are brought into active relation with each other. Intersegmental Fibers in the Dorsal White Column. The larger por- tion of the fibers of the dorsal white column are intersegmental, and two chief varieties are distinguished, the spino-bulbar intersegmental fibers and the spino-spi7ial intersegmental fibers. The Spino-Bulbar Intersegmental Fibers extend a relatively much longer distance than the spino-spinal fibers. They occupy more than four- fifths of the dorsal white column. Their fascicuh are separated from the gray matter in the region of the commissure by the interposition of the intrasegmental fibers. They are separated from the dorsal horn by the enter- ing fibers of the dorsal roots, and with a certain slight irregularity to be observed later, they extend to the dorsal periphery of the cord. Origin of the Spino-Bulbar Fibers in the Dorsal White Column. The origin of these fibers is in the dorsal root gangUon cells, whose proximal processes form the dorsal roots. These roots enter the cord in the entrant root zone in such a way that the axones sweep forward and inward toward the mesial surface of the base of the dorsal gray column. In the entrant root zone, each axone divides into a long ascending and a short descending collateral. Immediately after this division, the ascending collateral takes up a position contiguous with the fibers of the entrant zone and begins to ascend toward the brain. Upon entering the segment next above, it en- 188 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM counters the entering fibers of the dorsal root next higher in order. In conseciuence of the ascending collaterals given off by these root fibers, the collateral from the lower segment is pushed inward toward the median line. Each succt'.ssive group of entrant zone fibers, giving off its own ascend- ing collaterals, causes the fibers entering lower down to move closer toward the dorso-median septum. In this manner the fibers which come in at the level of tlie sacral segments lie close to the dorso-median septum in the cervical region, while the fibers connng in from the cervical seg- ments are nearer the entrant root zone. Tracts Formed hij the Spino-Bulbar Fibers of the Dorsal White Column. All of these fibers are heavily myelinized. Upon reaching the levels of the cervical enlargenu^nt, the long ascending intersegmental axones become subdivided into two distinct groups bj' a partition of connective tissue which extends inward from the dorso-paramedian sulcus toward the gray commissure. This partition is the dorso-paramedian septum. It divides the dorsal white column into two fasciculi or tracts, the tract of GoU or fasciculus gracilis, and the tract of Burdach or fascicidus cuneatus. The division of the dorsal white column into these two tracts, although most conspicuous in the cervical region, may also be made out in the upper thoracic segments. In the lower thoracic, lumbar and sacral segments this subdivision of the dorsal white column disappears. The significance of the two fasciculi con- stituting the spino-ljulbar portion of the dorsal white colunm is evident. The axones coming from the coccygeal, sacral, lumbar and lower thoracic spinal ganglia represent sensory areas of the lower extremities, external genitals and lower jiortion of the trunk. Successive migration of these collat- erals as thoy ascend toward the brain determines their mesial position upon reaching the level of the cervical enlargement, and hence the tract of Goll consists of sensory fibca-s from the leg, genitals and lower portion of the trunk. The fibers comprising the tract of Burdach have their origin in the spinal ganglia of the upper thoracic and cervical regions, and represent sensory areas of the upper trunk, arm and neck. They occupy a position lateral to the tract of Goll. Myelinogenetic Fields in the White Sid)staiice. It is the opinion of several authorities that the tracts of the spinal cord, during the process of develop- ment, do not convey nerve impulses until they have received their myelin sheaths. Upon this basis the theory has been constructed that the more fundamental bundles in the white matter receive their myeUn sheaths at an early period. According to Flechsig, three portions of the tract of Goll may be recognized according to the time of myelinization. These divisions are known as the myelinogenetic fields of Flechsig. The first of these fields to receive its myelin sheath is the ventral area extending forward almost to the gray commissure. A small area mesial to it is known as the mesial myelinogenetic field, and a third larger field of this kind called the dorso- median is present immediately beneath the periphery of the dorsal column. Between the dorso-median and ventral areas is the median myelinogenetic field. The dorso-median field receives its mvelin sheath near the end of the THE SPINAL CORD 189 ^. ■*.■ Ik ^^X;i 2. "inp-^ ^ilz 3. •%^^ a. /; ■' ■ .■ d >■■'■ ''^'-;^'^-\ ' 0/ — 4-'*'' Fig. 196. — Diagrams showing the myelinogenetic fields of the spinal cord at the different periods of fetal life. (TrepinsJd.) 1. Lumbar cord at the fifth month. 2. Cervical cord at the fifth nioiitli. 3. Lumbar cord at five and a half months. 4. Cervical cord at five and a half months. 5. Lumbar cord at the sei.-enth month. G. Cervical cord at the seventh month. o. — Dorso-median root zone; b — dorso-lateral root zone; c — anterior root zone; d — median zone. 190 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM seventh fetal month, and myehnization is nearly complete in the ventral field at the end of the fifth month. The mesial field completes its myeliniza- Dorsal Tract of Burdach Dorsal Root Dorsal Root GanQl ion Dorsal Tract of Goll Dorsal Tract pf Burd- ach Cervical SeQiriert nt Spinal Cord Dorsal Root- Dorsal Root GariQlioTi Caudal Level of Medulla Thoracic _ SeQTnent Dorsal RootGamQiionTT of Spmal Cord Dorsal Dorsal ^o^WA \ / Wx^'?^ of Dorsal Root, '' ^s^L.,,^SeQment DorsalTract of Goll— ]_ of Spmal Coi'd •Dorsal ,Grav .ColuTTin -Ventral , Gray Colurin Lower Lumbar SeQmerit iOmaesthetic JSensor/Area of Corlex Fig. 197.~The dorsal tracts of Goll and Burdach passing thrcmgli the spinal cord and repre- senting the spinal divi- sion of the spino-tliala- mo-cortical pathway. The tracts serve for the conduction of discrimi- native somesthetic im- putses from the skin, muscles, jomts and bones. tion during the fifth month and the median field is completely myelinized by the end of five and one half months of fetal life. Trepinski identifies THE SPINAL CORD 191 four fetal fields in tiie dorsal column and has called attention to the parallel- ism which seems to exist between the physiological myelinization during embryonic life and the pathological degeneration of the dorsal column which occurs in tabes dorsalis. Flechsig also recognized myelinogenetic areas in the tract of Burdach in which he was able to distinguish a ventral, a middle and a dorsal field, each of which received its myelin sheath at a different period of development. As a whole, the tract of Burdach undergoes myelini- zation at a relatively late period, i.e., at the end of the seventh fetal month or near the beginning of the eighth month. It is remarkable in certain cases of tabes dorsalis to note the manner in which the degeneration of the dorsal column fibers in the tracts of Goll and Burdach follow the order of myeliniza- tion observed during development. The fibers first myelinized are first to degenerate, while those which receive their myelin sheath later show a degenerative change at a subsequent period in the disease. Course of the Tracts of Goll and Burdach. The tract of Goll continues its ascent from the lower segments of the cord to the medulla oblongata; the tract of Burdach, beginning in the upper thoracic segments, passes upward, receives an increment as it ascends, and finally ends in the medulla. Both of these tracts convey afferent impulses toward the brain. Were it not for the fact that they receive a relay in the medulla oblongata, the impulses which they conduct would fall short of their goal. In the medulla, each of these tracts comes into synaptic relation with a special nucleufj which serves as a relay station on the way toward the brain. The tract of Goll ends in the nucleus gracilis, while the tract of Burdach has its termination in the nucleus cuneatus. B.oth of these nuclei will be described in the discussion of the medulla oblongata. Functions of the Tracts of Goll and Burdach. Although it is clear that the tracts of Goll and Burdach convey afferent impulses, a more precise under- standing of their type is necessary. It is to be borne in mind that the fibers of these tracts remain ipsilateral throughout their entire course in the spinal cord. Whatever impulses they convey must, therefore, come from the corres- ponding half of the body. It has been shown by cUnical observation and by pathological control of carefuhy studied cases that the fibers ascending in the tracts of Goll and Burdach conduct special types of sensibiHty. Im- portant among these sensory impulses are those concerned in the muscle and joint sensibihty, bathesthesic sensibility. Even this is scarcely enough to distinguish the types of sensory impulses which pass by way of the dorsal column. Experience teaches that only a certain quahty of muscle and joint sensibihty ascends in this position toward the brain, i.e., that quality of sensory impulses which has to do with muscle and joint discrimination. Muscular activity without this discriminative direction becomes irregular Ind incoordinate, while the movements entering into motor action are either excessive or inadequate. Such is the case, for example, in tabes dorsaUs, in which disease the patient presents an actual locomotor ataxia. In per- forming skilled acts with the upper extremities he often manifests an inexac- titude in the execution of his motor activities. 192 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Another type of diseriminative sensibility, tactile discrimination, also makes its way upward in the dorsal column. By means of this sense quality the individual is able to localize the point of contact upon the skin with a certain degree of exactness. His accuracy depends upon the area of skin stimulated. Localization on the balls of the fingers, upon the surface of the hands and on the tips of the toes is accurate within the limits of about one- half centimeter. This distance becomes greatly increased upon other surfaces of the body in which discrimination is of less value to the individual. By means of tactile discrimination, it is possible to recognize the differ- ence in distance between two points coming in contact with the skin. This is tested by a compass or pair of dividers. The distances between the two points constitute the radii of circles which are known as the circles of Weber. In parts of the skin most emploj^ed in the critical activities of sensibility, the circles of Weber are relatively small, the radii varying from one-quarter to one-half a centimeter. In other parts of the body where such discrimination is less useful, the circles of Weber are large, their radii varying from one to four centimeters. Pressure Sensibility (Piezesthesia). Impulses necessary to pressure dis- crimination are also conveyed toward the brain in the columns of GoU and Burdach. Vibratory Sensibility (Pallesthesia) . This also is proliably a discriminative type of scnsibihty conducted by the columns of Goll and Burdach. In general, the spino-bulbar fibers in the dorsal white column convey impulses of all forms of discriminative somesthetic sensibility. The Spino-Spinal Intersegmental Fibers. These fibers are of two varieties, those which ascend, and those which form well-marked bundles of descending axones. Descending intersegmental fibers appear in the dorsal column in relatively small numbers; they occupy difi^erent positions at different levels of the cord. In the sacral region, these fibers are collected in a small strand at the dorso-mesial angle of the column and constitute the triangular bundle of Philippe-Gombault. In the lumbar region, they appear as a semi-oval area adjacent to the dorso-median septum. This is the oval bundle of Flechsig. In the cervical and thoracic regions of the cord, the descending spino- spinal fibers are more scattered and do not form discrete bundles as in the lower segments. One bundle of this variety is situated contiguous to the gray matter at the junction of the dorsal horn and the commissure. This is the cornu-commissural bundle of Bruce. Another small descending fasciculus in the dorsal white column appears at about the middle of this region in the form of a comma-shaped collection of fibers. It is most prominent in the thoracic portion of the cord and is known as the comma tract of Schultze. It is beheved that its fibers either originate in cells of the gray matter in the dorsal column or else are descend- ing collaterals from the axones of the dorsal roots. THE SPINAL CORU 193 All the descending intersegmental spino-spinal tracts, with the possible exception of the fibers forming the comma tract of Schultze, take origin in cells situated in the gray matter. They pass downward from one to three seg- ments of the cord, and some extend even a greater distance; many of these fibers turn into the gray matter in order to establish intersegmental associa- tions between cells of their own segment and other cells in segments occupy- ing more caudal positions. The Tract of Lissauer. Most of the fibers of the dorsrd column are heav- ily myelinized and are derived either from the mesial entrance zone of the ,-H^^ ■■^i ^i^'^N -^*^. v^ -jv^ ( ?^:>^ \ "1 ' '' / •J^V.-^ -.w. Fig. 200. — ,Spino-spiiial mtersegmental libi/r.-s. Blue indicates the location of the fomnia tract of Schultze. To facilitate description, the lateral white column may Ije divided into the following zones: (1) the juxtagriseal zone; (2) the circumferential zone, and (3) the inter- mediate zone. The juxtagriseal zone is an area of white matter of con.siderable thickness immediately in contact with the gray matter. The circumferential zone begins at the tract of Lissauer and extends along the periphery of the cord as far forward as the mesial fibers of the ventral roots. The intermediate zone constitutes the area intervening between these two zones, and is larger than either of them. 196 FORM AXD FUNCTIONS OF THK CENTRAL NERVOUS SYSTEM The Juxtagriseal Zone is inailij up <'xclusivcly of intorseumental and intrascsiacntal fillers. j\Iany of thei^c filxTs are both ascending and de- scending, and many of tlieni eonie from tiact cells situated upon the same side in tin: i2;ray matter, tha(. is, tautamcnc cells. Others arise from the tract rcHs on tin' nppositi' side, tlia.t is, h(>t.('romei-ic cells, "riicse spino- P\'rLiiiuiial Tract rj("ir,~:i) Sj,iiifi-Prrrl".c]l:ir Tn.rt Knliru-jl.iiKil Trfirt . Dorsal Si.iiin-tliLilliriiir Tnn't ^^■Illr;ll ■'^iiinip-ei-n Tract \'rTitrFil SlHliM-lliLilalnic Tra't __ Fig. 2in.--']'lie tliro.' z.mr-s nf tlw I,-ili'r:il wlntr r..liiiim. Upi| indicatr-s tlic firriuiitcrential zone; ijlue imlicaLcs the iutci-iarilialc znuo; giuiai iiirUcatos the juxtasviseal zciiie. spinal ascendiii,!; and desceiidin-- jifirrs always bear the same intimate relation to the gray matter of the cord, sendiirc; their axones up or down for a distance of several segments and serving to connect the nerve-cells in the chffei-ent levels ^\■ith one aiiotlier. In the upper cervical segments where the formuliii rciicidaris is pronounced, many intersegmental fibers serve to connect the icticula.r formation (jf the spinal cord with that of the medulla oblongata. The Circumferential Zone consists of two suprasegmental tracts and two intersegmenial tracts. The suprascgmental fasciculi are both aacencUng tracts, namely: ( l) the dor:ml spino-ccrchrllitr tniH, and (2j the rcntral t:pino- cerehdlur Irart. J^^oth of the intersegmental tracts connect the medulla oblongata wil-h t,he spinal cord. One of these is (3) the Dcitero-spinal tract, whii;'li constitutes a descemling oi- bull)o-spinal connection, while the other THE SPINAL CORD 197 is a descending tract, (4-), the fasciviibis of H el w eg, which constitutes the olivo-spinal tract. The Dorsal Splmo-Cerebellar Tract or Direct Cerebellar Tract OF Flechsig lies lateral to the pyramidal tract along the outer surface of the cord, wliere it occupies a somewhat narrow area. It extends forward Caudal Level ^ of Medulla ((>' Dorsal Root GaTiQlion Dorsal Spino Cerebellar^ Trad Dorsal Root GanQlion Dor5al Spinal Root Dorsal Spino Cerebellar Trac (TautoTTieric CereDeiium TermTL'icn cf Ventral Spino- cerebel iar Tract orav fConiTnissure ^Cervical ,^;';''SeQment of #5pmal Cord Ventral Spino- cerebellar Tract jiCTautomeric and fiHeteroineric) i ; Thoracic SeQirent ^of Spinal Cord oiucrn of Clarke Partial Decussation of Ventral Spino- cerebellar Tract Thoracic Seoment of Spinal Cord Lower Lumbar SeQTTient of 5pinal Cord . 201'.— Tlio \'Oiiti:il ami liors.'il spino-crrebellur tracts, passing through 1 he spinal cord and rcp- r('s<'nting the spinal di- \-ision of the spino- rerebellar jiathway. These tracts ser\fc lor the conduction of im- pulses from the somatic muscles to the cere- helium. T!ie tracts form (he tUTerent arms of the reflex arcs wliose center is in the eerebelkun. They are part of the mechanism active in synergic control of the muscles. from the tract of Lissauer to a point midway hetwecn tlie tlorsal and ventral root fibers. In the lower thoracic portions of the cord where the crossed pyramidal tract is coming closer to the periphery, several bundles of pyra- niidal fibers interpose themselves between 1h<' dorsal extiTanity of the tract of Flechsig and the dorsal horn. 19S FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Tlio dorsal spind-ccrchellar tract Ijc^ins to appear in tlio twelfth thoracic scfrnieiit in man. AlioA'e this level it is present in all segments of the cord. It passes into the medulla ohlon^ata and eventually enters the inferior cere- bellar peduncle, by means of which it r(!aches the vermis of tlie cerebellum. On'fiiii (if thr Dorxiil Spino-Ccrchdiar Tract. This tract takes origin in the cells of Clarke's column, the axones of wliich travcn-we the gray matter of the same side and, entering the white matter, finally take up an ascending position as the direct cerebellar tract. Destination and Course of tlic Dorso-Spino-CerebeUar Tract. The tract holds this circumferential position thi-oughout its course in the cord. In the medulla oblongata it becomes one of the constituents of the inferior cere- bellar peduncle. It has its destination in the vermis or middle lobe of the cerebellum. Functions of the Dorsal Spirio-Cerebellar Tract. The dorsal spino- cerebellar tract serves as an ipsilateral connection between the muscles of one side of the body and the cei'ebcllum of the same side. Its function is to convey to the cereliellum impulses from the nuiscles, in order to furnish that organ with the stunulation adec(uate to the maintenance of coordina- tion. When this connection is defective, the cereljcllum is no huiger properly informed as to the muscular status and it is consequently in no condition to transmit the proper impulses to the muscles which determine coordinated action. The \'entral Spino-Cerebellar Tract or the Cerebellar Tract of Cover. This tract lies in the circumferential zone immediately ventral to the dorsal spino-cerebellar trai't. It is smalk'r tlian Flechsig's tract and less compact. It extends along the periphery of the cord as far as the ventral root fibers. It makes its first appearance in the first and second lumbar segments, being somewhat longer than the tract of Flechsig. Origin of the Ventral Spino-Ccrrlicllar Tract. Some of its fibers may arise in the cells of Clarke's eolunui,andnianj' also take origin in the body of the gray matter. It is possiljle that some of its axones arise from cells upon the opposite side. Dc-iti nation oud Course spinal cor- to entei' the opposite eerebellar hemisphere. Intermingle(l with the ascending cerebellar fibers in Cower's tract are axis-cylinders of smaller diaiiieter which :iscend to the midbrain and end in tlie ti'ctuni mesencepliali. These fibers constituli- the spino-tectal tract. The fuiK'tion of tlie ventral spiiio-cereljcllar tract is, in general, similar lo tliat of Flei-hsig's tract. The Lateral Deitero-Spinal Tract. The most ventral of the fibers in the circumferential zone of the lateral white column constitute the lateral THE SPINAL CORD 199 Caiidal Level of Medulla Ventral uncrossed Oeitero-spmal TtqcX Cervical Seomerit of spinal Cord Dorsal uncrossed Deitero-spinal Tract l/enti'al Gray ColiiTTin CeV Deitero- spinal Synapsis firal CornmonPdiri'A^ ThOVdClC Segment of Spinal Cord Ventral Crossed Deitero-spinal Tract Ventral Gray Column Cell -Thoracic SeQinent oft he Spinal Cord rinal Common Pathway Lower Liimbar egmentofthe Spinal Cord Fk;. 203. — Tlie Deitero-spinal tracts passing through tlie spinal f cord and repre- senting the spinal divi- sion of the "v estibulo- Deitero-spinal path way. These tracts serve to con- duct the im- pulses neces- sary to equi- 1 ibrator y control which ari.se in the semi - circular canals , the utricle and saccule. 200 FORM AND FTXCTIONS OF THE CENTRAL NERA'OUS SYSTEM Dcitero-spiiial tract. Tliis l)undl(' of fihcrs in cross section extends from the ventral extremity of the olivo-spinal fasciculus along the periphery of the cord as far forward as the most mesial of the ventral root fibers. Origin of the Lateral Deitero-Sijinal Traet. This tract arises in Deiter's nucleus in the medulla oblongata and descends through the entire length of the cord as far as the lower sacral segments. The lateral Deitero-spinal tract rcMnains ipsilateral throughout its coarse and has its destination in the ventral column cells in all of the segments through which it passes. Funetion of the Deitero-Spinal Tract. Its function is to bring the somatic muscles under the direct control of the semicircirlar canals in the interests of maintaining equilibriimi. It is thus the direct pathwa>' which serves to distribute the impulses of vestibulo-e(iuilil.)ratory control to the motor cells of the ventral gray column. The Spino-Olivary (OLn'O-SpiXAL) Tract or Tract of Helweg. This tract is a small, triangular bundle of fillers lying ventral to Gower's tract in the circumferential zone. Its fibers are descending and connect the upper levels of the spinal cord with the inferior olivary body of the medulla. The origin and destination of these fil)ers are not definitely known and in consequence the function of Helwcg's bundle is not understood. According to some authoriiics, the lateral Deitero-spinal tract is com- prised in the composite arit:riiir mar'jinnl fity.cicnlus of Loeneitthal. Other authorities, however, maintain that the fasciculus of Loewenthal consists exclusively of descending axones from cells situated in the cerebellum. In the spinal cord the fibers of this fasciculus lie along the vcnitral margin of the circumferential zoni^ and in jiaii overlap the tract of < Jower. Whether all of the fibers in the antcrioi' marginal fasciculus iiass without interruption from the cere.bellum to 1 lie coi'd. or whether they are all interrupted in Deiter's nucleus, is still a matter of doubt. There is some evidence to show thai the fasciculus of Loewenthal contains at least two constituent tracts: (ll a Lirge Deitero-spinal tract establishing an uncrossed conned ion lietween Deit(>r's nucleus and the ven- tral gray column of the coi-d. and (2) a. lesser bumlle probabl>' containing fibers from the cerebelhini of the same side, i.e.. an iiisilateral cerebello- spinal tract . The Intermediate Zone. Tins zoik? is composed of three principal tiacts, two of which are suiirasegmental: (1) the peiUio-spinal or lateral pyrajn.idal traet, (2) the spino-thalatnii- Inicf, in addition to wliicli there is one intersegmental tract, (.3) the rvhro-Kjiinnl tract. Tilt; Latkral Pyramidal Thai t. ( Pallio-Spixal Tract). The lateral or crossed pyramidal 1ract is a large fasciculus of fibers lying m the ilorsal part of the lateral column. It extends to the lowest sacral segments of the cord. In the ceivic.al and (liora.cic segments it is separa.ted from the surface of tin' cc.ird liy tlie direct cereljcllar tract. In the lumbar segments, the lattci- tract is no longer jji-esent, and for this reason the crossed pyra- midal fibers come to the surface. This fact sei'ves ;is one of the distinguish- ing features of the lumbar and sacral cross sections of the cord. The lateral THE SPINAL CORD 201 Decussated PyraTTiidal Hbers PvraTnidal Decussation Caudal Level of the Medulla Cervical SeameTit of the Spinal Cord Undecussated .^ PYramidal ' ribers Synapsis Betwee PyraTTiidal fiber and Ventral Gray Column Ce" rmal Common Pat n way Crossed Pyramidal Tract Tinal Common Pdtnway Thoracic Seoment of the Spinal Cord Direct Pyramid- al Tract irect Pyra- midal Tract riber Decuss- ating mSGQ- ment of Destin- ation vThoracic Soq- entofthe Spinal Cord Lumbar Segment of the 'Spinal Cord . 204.— The pyra- midal tract pa.=!,s- iiig through the spinal cord. This tract serves for tlie conduction of impulses from the giant pyramidal cells of the pre- central cortex to the ventral gray column cells in tlie interest of \-olitional control over the somatic musculature. 202 FORM AND FrXrTIONS OF THE CENTRAL NERVOrS SYSTEM pvrainidal ti'uct may he traced as far cranially as the medulla oblongata, where it undergoes a complete decussation with the corresponding fibers from the opposite side. It then entei'S into the formation of a large pro- tulx'rancc upon the ventral surface of the medulla, the pyramid. This tract is constant in all of the higher mammals and man. It is composed of seventy- five to ninety per cent of all of the pallio-spinal fibers which arise in the motor area of the cerebral cortc!X. In fifteen per cent of the cases in man all the fibers arising from the motor cortex form a complete crossing in the pyramidal decussation, and no ventral or direct pyrainuUd trad is present. In many mammals all of the pyramidal fillers cross fi'om one side to the othei' in the medulla oblongata, and the lateral pyramidal tract thus represents the total pallio-spinal connection. This is the case in the lower monkeys, although a small percentage of the pyramidal fibers do not descend in the lateral pyra- midal tiact in the anthroj^oid apes. In some nnxmmals, especially the mouse, rat, guinea-]Mg, sfpiirrel, shee]:i and kangaroo, the entire pyramidal tract runs downward in the dorsal white column; but in the majority of mammals, inclu(Ung the ralil)it, cat, dog and monkey, this tract lies in the latei'al column. Origin af the Pyramidal Tract. The filjrrs of the pyramidal tract take their origin in the ]-!etz cells of tlie motor (-ortex in the Rolandic area of the brain. The>- descend through the corona lailiata, the internal capsule, the cereljral pe(luncle, the ]ions, and the uppermost portions of the medulla upon the side in which tliey arise. Course, Destination and Function of tin' Pyramidal Tract. In the medulla oblongata the pyramidal fillers undergo a jiartial decussation, in which the majoiit}- of them ci-oss from one side to the otln-r. The crossing fil)ers then become collected and descend into the spinal cord as the lateral pyramidal tract. The axones of the ]iyramidal tract end either bj' direct end-arboriza- tion about the dendrites of the venti'al column cells, or establish this connec- tion through the interposition of a nuclear collection of cells known as the lateral basal nucleus in the gray matter of the spinal cord. The function of the jiyramidal tract is to ]irovide the ventral gray column cells with voli- tional ami inhibitory control. The Spixo-Th.'VLamic Tr.\ct. By melius of this collection of fibers, a supra-segmcntal connection is established. The tract provides conduction toward the brain for certain impulses wliich come in by way of the en- trant zone into the spinal cord. Origin of the Spino-TJailmnic Tract. The fifiers constituting the spino- thalamic tiact take origin m cells situated in the substantia gelatinosa in nearly all levels of the spinal cord. It is also probable that the fibers take oi'igin in si-attered groups situat.i'd diffusely in the dorsal gray column. Course of the Spinej-thalamic Tract. Arising from these nerve cells, the axones ascend in the gray matter through several segments, making an oblique coui-se in the direction of the gray commissure in which thi^y finally cross to the opposite side. This i)ortion of their ascent toward the brain THE SPINAL CORD 203 Dorsal Root GanQlion Cell Dorsal Gray/ Column Cellf^ Dorsal Root Dorsal Root Ganglion Gel Caudal Level otthe Medulla Cervical Segment of theSpinalCbrd 'Spino-thalamic Tract h oracle Segment ot the Spinal Cord Fig Thoracic SeQirient ofthe Spinal Cord Dorsal Gray Column Cell Decussating fibers Lumbar . Segment of theSpinal Cord 2(l5.^The spino-thalamic tract passing through the spinal cord and repre- senting the spinal divi- sion of the spino - thala- nio - cortical pathway. This tract serves to conduct im- pulses of affec- tive sensi- bility, pain, d iscomfort and tempera- ture. It is call- ed the spinal fillet because it undergoes complete de- cussation in the spinal cord. 204 FORM AND l-niNCTIONS OF THE CENTRAL NERVOUS SYSTEM presents u u;i!n(Tal (>l)lii|ui( \' Uotn liclow ujjward am] inward and Ijrings each axone into the opposite inteimediatc zone of the lateral white column where it turns upward to become associate' lie veiili-al to tlie central canal or, where this is occluded, ■\'entral to the remnant of that embryonic cavity. Relations of the Spino-Tludamic Tract. Tlie colli'cled gi-iiup of fibers wlrich constitutes the sijimi-thalamie tract hes in tlie intermediate zone ol' the white matter ro-spinal tract. Destination and Connection of the Spinu-Tlialamic Tract. The spino- thalamic tract connects the spinal cord with the optic thalamus. This, how- ever, is a crossed connection due to the fact that the fibers entering into this tract cross in the cord from the side oi their origin into the opposite white column. The rnon^ e.xact, destination of the tiljcrs m the optic thalamus will be considered in Chapter XXIII. [•'unction of the Sj)ui(i-Thida)nic Tract. This fasciculus serves to con- duct impulses of pain and tianperatnre sensibility. It will be seen that the fibers composing this trai't are dislitict from those which have to do with the critical cpialities of sensiliility, which occupy positions m the dorsal white column of the cord. l"or this reason it is jiossible that a lesion may so affect th(! nerve fibers in the cord as to cause a. loss of i)ain and temperature sensibility without mvoh'iiig ei-itical sensiljilily. It is believed (hat the spino-thalamie tra(.'t serves for the conduction of all varieties of pain, Ixith dee]! and superficial, and thus provides part of the pa,thway lor the hml clciianit of s(jmatie sensibility. Clinical evidence seems lo indicate that stimuli necessary for i-ritieal as well as for aft'ective tempera- ture s<'nsibilit}' make their way to the lirain in the spino-thalamic tract. It is i)ossible, howiv'i'r, that these fillers nia\' be wholly for thosi^ temperature stimuli which tr.ansci.'iid the normal limits ol' temi)ei,ature discrimination, ami, [.leeoming painful, serve in the capacity of [uoducing reflexes which are part of the defence mechanism of the bod\'. ,A small ventral subdivision of tllis fasciculus, the rmlral spi iin-ttialaiinc tract, is b(Tie\-eil to conduct non- critieal ("»r aftV-'cti\'e (aclilf impulses. the spinal cokd 20/1 The Rubro-Spixal Tract or Fasciculus ,\berraxs of AJoxakow. This tract is often referred to as the extrapyramidal viotur fusciculu--^. Origin of the Rubro-SpinnI Tract. As its name iuii)hes, this ti'act is a Ijundlt' of fillers which descends into the spinal cord. Tlie area from whicli its axones take origin is located in the midbrain, in a nucleus of consider- able size, the nucleus ruber or red nucleus. The cells in tliis nucleus are undoubtedly of the motor t3'pe, a fact of consideral)le sittnificance concern- ing the function of the nucleus itself. Course of the Rubru-Spirial Tract. Leaving the cells of the ri'd nucleus, the axones immediately cross from one side to the other, thus forming a decussation which takes place in the midbr;an, the ventral teginentn.l dccus- sation ofForel. Aftei' ci'ossing, the hbers become collected and occupy a lateral position in the tegmentum of the brain-stem. These fibers finally enter the lateral white column in its intermediate zone and in this position descend the entire length of the cord. Relations af the Rubro-Spinal Tract. This tract occupic-- a pesition ventral to the crossed pyramidal tracts in the laliTal white column. It is situ- ated dorsal to the spino-thalamic tract, mesial to ( iowcr's tract in the cer- vical, thoracic and upper lumbar segments, while in the lower lumbar ant! sacral segments, it lies in the circumferential zone. The characteristic rela- tion of the rubro-sjiinal tract to the crossed pyriunidal and spino-thalamic tracts is one of the most constant features in the white matter of the spinal cord. In the medulla oblongata, however, this relation is somewhat changed, due to the fact that the pyramidal fibers take up another position and part company with the other two associated fasciculi. The rul^ro-spinal and spino- thalamic tracts, on the other hand, maintain tlieir constant relation, not only in the spinal cord, but also throughout the brain-stem up to the origin of the lubro-spinal bundle. Destination and Connections of the Rubro-.' a juxtagriseal position, ser^'e the purposes of bringing about intersegmental association between one cord segment and another, of associating a m.imber of I'ljrd segments, or of luinging the upper portion of the spinal cord into ivlatinn with the segments of the medulla oblongata. 2. Intersegmental connections exist between Deiter's nucleus in the medulla oblongata and the final common pathway in the spinal cord that is to say, the motor cells in the ventral gray column. Tliis intro- duces the element of vestibulo-equilibratory control over the nuiscles ef the body. 3. Afferent suprasegmental connections between the spinal conl and the cerebellum exist for the purpose of apprising that organ of the muscular THE SPINAL CORD 209 status in the interests of synergic foutrol. This is accomplished througli the tracts of Gower and Flechsig. 4. An afferent suprasegraental connection from the spinal cord to the optic tlialamus serves the purpose of conveying the sensory stimuh con- cerned in affective sensibility, that is, pain of all varieties and probabl}' temperature stimuli which transcend critical limits. 5. A connection between the midbrain roof and the cord is also to be considered in the tecto-si)inal tract. This may be in the interests (jf con- tributing a visuo-biachial conti'ol for movements of the arm and head to protect the eye in the event of sudden extreme illumination. 6. An efferent supraseginental connection from the cerebellum In' way of tire rubro-spinal tract in the interest of synergic control. Tliere is anotlier possiljle efferent cercbello-spinal connection in the triict of Loewenthal. This undoubtedl}' has the same significance as tfie rubro- spinal tract. 7. An efferent suprasegmental connection from the corpus striatum by way of the rul^ro-spinal. tract serves in the interest of automatic associative control of the muscles. 8. An efferent suprasegmental connection from the motor cortex in the endbrain serves in the interest of volitional control of the muscles. Only one of tlie eight prmcijial connections in the lateral white column bears a direct relation to sensibility, the spino-ihalamic trad. Five of the remaining tracts are related to motor regulation of the final common path- way. The lateral white column, therefore, is preponderatingly motor, being in marked contrast to the dorsal white column, which in man is essentially sensory. THE eOXSTITUEXTS OF THE VENTRAL AVHITE COLUJIX This column may ha subdivided into (f ) a juxtagriseal zone, (2) a mar- ginal zone, and (3) an intermediate zone. The line of demarcation between these areas is not sharp and there is some overlapping as in the case of the other columns. The juxtafjnseul zoiw consists of intersegmental association filjers. The marginnl zone or the facicahis viaeejinnUs anlenor «f Meirie com- prises three principal fascicuh: (f) the fasciculus longitudmalis posterior; (2) the crossed ventral Deitero-spinal tract, and fS) the uncrossed Deitero- spinal tract. The Fasctcu-lus Longitudinalis Posterior. This tract takes origin in the tectum of the midbrain, probably m the nucleus of Darksche- ivitsch or the interstitial nucleus of Cajal in the mid-lwain. Some of its fibers also arise in Deiter's nucleus. This fasciculus descends through- out the entire length of the cord in the marginal zone. It estabhshes connections between the midbrain and Deiter's nucleus on the one hand, and the motor cells m the A-entral gray column of the cord on the other. It thus li 210 FORM AND FI'XCTKIXS OF THE (JENTRAL NERVOUS SYSTEM rascicLiius LoriQitLidinalis Posterior Caudal Level of Medulla f, Tecto-spinal Tract Hnal Common Pathway Cervical Segment of Spinal Cord Ventral Gray Column Cel' Thoracic Segment of Spinal Cord Tecto-spmal Tract Tmal Common Pathway Thoracic Segment of Spinal Cord Fi. Lumbar SeQmeni of Spinal Cord na; ComnionPathv^s-v Ti'idl C-CTmnori PatHvoy . 20S.— The fascieulu.s longitudinalis posterinr and the tcctu-spimil tract in the spinal conl. Tliese serve fur the conduction of impulses from the tectum of the midbrain and the inter- stitial nucleus of Cajal to the ventral gray column cells of the cer- vical segments of the spinal cord and between the nuclei of the oculo- motor mechanism. They serve as a part of the protective nir- chanism against exces- sive light impulses and other possible injuries. The fascicuhis lon.gi- tudinalis posterior con- tains both ascending and descending fibers. THE SPINAL CORD 211 introduces into the final common patliway elements which are concerned in the regulation of somatic motion. The Deitero-spinal connection is in the interests of vestibulo-eciuilibratory control, while the significance of the mesencephalo-spinal connection is not entirely clear. The interntediate zone contains the uncrossed pyramidal tract or the fasciculus of Tiirck. The Uncrossed Pyramidal Tract or the Faclculus of Tiirck. This bundle is complementary to the crossed pyramidal tract and is sepa- rated from it, due to the fact tliat the pyramidal decussation is a partial one. The crossing involves the majority of the fibers which establish a connection between the motor cortex and the final common pathway-. A certain portion of the axones, however, do not undergo decussation in the medulla and descend in their ventral position through the cord. Origin of the Uncrossed Pyramidal Tract. The fibers of this tract arise in the Betz cells in the motor ai'ea in the endbrain. Course of the Uncrossed Pyramidal Tract. These fibers, in association with the other pyramidal tract fibers, descend through the internal capsule into the cerebral peduncle, through the pons into the medulla oblongata. At this point they part companj' with the crossed pyiamidal fibers. The; fasciculus of Tiirck descends into and enters the cord in the ventral white column and continues in this position throughout its course. It de(;reases in size in the thoracic segments of the spinal cord and disappears in th(; lower lumbar segments. Destination and. Connections of the Uncrossed Pyramidal Tract. Bj- means of the uncrossed pyramidal tract, the pallium of the endbiain in its motor area is brought into connection with the ventral gray column of the opposite side. This contralateral connection is determined by the fact that the fibers of the uncrossed pyramidal tract cross from the side in which they are descending to the opposite side through the ventral white commissure of the spinal coj'd. This brmgs the end branches of the axones into relation with the motor cells of the ventral gray column. The unci'ossed pyramidal tract is analogous to the crossed pyramidal tract. It conveys the same type of impulses and furnishes a contralateral connection Ijetween the motor area in the brain and the motor cells in the spinal cord. Summary of the Functions of the Ventral White Column of the Cord. The ventral white column of the cord sei'ves many of the same purposes of conduction as the lateral white column. It is prcpon.leratingly motor m character. Most of its tracts are of the descending type, althougli there ls some question as to the actual constituents m the fasciculus niarginahs anterior of Marie. 1. The juxtagriseal fibers afford connections Ijctwcen onesegnient and the next or l>etwcen several segments. 2. An intersegmental connection is provided by atractaiising m Deitei-'s nucleus and descending into the spinal cord. It s(a-ves to bring the nmscles under the influence of the semicircular canals in the interest of vestibulo- e(iuilibrat<.iry control. 212 FORM AXl) FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM 3. A supr;i,S(',i;;inent,:il councction bctwoi^ii the motor cortex of the end- brain and th(^ A'cntral gray column colls of tlie opposite side is provided by the fasciculus of Tiirck in the interest of volitional nrotor conti'ol. 4. A suprasegmental connection is provided l>y the tecto-spinal tract which associates certain iiortioDs of the rnidlirain with the spinal cord. This ]5robably is a priun(i\'i: suprasegniental connection and has greater significance in I he loA\'('r \'ertel)rntes than in man. CHAPTER XII THE SPINAL CORD ITS PRINCIPAL SYNDROMES It is now possible to arrive at a conception of the spinal cord as a whole, to visualize the offi.ce of this organ in regulating the activities of the body, and to appreciate the significance of the various syniptoui-comjilexes which may be produced in consequence of pathological ])rocesses affecting its several parts. Functions of the Spinal Cord in General. The spinal cord is the im- mediate administrative anil regulating organ controlling tlie somatic activities of the arms, legs, trunk and neck. It also contributes to the regulation of the visceral activities. Its chief function is the dispatch of activating impulses to the executive organs of (he body — the muscular tissue and glands, in order that these structures may cooperate in an adequate expression of the animal's life. Without the s])inal cord, all such expi'cssions of life in the extremities, neck and trunk would cease. The spinal cord brings influences to bear upon the executive organs from many parts of the nervous system. Eacli of these ])arts contributes a some- what different yet essential influence. It is the especial office of the si)inal cord to receive and blend tlu'se influences and finally to transmit them in such combinations as may be necessarj- for harmonious action. The spinal cord furnishes the final common pathway for all t lie somatic motor impulses of the body with the exception of the head. This common pathway may itsell' suiter impairment or destruction as a result of disease or injury. In such case, none of the somatic motor impulses is delivered to its respective effectors. The final common pathway may be cut off from one or more of the sources from which it receives important regulating influence. In such a case, somatic motor activities \\-ould manifest one or more pathological defects. The Isomeric and Allomeric Functions of the Cord Segment. In addition to furnislung tlie final common pathway for all somatic motor activities, the spinal cord acts as a series of governing segments controlling the several segments of the body. Each body segment may be likened to a principality or state whose government is vested m a centrally placed capital, the spinal cord segment. Allliough the segmental character of the body may be recognized in many invertebrates, its distinctness m the vei-te- brates has been largely obscured by segmental fusions in response to tlie need of more intimate cooperation of the body segments in the purposes of fife. In this way, the independence of segmental individuality has seemingly been sacrificed in the interests of greater efficiency through mutual segmental 213 214 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM I'oopciatioii, yet tlic fundainoiital segmentation of the body and spinal eord, to whatever extent obseured, still remains a potent fact. Upon its reeogniticiii depends a proper understanding of the diseases of the spinal i-ord. If, for example, a ])articular segment of the cord is diseased, this dis- order will immediately relleet itself in gi'ave disturbances of the muscles, glands, skin, bone and blood vessels in the corresponding body segment. But the spinal cord is something more than the capital of a single state. As a seat of goveriinient, it is coordinated witli many others like it, so inte- grated as to control (he federation of body segments which constitute the animal. The close connnunity of interests between the bodj' segments de- mands the closest possiMe means of cormuunicat iy disease in the white matter. tJiseases of the gray mattei', in the main, manifest themselves as dis- turliances in the specific >n', that is, disorders in the influences dependent upon the cerelnum. This lact is well illustrateil m the case of a lesion destroying the gray matter of tlie Stli eerx'ical segment, as a result of which the symptoms are i-onfined to the strui'tures in the hands and forearms. The character of the symptoms is determined liy the defects in the specific segmental functions of the gra\' matter. In contrast to tins is the much more extensive disturbance resulting from the destruction of the white niattei' of the Sth cervical segment, leaving in- tact the gray suf)sta.nce. In this case, the s\'mptoms will be manifest in somatic structui'cs at and below the level of the lesion, that is, in the hands and forearms, trunl< and legs. These symptoms take their character from the defects produced in the integrative su])rasegniental control of the liody, and represent the loss of cerelo-al control ovei' the spinal cord. The s]")ecific segmental functions of the gray matter have lucviously been discussed. When diseased oi- injured, tbe gra\' matter will be defec- THE SPINAL CORD 215 tive in some or all of its functional activities. Thus it nmy become deficient m the sjjecific function of its ventral gray column. Under such conditions the idiodynaniic, reflex, myotonic and volitional control will present path- ological changes, or it may be deficient in the specific function of its lateral gray column, in which event vasomotor and visceral disturbances appear. Usually, however, the ventral and lateral gra}- columns are simultaneously affected. The dorsal gray columns and dorsal root ganglia may become defective m their specific functions, and the symptoms will then confine themselves largely to sensory disturbances. Pathological changes in the gray commissure also bring about specific disturbances in the form of sensory changes. The integrative suprasegmental functions of the white matter have already been given m detail. When diseased or injured, the white matter may be rendered defective in some part or all of its functional activities. Pathological changes may involve the dorsal white column, and m this case the symptoms will be those due to defects in the conduction pathway designed for the conveyance of critical sensibility. The lateral white column maj^ be diseased or injured, under which con- ditions the symptoms produced would be those due to the interruption of the cerebral influence contributing volitional control to the movements of the body. A lesion in this portion of the white matter may also interrupt the pathway conveying the affective elements of sensibihty, namely, the hurt element and temperature sense, resulting in a definite group of sensory disturbances. Lesions in the ventral white column are not only less frequent than those affecting the lateral and dorsal columns, but are also less definite in their symptoms. When present, however, their essential and demonstrable defect is made apparent in disturbances of volitional control. It is a general rule that pathological processes seldom involve simul- taneously all the elements of the gray matter in the spinal cord. Infectious agents, toxic substances, and even degenerative processes seem to have a selective affinity for one or another part of the gray matter, and thus it is possible to recognize symptom-complexes or syndromes attributable to disease in the ventral gray matter, in the dorsal gray matter or in the gray commissure. Similarly, pathological processes have selective affinity in the white substance, in consecjuence of which there are syndromes due to involvement of the dorsal white column, of the lateral white column, and some, more vaguely defined, due to involvement of the ventral white column. Clinical Syndromes as a Means of Interpreting Spinal Cord Function. One of the most effective methods in the investigation of the functions of the spinal cord is the correlation of clinical symptoms with the pathologic pro- cesses which produce the well recognized spinal cord syndromes. These syndromes may be classified in three groups : 1. Syndromes of the gray matter. 2. Svndromes of the white matter. 21(> FOiai AND FrNCTJONS OF THE CENTRAL XERVOUS SYSTEM 3. Sj'ndroiDCS of the 'Jivuy and \\'lii1c matter coiubined. They are to be iT'i^ardeil as translations ' history and without previous ill- ness, on June ]l, lOKi, l:)e<;an to com]ilain of slight hratlache and fatigue toward tlic end of tlie day. U]")on putting the child to lied the mother, beli(A'ing lliat Iho l)ody was wai'incr than usual, took the tem- perature fjy rcctnin, and found it. to be bM.2°. T][r child jiassed a restless niglit, tossing and moaning in his sleep. Towai'd iiioming he liccainc quieter and slept so profoundly- thai tlic niothci' l)ecame alarmed. She finally aroused tlie baby and soon ol)ser\'i'(l Ihal there was something wi'ong witli the right arm. Upon \"\'alcliing I fie child, it liccaiiic cA'idcnt th.at hr could not move his ai'in, foi'earm al details to the case of a little girl whom he had seen the previous (lay in the house adjoining that of the patient's family, d'hc fact that another child was similarly affected next door was sugg('sti\-e of an actu.al c|")ideniic or ejiidcinic tendency. TITE SPINAL COKD 217 Examination. Upon examination made so tliat all four components of the nervous system were carefully scrutinized, the following facts were brought to light: (a) Stntiis of the So)nattc Motor Component. Testing voluntary movement and strength of the muscles of the left arm and in both legs as well as in the trunk and neck, it was found that all of tliis musculature was normal. The child had no volitional control over the right arm, nor did he make a move- ment of any kind with this part of the body when requested to do so. In other words, there was a complete voluntary paralysis of the right upper extremity. In addition to the absence of ^'oluntary control in the right arm, there was a complete lack of synei-gic and automatic associated control. The tone of all of the muscles about the right shoulder, elbow, wrist and hand was greatly reduced, wdiile normal tone was retained in all other muscle groups of the body. The reflexes, including the pectoral, triceps, biceps, olecranon, radial, ulnar and wrist reflexes, were all absent in the right arm ; elsewhere in the body both deep and superficial reflexes were normal. The alisence of tone and reflex control in the right arm occasioned such a lack of muscular resist- ance that the entire arm could be swung like a flail. If elevated and dropped, it would fall and swing much as does the arm in the articulated skeleton. At the end of several weeks, the right arm showed a marked wasting in all of its muscle groups, including the hand, forearm, arm and shoulder girdle. At this time, also, a marked loss in the normal contour of the muscle bellies was oliserved, and up(jn testing the nerves and muscles with elec- tricity, it was found that all response to the faradic current was abolished and that the anode closing contracture was much stronger than the cathode closing contracture, indicating the presence of the reaction of degeneration (R. D.). (6) Status of the Splanchnic Motor Component. During the first few days, there was little evidence of involvement of the vasomotor system; at the end of two weeks, howevei-, the arm began to assume a mottled appearance due to the congestion of blood in the cutaneous capillaries and venules. Furthermore, upon examination, it was found that the surface temperature of the right arm was two degrees lower tfian that of the left arm, of the trunk or the legs. The rest of the body showed no such change. (c) Status of the Somatic Sensory Component. The child at no time com- plained of any suljjcctive change in sensibility. He had no numbness, tmglmg, burning or any other form of dysesthesia, nor did he complain of pam. He was not at any time especially conscious of the diflficulty in his arm, and although unable voluntarily to control the movements of the right arm, he did not seem particularly annoyed or inconvenienced by this defect. Objectively, upon examination, all qualities and modahties of somatic sen- sibility were found to be intact. (d) Status of the Splanchnic Sensory Component. Tlierc was no evidence of any sensory disturbance due to disorder of the splanchnic sensory component. 218 FORM AND F(:NrTIONS OF THE CP'.NTRAI, NERVOTS SYSTEM IxTKHPRETATioN AND ANATOMICAL x\.NALYaiti. The liGadaclie, tcin- peratuio and restlessness of short duration indicated the occurrence of an acute infection which rapidly ran its course. The complete paralysis of the right nvm, so suddenly prochicod, sliowed the profound efl'ect of the disease. Tlie main lesion was somewhere in the nervous system, and thei'C was complete evidence of its focus. This was afforded l)y the fact that the final common pathway was completely blocked. The total paralysis of the right arm shnwing tlie lossof volitional control and strength of the mus(-les, while all the other muscles oi the body remained noriijal, lioth in strength and volitional control, the loss of synergic and automatic associated control, the marked loss of muscle tone, the absence of the' deep reflexes in the right Til., 'jno. — .1. Svnilronie i.f tlic viiitr;il ii.inl lateral gray (■i>luiiii!>. Ariitc aiiteriui- jiitiiiinyelitis. Red indicates l(.>\vcr iiiritiir ncuioiir pai-ulx'sis. L\ Cviiss soctiijii through i'er\-ir:il fnlargcini'iit showing the liiratiiin of the lesion m unde tiNlrrmr poUomycl- ilis: In\-ol\-('iiKTit of vt'iitial anil lateral gray columns. arm and, the ultimate loss in volume and contoui^of the muscles, together with the presence of the reaction of degeneration, indicated a lesion in the final common pathway of the .-^niiiiilir motor fiy^tem controlling the right arm. Furthermore, the reduction nf surface lemperaturi? in the right annas com- pared with the rest of the body, and the venous congestion indicating a loss of vasoi)H)tor tone, jxiinted to a disturbance in the-, final common pathway of t.ho splaiichnic motor system. The involvement of these two final common pathways points to alesion in one of two places, i.e., either in the vcntial and lalcral gray columns or in tlie periplieral nerves leading therefrom. The evidence; of circumscription of t\w lesion shows that it cannot be in the peripheral iii;rves, for tlie reason tliat were an acute infective process THE SPINAL CORD 219 to involve these siiuctures, some degree of sensory disturbance would in all probability be present. But the total absence of dysesthesia, pares- thesia, pain and objective sensory disorders, suffices to rule out the possi- bility of a lesion in the peripheral nerves. This evidence of circumscription also draws the boundaries of the lesion by showing that the pathwaj^s for all types of sensibility are intact in the spinal cord and that the pathways for suprasegmental motor control are still eflective. The boundary line thus drawn limits the lesion to the ventral and lateral gray columns of the right side of the cervical enlargement of tlie spinal cord. DiAGNOSLS AND PATHOLOGY. The diagnosis of the condition is acute anterior poliomyelitis. The pathology of this lesion is an acute inflammatory reaction involving the neural elements in the ventral and lateral gray columns in such a way as either to destroy or gravely impair the large motor cells which serve as the neurosomata of the final common pathway. This disease has the tendency to occur in extensive epidemics. Nomenclature. Acute anterior poliomyelitis is also known by several other terms. It is sometimes spoken of as infantile flaccid paralysis, infan- tile spinal paralysis, "polio", epidemic spinal paralysis, and the Heine- Medin disease. Variations. Acute anterior ]ioliomyelitis varies greatl}^ in its mode of onset as well as in its course and duration. In most cases, the initial paraly- sis represents the maximum of involvement and is followed by greater or less recession, leaving a residual permanent paralysis. In other cases the paraly- sis is progressive, or there may be a recession of the initial paralytic symp- toms so marked as to result in an almost complete recovery of the patient. The most common form of the ])aralvsis is found in one upper extremity. Often the arm and leg upon tlK> same sitlc are affected, giving the appearance of a flaccid hemiplegia. One leg alone may l)e involved, or only a portion of the leg, more especially the muscle group below the knee, and in particular the anterior tibial or peroneal groups; frequentl^y both legs are involved with equal severity, and in rarer cases the musculature of the entire body, in- cluding the extremities, trunk and neck, presents a profound degree of paraly.sis. Sum:\iary. The essential clinical fcatuies of acute anterior polio- myelitis are: { 1 ) Loss of idiodynamic, reflex, tonic and volitional control in the spinal cord .segments involved by the inflammation, resulting in the following changes in the corresponding muscles: (a) Atrophy with loss of contour and the presence of the reaction of degeneration. (6) Loss of the deep and sujierficial reflexes. (c) INIarked loss of muscle tone. (d) Paralysis due to interruption of the final common pathway, which 1 (locks the transmission of volitional impulses; a flaccid paralysis. (2) Vasomotor paralysis, as shown by the mottling of the skin and the reduced surface temperature of the afi"i>cted parts. 220 FORM AND FUNCTIONS OF THE (JENTKAL NERVOUS SYSTEM (3) Rfsfric(it)ii nf tlir sonialir ami splaiichnif motor s.ymptoms to the area, corn'spoiidinu; (o the spinal cord scR'niciit im'olved. (4) i\.l)S(')ic<' of sensor\' disi iii'linin'-os. Syndrome of the Dorsal Gray Matter: Dorsal Root Ganglion. His- TouY. A Vdiiiiu; woman, lliirty-two years of age, liogan to complain of pain between (he shoulders, along the hacbof the left arm, and on the left side ol' the chest. Slic felt slightly indisposed, had some fever and headaclie with loss of appclile lasting for sevei-al days. During the second night of her illness, she was awakened by more severe and bui-ning pain in the areas already mentioned. In the morning it was found that she had a ,1 B Vic. 2tO. — A anil j!. S\-[iiliiiiiii' lA' I he dnrsal root f^Mii^lidn ; Acute postcriijr poliomyelitis: (Herpes Zoritei). lii'il iMcrirjlcs ;iic:i of jiaiii, IiA')-)alL;csia and Inpesthesia. series of small ])list<'rs exlending from (lie mid-dorsal line im the left side around the chest to the iiiid-veni ral line, "hliis zone roducing an irritative disturbance in the ganglia involved. This irritation is often followed by degeneration, thus explaining the original iiritabilit}' in the cutaneous areas followed by a general reduction in all types of surface sensibility. Nomexclature. This disease is known as acute 'posterior polw- inAjelitis, herpes zoster and sJungles. Vari.\.tions. Pain is a constant symptom in this disease. The her- petic eruption may be a scanty or a profuse crop of bhsters. The distriluition of Ijoth i)ain and the herpetii; zone dejiends upon the dorsal root ganglia which are involved in the inflammatory pi'ocess. This is most common about the trunk, but ma}' o<'ciu' ujion the face, the neck, the arms and the lower extremities. Summary. TIk^ essential clinical features of acute jjosterior ])olio- myelitis are: (1) The sudden ap|)carance of localized pain in regions limited to one or more dermatomes, and always including the anterior and posterior derma- tomie divisions. This pain is accompanied tiy acute objective irrital.iihty, which, however, is suljsequently replaced by some diminution in all types of somatic sensation. (2) The coincidence in the d<'rmatomic regions of the pain of a crop of small blisters, each of which is exti'cmely sensitive to fourh and pressure. (3) The al)sence (->f all e\'ideiic(' "f nicjtor distin't)ance, with the possible exception of a slight inci'eas(> in the reflexes in the affected area, and intact somesthetic sensibility with the exception of the dermatomes invoh'<>d in the lesion. Syndrome of the Central Gray Matter : The Gray Commissure. History. A young man, (went>--t\vo yeais of age, oliscrved that he frequently burned the tips of his Angers of both hands when lighting a cigarette. He was unable to understand, however, why it was that even though the lighted match oi- the lighted end of the cigarette came in actual contact with his skin, he experienced no feeling of pain. In the course of the next few months, he observed that ha had lost his usual sensiltility of pain in the tips of the fingers, as well as in the hands and forearms, altliough in these latter ai-eas the dinniiutioii in sensoiA' acuity was less mai-ked than in the fingiu's. He also (jbsei\'ed iliat he could put his liands in extremely hot water without experiencing aii>- discomfort. Sevc^ral ulcers developed (in the tips of his Angers, probalily m areas wliich he had burned with his cigarettes. The patient c(juld not understand why these ulcers were so long in heahng, but explained the fact to himself on the ground that he had [irob- ably injured the ulcerateil ai'cas fi'om (ime to time in couseipii'iice ol' liis hick of feeling in the fingers. THE SPINAL CORD 223 Examination, (a) Status of the Somatic Sensory Component. Sub- jectively, the patient complained of little; he was not conscious of any tin- gling, any numbness or burning in his hands. What had impressed itself Fig. 211. — A and B. S}-iuh'ome of tbo central gray niattei- — the gray commissure. S^Tmgo- myelia. Red indicates analgesia and thernianesthesia ^^'ith retention of rliscnmina- tivc sensibility. S^-ringomyelic sensory dissociation. C. Cross section through fir.st thoracic segment showing :the location of tlie lesion in Si/ringomyelia: Involvement of the graj- commissure. upon him, was the fact that things which formerly hurt liim no longer did so, and he seemed to have lost perception of hot and cold. Objectively these observations were borne out .by tests. The application of hot and cold test tubes to the skin over the fingers, hands and forearms uniformly brought the wrong response, as the patient was unal^le to dis- 224 FORM AND FUNCTI(JN8 OF THE CENTRAL NERVOUS SYSTEM tiiiL;:ni,-;li tho (einiicraturc (if I lie ol)jeft applied, even lhoui;;h tlie tubes were fille'stem. IXTEKPHETATKJN AXI) AxATOMICAL AXALYSI.S. The llistorv of tllis ease indicates a chronic and progressiA'e lesion. Tlie e\'idence of the focus of the lesioTi eleaily shows tliat the somatic sensory eom|)onent had lieen iuAoh'eil by a progressively destru(.'ti\"e lesion. The distril)Ution of the lesion and its limitation to the dermatomes supplied by the 6th, 7tli and Sth ceivical and 1st thoracic segments of the spinal cord indicate a spinal le.sion in or near tlie segments already eiuimerated. The evidence of circumscription of the lesion, on account of the marked sensory dissociation, shows that the pathological process is in the spinal cord segments rather than in the |)eripheral nerves, the dorsal root ganglia or the dorsal roots themselves. The disturbance could not l)e in the dorsal gray column, because this part of the nervous S3'steni probably serves as a relay for all types of sensibility; neither is the disturbance in the ventral gray column, since there are no motor ,sym]itoms; nor is there any evidence of invoh'ement of the doi-sid, latei'al or Aciitival white columns. For these reasons, the dtsturbance must be in the central gray matter, in which there occurs a complete crossing of the fibers designed to convejr to the brain sensory stimuli concerned witli the (em]X'ra( ure sensibilit>', and also carrying THE SPIXAL CORD 225 the hurt element of sensation. A lesion in this position would interrupt the pathway for pain and temperature and thus produce the peculiar tj^pe of sensory cUssoeiation which inarks this disease, syrmgomyelic sensorij dissociation. Diagnosis and Pathology. The diagnosis in this ■ case is sunnge- vnjclia, (syrinx, tube; mijchrii, cord). The lesion which causes this dis- turbance is a destructive one, Ix-gmning usually as an increase in the cells in the central gray matter which subseciuently break down at their center, giving ri.se to a cyst formation known as a syrinx, which, Ijy its pressure, destroys the crossing fibers of the pain-temperature pathway, thus explain- ing the more or less symmetrical involvement of the two sides. Nomenclature. Syriiuionujelia is also sprtken of as central gliosis. It is proljable that in its incipiency the disorder is due to an increase of the neuroglia or ependymal cells in the central givay matter which subsecjuently give rise to a. cyst-like dilatation. Variations. It is only in its early stages that syringomyelia mani- fests the limited clinical symptoms enumerated in this patient. The sub- sequent course of this particular case developed some of the more important variations to which the disease is subject. This jjatient later presented a marked atrojihy in tlie hands and in the forearms. 8uch a change is indica- tive of tlie extension of the cyst so that it involved the ventral gi'ay columns. Subsecjuently the patient noticed a stiffness in his legs, and great difficult}' in walking. He had, in effect, a spastic paraplegia with an increase of all the deep reflexes, loss of tlie su])crficial reflexes, and the appearance of such pathological reflexes as the Baljinski and crossed ]ieriosteal reflexes. These latter changes indicated tlie extension of the cyst into the lateral white columns. Ultimately there was a marked diminution of somesthetic sensi- bility, involving critical ciualities in 1 he trunk and legs, thus showing that the cyst had invaded the dorsal white columns of the cord. .These ai'e Init a few of the many variations to which syringomyelia is sufiject, due to the irregular extension of the slowly dilating cyst. Usually the CA'st forms at the leA-el of the cervical segments of the cord. More rarely it Ijcgins lower down in the thoj-acic and even in the lumliar segments. Under sucli circumstances the s>-iiipt<)ins take tlieir character from and haA-e their distri))ution in accord with the level of the pi'imary involvement. SuMM.iRY. Tlie essential clinical features of syringomyelia are: (1) The loss of pain and temperature sensibility with the retention of critical tactile, joint, muscle, pressure and vibratory sensifiility (syringo- myelic sensor}' dissociation). In addition to this, as a result of the extension of the lesion, there is usualh' a combination of: (2) Atrophy and other trophic changes in the parts supphed Ijy the segments of the primaiv' lesion, and (3) Spastic paralysis of the upper motor neurone type in parts suiiphed by segments below the level of the lesion. 22() FORM AND FUNCTIONS OF 'I'HE CENTFlAL NKlrt'OI'S SYSTEM ■SYNDKOME.S DF TiTK WHITE MATTER Syndrome of the Dorsal White Column. History. A A\(iinan of middle life i began to notice some numbness and tingJiiiK in hei fingers. Slie had increasing difficulty in the performance of finer skilled acts, such as sewing and playing the piano. She found that hei- hands were not steady; that she could not, on this account, thread her needle or strike the proi)er notes on the ke>i)oard. In the course of two months, a similar defect became apparent in her lower extremities. Hci' feet felt numb and cold. There was a tingling sensation in her legs and thighs. In walking, her steps became inaccurate and she was compelled to watch her feet constantly in order to keep from falling. She had no proper sense of motion in her legs, and as she walked she staggered and swayed from side to side. She had not lost strength in her limbs, but she did not possess the necessary feeling in them to guide her locomotion properly. Her con- dition in these respects l)ecame gradually worse. Examination, (a) Slutus of the Somatic Motor Component. Voli- tional control and muscle strength were found to be normal. Equilibrator>" control in all tests showed a marked defect, as did also synergic control. (.)n the other hand, automatic associated control was normal. There was a consideraljle reduction in the myotonus and also in the reflex activity. Idiodynamic control was normal in all respects. (6) Status of the Somatic Sensonj Component. Tlie jiatient's complaint comprised disturbances in sensation descriljcd as tingling, munlniess, a sense of cold and improper recognition of feeling in the limbs, all of whidi mdicateil the presence of marked dysesthesia (defective sensibilityj. (Jbjectively, she showed a decrease in the muscle-joint scnsiliihty, in vilnatory .sense, in tactile discriminatif)n and in deep and superficial pres- sure. Light stroking with a camel's hair brush or cotton wool was often inaccurately interpreted over her legs, arms and trunk. The neck, head and face showeil no sensory disturbances. Temperature sensil.iility and affective tactile .sensibility, togetlier with the hurt element, were retained. (c) Status of the Splanchnic Motor Component. This was normal. (d) Status if the Splanchnic Sensenii Component. There was no evidence of any pathological change in this element of the central nerv(.)us system. Interpret.ation and Anatomical Analysis. The history indicates a slowly progressive and degenerative lesion. The evidence of tlie focus of the lesion places the pathological process in the .somatic sensory component. The allomeric thstribution indicates a suprasegmental involvement. There is sume interruption in the flow of in- fluences dependent upon the cerelirum. This may Ije eithei- in the brain or in the spinal cord. Lesions in the brain are usually unilateral; in the spinal cord they are more apt to be bilateral. The bilateral distribution of the s^Tiip- toms in tliis case, therefore, points to the spinal cord. The defects in discriminative .sensiliility with intact affi'ctixc sensil)ili(y indicate the dorsal wliiie column. S\-mptomalically, 1hesensor>- dissociation THE SPIXAL CORD 21'/ is in contrast to that ol)servcd in s,\ riiiu;oiii\'elia., for lieie [laiu and t(nii])era- tiire arc unaffected. This t>'pe of sensory disturbance is known as tabetic sensory dissocidtion. Tlie hjwered reflexes and diminislied muscle tone point to some defect in tlie reflex arc wliich may f)e explained b}' involvement of the reflex collaterals passing in the entrant zcnie close to the dorsal columns. The evidence of circumscription of the lesion exempts the remaining white columns of the cord. There is no indication of loss of v(jlilioiial conti'ol or muscle strength. The loss of synergic control is duo to the lack of proper muscle and joint sensiliility. Thca'c is no indication of defect in the ventral, lateral or dorsal gi'ay coluniiis, nor in tlie ccniral gia}' conunissure, h'lr.. 212. — A. Syndrome of the dor.sal wliite columns; dorsal spinal sclerosis. Reel indicates loss of tactile, superficial and deep, muscle-joint, vibratory sensi- bility with retention of pain and temperature sensibility. Taljetic sensory dissociation. 73. Cross section through the cervical enlargement sliou- ing the location of the lesion in dorsal spinal srh.r- oxis: Involvement of the dorsal white colnnins. nor in the dorsal root ganglia. The focus of the lesion is, therefore, m the dorsal white columns of the spinal cord. Dt.\gnosis and Pathology. The diagnosis in this case is dorsal spinal sclerosis caused by degenerative changes in the dorsal white columns. The lesion is situated in the cervical enlargement. NoMENCLATUKE. This discasc is known as dorsal spinal sclerosis, primary dorsal sclerosis, sensory spinal ataxia or spinal tabetic sensory dissociation. Variations. The distribution of the sensory disturljance in this disease is subject to considerable variation, dependent upon the height of the lesion. Usually the focus of tlie lesion is in the cervical region. It ma>-. however, l.)e lower down, involving either tlie thoracic or upiier lumbar segments of the cord. 228 FORM AND FITNIJTIONS OF THE CENTRAL NERVOUS SYSTEM Summary. The essential fc;itur(\s of dorsal spinal sclerosis are: (1) Loss of critical scnsil)ilit3' in the legs and arms witli the retention of pain and temperature sensibility (talietic sensory dissociation). (2) Loss of coordination, prodncinp; ataxia in locomotion and in other skilled acts. (3) Reduction of the deep refle.xes and muscle tone. (4) Normal m\'(isthenic and myotrophic condition. Syndrome of the Lateral White Column. History. A man, aged thirty-foul', who had always ])een actu'c in business, noticed the gradual dcveloiinicut of fatigue ui)on walldng and especially upon going upstairs. His legs felt heavy and stiff. Li the course of several months this stiffness tiecarne nmre pronounced. He suffered no pain and no si'usory disoriler of an>' kind. His only inconvenience^ was a greater difhculty in locomotion occasioned by the stiffness in his legs, tbadualh' -this stiffness incicased until lie was unable to lift either foot from the gi-ound in wajlcing; he dragged each foot. Li fact, his entire leg was stiff and moA'cd as one ])iec<' fi'oin the hiji to tlie ankle. The stiffness increased so much that the adibietor muscles lii'ld his thighs closer together, and in walking one io(]1 was passed in fi'ont of the other, producing what is known as (he "seissoi'-gait . " This soi'l of cross-iegged progression was ulti- m;iti'ly attended !)>• a kind of sprmg-lilvc osrill:ition m the entire boch', due to the fact that at endi s!ep the foot was nio\-ed by a clonic contraction of the muscles. In acts other than those concericil in locomotion it was difficult for the paticmt to mo\'e lus ft-ei, his legs or his thighs. Xo other motor or sensory elements in his liody weie affected. His condition grew progressively worse and he finally became ].)edridden. ExAMi\.\Ti'pe could be elicited by pi'oper testin!^'. The myo- tonic colli rol of the iiniscles has alre;idy lieeli referred to as show ing a mai'ked hyperlonus in llie muscles of I he lower extreinities. The reflexes were cor- respondin};ly increased in (heir .acliAaty, i'speciall\' those at the knee aiul ankle. Certain pal l!olo,i;ical rellexes wei'e also obser\"e(J, among them lieing a patellar and ankle cliniiis, tlie ISabinski and the crossetl periosteal retlcx. The abdoiiiiii.-il rellexes were all absent. The idiances firing to light any change of som- esthetic sensibilitj'. THE SPINAL CORD 229 (c) Siatus of the Splanchnic Molar Component. There was no defect observed in this element of the nervous system. {d) Status of the Splanchnic Sensory Component. There was no evidence of pathological change in this element of the nervous svsteni. Fic. 213. — A and B. Syndrome of the lateral white column: Primary lateral sclero.sis. Red indicates a spa.stic parajjlejiia wilh increa.>^e in. the deep reflexes and patho- logical reflexes. C. Cross section through thoracic segment showing the location of the lesion in primurij lateral ■•icierosis: Involvement <>i the pyramidal tracts. IxTERPEETATiox .WD AxATO^rTCAL AxAT.TsVs. Tliis case indicates a chronic progressive degenerative process affecting the ner\oiis sysleni. The evidence of the focus of the lesion indicates an involvement of the somatic motor component. The fact that this in\'olvement is clinicall>- 23(1 FOini AM) FI'NCTIOXh; OF THE CP^NTRAL NERA'OUS SYSTEM liilatcial ]:)()iiils t'pe of paralj'sis and the distril)ution of this paralysis may vary somewhat with the height of the lesion. It lart'ly in\'ol\'es the cervical portion of the spinal cord. Summary. The essential fi'atincs of primary lateral scleiosis arc: (1) Spastic ])araplegia. (2) Inciease of the d(/ep ii'ticxcs, aiipearancc abinsl stairs, and that in walking on the level there was a tendencj- for one foot to cross in front of the other. This she could prevent only by an extreme effort of the will. On certain occasions when sitting, she noticed that both legs trem- bled and shook, especially if the foot was placed in such a waj' that the heel was lifted from the floor. She finally l>ecame .so anemic and physically de- pressed that it was necessary for her to remain in bed. In several months her general condition improved and she was able to get up and go about again. At this time, she noticed a marked change in locomotion. On attempting to walk, she had a pecuhar sensation as of pins and needles in the feet and legs, and seemed to have an imperfect perception of how her muscles were acting, so that in walking it was necessary for her to watch the ground with care. If she were inattentive in this regard, she began to stagger, even to lose her balance and fall. Her legs were no longer s'tiff, nor did she have any of the peculiar tremor which had been noticed, especially when sitting down. .Vn examination of her blood at this period showed that she was suffering from perniciims anemia. ExAMiN.\TiON. Several examinations of the patient during the course of her disease showed the following changes: (a) Status of the Somatic Motor Component. During the early stages of I he disease, volitional control was appreciably defective, as was also the strength of the muscles in the legs. The gait was spastic, due to a marked increase in the tonus of the muscles. The deep reflexes were all more active than usual; there was patellar and ankle clonus, a bilateral Babinski and a, bilateral crossed periosteal reflex. Eciuilibratory and sj-nergic control were both normal in so far as they were not impaired by this spasticity of the muscles . Idiodynamic control remained normal throughout the entire course of the disease. During the second stage of her disorder, particularly during the period after she had recovered from her first acute anemic depression and was able to walk again, the symptoms of muscular spasticity and defective voli- tional control were replaced or overshadowed by a loss in equilibratory and uon-equilibratory coordination, and also by the complete disappearance of all the deep reflexes. (b) Status of the Somatic Sensory Component. In the early stages of the disease, the patient showed httle or no subjective or objective change m somesthetic sensibility. Subsequently, however, such changes were ])resent in marked degree. The patient complained of certain dysesthe- sia, principally numbness and a feeling of cold in the legs. No pain was complained of at any time. (3bjective investigation of sensibihty showed that all types of critical sensation were seriously affected, including muscle, joint, vibratory, and tactile discrimination. To some degree also affective •sensibilitv was involved, pain and temperature stimuli lioth showing a 232 FORl\r AND FUNCTIONS (_)F THE CENTRAL NEltVOUS SYSTEM marked rctaidatioii in transmission as well as crtnsiderablc confusion in perception. (c) Status of the Splanchnic Motor Component. No changes were ob- served in this part of the nervous system. (d) Status of the Splanchnic Sentiory ('onipoiirnt. There was no evidence of pathological alteration in tjiis component. Interpj'.etation ANT) ANAT0nrTf,4L iV\ALYsis. The history of this case shows a chronic progressive involvement of tlie nervous system in consequence of or in crniiliination wilh [leiiiicious anemia. Tlic evidence of the J'ocus of the li'sion indicates a successive involvement, first, rif the somatic iriotor <'oirip(>iient, and suhsequently, of the somatic Fill. 214. — .4. Syndrome of the dorsal and lateral white (■(ilunms: Combined sclerosis. Red indicates ataxic tetraplegia with Ios.s of volitional control, ataxia. \dt)mate sujiprcssiori of tlie deep reflexes and a diminntion in iliscriviiinativc sensibility. Pain and ti-mper:iture are l:>ut little afl'ei'ted. B. Ci'dss section througlij .tlioracic segment showing the Inralinniif thi' lesion in fo»('i(/('.'/ .^r/i/i.i.si.s; Involve- Hieiit III' tlic diirsal \vl)ite coliuuiis and pyramidal tr.acts. .sensory component. The bilateral disti'ihutnin of this disorder to both legs would indicate a cord rather than a cerel.iral lesion. The symptoms in the early stage of the disease were those of a, spastic spinal paraplegia, indicating a lesion in tin- lateral \\'hite column. Latei- the symptoms were those of a spinal sensory .-rt.'ixi:!, thus poinling (o a disorder winch combines the characteristics of jii'ima.ry lateral sclei'osis and primary dorsal sclerosis. I'he e\'ideni:'e of circumscription of the lesion indicates that the ventral gray column, the doi-sal gray column and doi'sali'oot ganglia, were not alTccted 1iy tJie ])atliological changes. Tlic comdusion, therefore, is that the patho- logical alterations wei'e confined to the la1ei-al and dorsal white columns. In the latter columns, tlie ]iyramidal tracts and probably the si.iino-thalamic tracts were affected, while all of the tracts in the dorsal columns were in- THE SPINAL CORD 233 volved, together with reflex cohaterals cropsing in the entrant zone of the dorsal root. Diagnosis and Pathology. The diagnosis of this condition is combined sclerosis. This is due to tlie patlrological alteration in the pyram- idal tracts and in the dorsal white columns, almost symmetrical!}' and bilaterallj' disposed. It has been assumed l)y some authorities that perni- cious anemia determines a toxic condition as the result of which degenera- tive changes take place in the central nervous system. There are those, however, who maintain that the pernicious anemia is coincident with the changes in the spinal cord. Nomenclature. This disease is known as comhined sclerosis and as lateral and dorsal sclerosis complicating pernicious anemia. Variations. I\Iany cases of this disease show an involvement of the arms as well as of the legs. When this latter is the case, howcA'cr, the changes in the arms are largelj' confined to disorders in sensil)ility. The disease is subject to marked fluctuations, the patient presenting periods in which all the symptoms are at a minimum, and others in which each sjmiptom is developed to an extreme degree. Summary. The essential clinical features of combined sclerosi's are: (1) The successive appearance of primary lateral sclerosis shortly followed by all the symptoms of dorsal spinal sclerosis; that is to say, a spastic spinal paraplegia complicated by spinal sensory ataxia. (2) The absence of all evidence of involvement of the ventral gra>- column, of the dorsal gray column or of the dorsal root ganglia. Syndrome of Friedreich's Ataxia. History. A girl, eleven years of age, began to notice that she stumbled and fell in play. This difficulty slowly increased until it became apparent even in walking. She was con- scious of considerable diflaculty in movements of the liands and fingers, especially in writing and needlework. This condition grew progressively worse for about a j'ear, at which time her younger brother, nine years of age, began to complain of the same difficulty in running, walking, and the finer movements of the hands. Enajiination. "When examined at tliis time, the girl showed the following conditions: (a) Status of the Somatic Motor Component. The volitional control and muscular strength were nearly normal, but the equihbratory and non- equihbratory control were both much impaired. All tests for equihbratory coordination showed marked defects. Non-equililjratory coordination, hke- wise, developed extreme ataxia. Automatic associated control was nor- mal. The muscle tone was much reduced in the arms and legs, but much increased in tlie feet, where it produced an extreme arching known as "pes cavus." The deep reflexes were feeble in the arms and absent at the knee. Of the superficial reflexes, the aljdominals were absent, but a Baldnski was present on Ijoth sides. The idiodynamic control was normal. (b) Status of the Somatic Sensory Component. The patient complained neither of pain nor of any other subjective change in sensibility. Upon 234 FORM AXD FUNX'TIOXS OF THE CENTRAL XERVOITS SYSTEM examination, however, a slight diminution in aU types of sensation was found, hut more marked in tlic muscle, joint, tactile discrimination and vibratory sensiVlilit^-. This defect was limited to the legs and feet. Fic. I'lTi. — ,1 and B. Syndinini- of I'l-irdrcirli's ataxia. \U-i\ indicates I'nuilibratdry and non-equilibratoiy ataxia and a lis,. nre el' tlic knee-jerk. Blue indicates in addition to the preoedinfi; a diiiiiniitiDU in all types of sensiliility, especially the discrimin- ative tj'pc. >'. Cross section through the cer^'iciil enlarifrinent showing the location of the lesion in Friirlreich's niaxiir. Involvement of llie s])iiiii-eerelielhir and pyramidal tracts and the dorsal white columns. (c) Status of the S/)Il\eiiient of jiyramidal tracts and ventral gray eohunns. arms were mtudi wasted and presented the r(\ietion of degeneration, to- gether with fibrillary tremors. No such changes were apparent in the lower extremities. (6) Status of the Somatic Sensori/ ('Diiijxiiu'iit. ^fliei'e were no patho- logical changes in this conii^onent. (c) Status of the Siilinitli nic Miitvr Cum i/oiiml . This was normal. (d) Status of the Sjihiuch mr Seiisor/i Componcut. Thei'e w:is no evidence of pathological alteration in this eh^ment of the nervous SA'stem. Ix'TEKPKKTA'rjox ,^ ,Mj Ax -\ii ijiicAL AxALYsis. The history is that of a, chronic, progressive dise:ise, degenerative in its character. Tlie evidence of the focus of tlie lesion sho\'C's that the pathological pro- cess lias involved the somatic motor component in tlie gray ;ind the white THE SPINAL CORD 237 matter. The location is in tlie cord, because of the bilateral distribution of the sj^nptoms. The disturbances in the arms are due to involvement of the grajr matter, while those in the legs are caused b,y defects in the white matter. In the arms there is loss of vohtional control and idiodynamic con- trol. The spastic paraplegia is indicative of an involvement in the lateral white column, especially affecting the p.yramidal tracts. The evidence of circumscription of the lesion shows no sign referable to the dorsal gray or white column. The lesion, therefore, involves both lateral white and ventral gray columns. Diagnosis and Pathology. The diagnosis in this case is amyo- trophic lateral sclerosis. The pathology of the condition is a progressive degenerative change, first involving the pjTamidal tract in the cervical segments and then extending to the ventral gray columiL Nomenclature. Airnjotrophic lateral sclerosis is also known as spkislic spinal paralysis with atrophy. Variations. The degree both of the atrophy and the spastic paraly- sis varies considerably in different cases, Ijut in all instances the diagnosis demands some CAddence indicating a lesion affecting simultaneously or consecuti"\'ely the white matter of the lateral column and the gray matter of the ventral column. Summary. The essential clinical features of amyotrophic lateral sclerosis are: (1) Spastic paralysis of the legs with pathological and increased deep reflexes. This includes the ankle clonus and Baljinski. (2) Atrophy with reaction of degeneration and filn-illary tremors in the arms, forearms and hantls. (.3) Increased reflexes in the arms. (4) Absence of sensory changes in any part of the body. Syndrome of Hemisection of the Spinal Cord. History. A sohher, shot in the back by a machine gun, was found upon operation to have sustained a fracture of the lamina of the sixth thoracic vertebra upon the left side. As ai'esult of tJiis injury, a sharp spicule of bone had lieen driven forward in such a way as to cut completely through the left half of the spinal cord. In conseciuence, he had a complete paralysis of the left leg. Examination. On examination t\v(.) months after the operation, he showed the following: (a) Status of the Somatic Motor Coinpoiiriit. The patient suffered from a complete loss of all volitional control and muscle strength m the muscles of the left leg. The other musculature of the body was normal. There was a marked increase in the tone of all the muscles of the left leg, together with an increase of the deep rellexes, incladmg an ankle clonus and a Babinski. The muscle tone, idiod3aiamie control and reflexes elsewhere in the bod.y were normal. (6) Status of the Somatic Soisunj Component. The patient complained of no sul)jectiA-e alteration m sensiliility. Upon examination, it was found 23S FORM AND FT^NCTIONH OF THE CENTRAL NERVOT-,S SYSTEM that objectively lie liad a coinplete loss of tactile, joint, muscle, and vibra- tory Sense, as well as of tactile discrimination in the left leg. Pain and tem- perature sensibility in (he left leg reniaineil intact. In the right leg, howevei-. Fk:. 217. — ,1 :iii(l I!. SAiidi-onio of hciniscction (if the curd-. Syndrome of Brown-Scquard- lifd indiratrs :i sjiastir iiioiiiiiilegi;! '"'f tbr- left leg w-ith a complete loss ot volitiona control and the ijresenee of alinormal rotlcxes, n\ addition a complete loss of the discrimative tY]ie.s of sensibility wil li areteiitioii of the alTeelive types of sensibility. Bine indicates a complete loss of affectivr sensilnlity, pain and teiiiperatnre. Green indicates a coniiilcto loss of disci'iminatiA'e sensibility. C. Cross-section through the sixth thoracic segment showing the location of the lesion in the syndrome of Brown-Siqimrd: Involvement, hemisection of the cord. wink- there was a remplete retention of joiut, niiisrle, \ibratory and tactile disci'iniination. there was an entire loss of pain and teniperalure sen- sibility. The zone c)f this disturbance upon both sides exicndeil to a li^\'el upon the ti'iiiik eoiTcsponding to tlie Sth thoi'acie derniatonie. THE SPINAL CORD 239 (c) Status of the Splanchmc Motor Component. This was normal. id) Status of the Splanchnic Sensory Component. There was no evi- dence of pathological change in this component. Interpretation and Anatomical Analysis. The history shows the case to be one of tramnatic incidence. The evidence of the focus of the lesion indicates that the injury affected the somatic motor and the somatic sensory components. This evidence points directly to an interruption m the lateral and dorsal white columns, including the pyramidal and spino-thalamic tracts, together with the tracts of Goll and Burdach. The defect is limited to the left side of the cord. The evidence of circumscription of the lesion because of the absence of any chsturbance in critical sensibihty and absence of spastic paralysis upon the right side of the body, and the presence of pain and temperature sensibihty upon the left side, indicates that the right half of the cord is still intact. There were no signs referable to the ventral or dorsal gray matter, nor to the central gray. Diagnosis and Pathology. This is known as the syndrome of hemiseclion of the cord, and is usually due to the partial separation of the cord by trauma. Nomenclature. The syndrome of hemisection of the cord is also known as the syndrome of Brown-Sequard. Variations. The degree of paralysis, as well as the sensory dis- orders, depend upon the extent, level and angle of the hemisection. Many variants of this syndrome have been clinically noted. Summary. The essential clinical features of the Brown-Sequard .syndrome are: (1) Spastic paralysis and loss of critical sensibihty ipsilateral with the lesion. (2) The loss of pain and temperature sensibility contralateral to the lesion in ai-eas corresponding with but opposite to the paralj-zed parts. (3) The absence of sensory and motor disturbances in other parts of the l)ody. Syndrome of Complete Section of the Spinal Cord. History. A soldier shot in the back was immediately paralj^zed in both legs and had com- plete loss of sensation in the lower part of his body and in both legs. He also lost control of the bladder and rectum. At operation, several days later, it ^'^•as found that the bullet had passed in such a way as to cause complete separation of the spinal cord at the 9th thoracic segment. Examination. When examined two months after the operation, he presented the following condition: (a) Status of the Somatic Motor Componerit. There was a- complete loss of volitional control and muscle strength in both legs. The patient was absolutely unable to make any movement with the muscles below the level of the umbihcus. The volitional control and muscle strength in the other muscles of the body were well preserved. There were no defects of eqiuhbra- 240 FORM AND FXTNCTIONS OF THE CENTRAL NERVOUS SYSTEM tiny or synergic coiitrf)! in the niutsfliw innervated l)y segments above the level of the lesion, while the entire aljsence of all volitional control made it iinpossilde to estimate the status of these functions below tlie lesion. The muscle tone in all the groups of muscles in both lower extremities was dis- tinelly increased. The legs were held partly in flexion and rigidly adducted. All ol' Uw deep rcHexes were extremely active. There was a l.iilateral patellar and ankle clonus and a ])ilateral Babmski. The abdominal reflexes were absent. The reflexes m lioth upper extremities were active and eciual. They manifested no p;i(]iol(igic;d cliange. The idiodynamic control of the muscula- .'1 B l''ii;. L'lS. A Mini I!- S>'iMjriiiiio (if r(iiii]ili'tc .scrtinn of tlier^])uial cord. lirJ luilicates com- plete iiar;(l>-«is of tlir \ir>i]\ anil li'i;s; ('nni]ilete loss of all ty]5es nt iliscriiiiinative and affective scusilalily ; los^ (il hladdcr and rectal control. lure of tlie \"\-lii)lc Ijddy at this period \\'as noi'nuil. I'hcre was no reaidion of ilegeneratioii, lait III lie \"\'nstiiig dI' the muscles, a slight hjss (.)f contour in the mus(de bellies and no librillary tremors. ill) Stains: iif tli( iSinnnlic Sciisuri/ ( 'itiii jiiiiicnt. The patient coni|")lained of certain sens()r>- distuib^mces; he had lnsl all perccjition of tlie position of his limbs and said he felt as if his legs lin.d lieen didaclied from his flod^^ He complained of a, slight |)ain in Ihe liaidv in the region iif the operaliA'c wound. Objcctiveh', thiae was fouml to be cnmplele loss of all tyiies of sensi- bility in all ihe (Uaniatomcs up to and including th(> l)lh thoracic dermatome. THE SPINAL CORD 241 (c) Status of the Splanchnic Motor Component. There was complete loss of control of the l)ladder and rectum and marked evidence of reduced trophic resistance of the skin which showed a tendency to decubitus (bed sores). (rf) Status of the Splanchnic Sensory Component. There was no evidence indicating pathological alteration in this part of the central nervous system. Interpretation and Anatomical Analy.sis. The history shows the case to Vje traumatic in origin. The evidence of the focus of the lesion indicates a level of the spinal cord with the upper limit of the injurj' at the 9th thoracic segment. This is substantiated by the complete absence of function in the white matter of both the lateral and dorsal columns below the level of injur}-. The evidence of circumscription of the lesion indicates that the spinal cord above the 9th thoracic segment is functionating normallj'. Diagnosis and P.\thology. The diagnosis of this condition is complete traumatic separation of the spinal cord. The pathology takes its character from the destruction occasioned by the injury. Nomenclature. This condition is known as complete traumatic severance or separation of the spinal cord. Variations. The variations of this syndrome are numerous, the two chief types depending upon the nature of the injury which produced the disorder, and the time after the injury at which the patient is seen. Crush- ing injuries of the spinal cord not only cause pathological changes at the site of the injury, but also render the cord abnormal for a considerable dis- tance both above and below the seat of the injury. Incised wounds are much less likely to have a diffuse effect upon the cord than the crushing injuries already mentioned. Cases of the diffuse type usually show a more or less complete flaccid paralysis during the entire course of the disease. In some instances, however, this initial fiaccid paralysis may be replaced by spastic paralysis with increased reflexes, clonus and Babinski. The appearance of spastic paralysis following complete separation of the cord due to incised wounds and bullet wounds is much more rapid than in the case of crushing injuries. These two elements, namely, the character of the trauma producing the lesion, and the time elapsed between the receipt of the injury and the examination of the patient, have led to much con- troversy concerning complete severance of the spinal cord. Summary. The essential clinical features of complete severance of the spinal cord immediately after the injury are: flj Immediate complete flaccid paralysis of all muscles below the level of the lesion. (2) Immediate complete loss of all types of sensibility below the level of the lesion. (3) The loss of bladder and rectal control. (•4) Normal sensory and motor conditions above the level of the lesion. The essential feat'iu-es of complete severance of the spinal cord in cases seen several months after receiving the injury may be ; 16 242 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM (1) Complete spastic paralysis in all the muscles below the level of the lesion. (2) The presence of increased reflexes, clonus and Babinski. (3) A complete loss of all types of sensibility up to the level of the lesion. (4) Loss of bladder and rectal control. (5) Normal motoi-, sensory and visceral conditions in the parts of the liody supplied by the segments above the level of the lesion. CHAPTER XIII REMOVAL OF THE BRAIN AND INVESTIGATION OF THE BRAIN-CASE The Cephalic Division of the Central Nervous System. The second of the two major divisions of the central nervous system is the hrain or encephalon. A satisfactory examination of this organ should include not only the study of the brain itself, but also the bony and membranous capsules which contain it. Many important clinical relations exist between the bram and the skull. Their significance cannot be appreciated unless the cranium is studied in conjunction with the encephalon at the time of removal. PRELIMINARY PROCEDURE FOR THE REMOVAL OF THE BRAIX Superficial Incision through the Scalp and Subcutaneous Tissues. A transverse incision is made across the vertex, beginning above one ear and ending above the other. This incision should pass down through the skin, subcutaneous tissue and the aponeurosis of the occipito-frontahs muscle. The cut edge should then be grasped with a piece of muslin or similar material in order to provide a firm grip, and the entire thickness of the tissue covering the cranium will strip readily both forward and backward. The anterior flap should be detached as far forward as the orbital ridges. The posterior flap should be turned back until the greater part of the occipital bone is exposed. Removal of the Calvarium. Incision in the Bone. The head should be placed in the concavity of a block hollowed out for that purpose, and a saw-line for removal of the calvarium should be lightly traced on the skull. This line should start at the midhne anteriorly just above the orbital ridge and be carried outward and slightly downward to end just above the ear on each side. The cadaver should then be turned so that it lies on its face, and a second line traced from the region of the external occipital protuberance for- ward and downward to meet the line alreadj' described just above the ear. This superficial saw cut should then be deepened until the entire thickness of the skull is divided. Care should be exercised that the thin inner table is just cut through. Precaution against injury to the dura and brain is especi- ally necessary at the curve of the forehead, which should not be sawn directly across, but the frontal region should be sawn first and then the saw directed along the lateral aspect of the cranium. The extreme thinness of the cranium in the temporal fossa should be remembered in order to avoid injury to the brain. It may then be ascertained whether the calvarium is free 243 244 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM through its entire circumference, and any remaining pieces of botie can be broken through by means of a chisel and mallet. The calvarium may then be detached. Incision of the Dur.v. The dura should then be incised with a small knife in a cruciform manner, care being exercised not to injure the brain. The dura mater should then be reflected in order to expose to view the underlying structures. Along the great longitudinal fissure, the dura mater will Ijc found to be closely connected with the arachnoid, the pia mater and the hemispheres by means of a numljer of veins which drain the cortex and empty into the superior longitudinal sinus. The Arachnijid and Pia Mater. Careful examination of the convexity of the hemispheres will show the arachnoid stretching over the fissures and convolutions and the pia mater carrying the arteries and veins of the cere- bral circulation. On the surface of the arachnoid will be found granular areas, mainly near the great longitudinal fissure, which represent the Pacchionian granulations or the arachnoidal villi. Along the dorso-mesial border of the hemispheres will be found the torn ends of a number of veins which empty into the superior longitudinal sinus. These veins enter the sinus at an angle directed forward and inward, thus pouring their blood into the sinus against the direction of the stream-flow. Their trunks may be from twelve to fifteen in number. REMOVAL OF THE BRAIN The Anterior Cranial Fossa. In order to remove the brain from the skull, the tips of the frontal lobes should be gently raised. As this is done the orbital plates of the frontal bones and the cribriform plate of the ethmoid bone will become visible. In the center of the cribriform plate of the ethmoid will be seen the crista galli with the falx arising from its caudal margin. On either side of the crista, lying in shallow depressions on the cribriform plate of the ethmoid, will be seen the bulbs of the olfactory tracts, and passing caudally from them the olfactory tracts. The olfactory bulbs should be raised from the cribriform plate, and as this is done a number of very fine nerve fibers will be seen passing from the under surface of the bullis through the foramina in the cribriform plate. These fibers are the Jila olfactoria of the olfactory apparatus. The frontal lobes are then raised further from the orbital plates of the frontal bone, and the free caudal margins of the lesser wings of the sphenoid will make their appearance. The Middle Cranial Fossa. In the midline will l)c seen the dorsal surface of the body of the sphenoid. Just behind the dorsal surface of the body of the sphenoid will be seen two thick nerve trunks located near the midline and directed forward and outward. These are the optic nerres. They are passing to their decussation in the optic chiasm, and enter the skull from the (_irl)its through the optic foramina. The optic nerves are now divided and the brain raised. As a result, two large vessels make their aj)- pearance, one on each side, the internal carotid arteries, which in large part INYESTIGATION OF THE BRAIN-CASE 245 supply the blood destined to the cephalic areas of the brain. The optic chiasm also makes its appearance, and directly behind it will be seen the slender infundibtdar stalk making its way from the under surface of the brain to disappear through a portion of the dura which stretches backward from the posterior edge of the dorsal surface of the bod}' of the sphenoid; this membrane is the diaphragma sellw. Laterally it stretches between the anterior, middle and posterior clinoid processes to form a membrano-osseous pocket in which is lodged the hypophysis cerebri. With the brain raised as far as possible, the point of a sharp knife should be passed through the diaphragma sellse and the pituitary body will he drawn from its resting place, the sella turcica. Immediately behind the pocket in which the pitu- itary body is lodged, and forming the posterior boundary of the sella is a projecting plate of bone, the dorsum sellw, which at its summit presents two tubercles, the posterior clinoid processes. It will now be found that it is not possible to raise the brain further on account of a horizontal partition, the tentorium. cerebeUi, stretched across the posterior portion of the base of the skull and presenting at its center a space through which passes the brain-stem. Incision of the Tentorium. This partition should now be incised at its line of attachment from within outward and backward along the superior border of the petrous portion of the temporal bone. Nerves of the Oculomotor Mechanism. External to and below the base of the dorsum sellae will be found three nerves coursing forward on each side from the brain-stem to disappear by penetrating the dura at the base of the skull; the innermost of these is the 3d cranial nerve {oculomo- torius). Lateral to this nerve is a fine nerve, the 4th cranial nerve [troch- learis), and another small nerve, the 6th cranial nerve {abducens). External to the mesial attachment of the dural partition separating the middle and posterior fossiE is a broad flat nerve penetrating the dura, the 5th cranial nerve {trigeminus), which should be divided close to its point of penetration into the dura. The Posterior Cranial Fossa and Its Nerves. Having divided the fibrous partition attached to the superior border of the petrous portion of the temporal bone, it will be found that the brain can be more freely raised from the base of the skull. As it is raised, two nerves are seen coursing out- ward toward the internal auditory meatus on the postero-superior surface of the petrous portion of the temporal bone. These are the 7th and 8th cranial nerves. They should be divided close to the internal auditory meatus. Further traction on the brain will show a group of three nerves passing outward and shghtly forward from the brain-stem toward the jugular foramen. They are situated almost directly posterior to the internal auditory meatus. These are the 9th {glossopharyngeus), 10th (vagus), and 11th {spinal accessory) cranial nerves. They should be chvided close to the jugular foramen. Mesial to these nerves, and somewhat caudal, will be found the ISth 246 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM cranial nerrc (hypoglossal) passing forward from the brain-stem. This nerve should be divided, and the l^rain may then be removed. If the stem has not been (hvidod at the foramen magnum, a long pair of scissors or a long knife may be passed into the foramen magnum ventral to the stem and the cord separated from the medulla. The brain should be removed gently and the reflection of the dura mater which will be found to lie between the cephalic surface of the cerebellum and the caudal surface of the cerebral Falx Cerebri (Cut Through C)pening3 for the Pasaa^'e of the Nn. Olfactorii V Olfactory Bulb ^=-vi »;:c_.-r! Optic Xei \ f . Internal Carot Artery C'ptic Chiasm ^J Vnt ""i r f ranial Fossa Ml idle Cranial I ossa Cut Margin of the Tentorium Cerebelli Facial and Acous Nerves Glossopharji Nerve r...m Cerebelli Falx Cereb.lli ,' Falx Cerebri (Cut Through) Transverse Sinus Superior Longitudinal Sinus Fig. 219. — Dura mater viewed from above; the falx cerebri lias been almost completely removed, the tentorium cerebelli on the left side only. (Spaltvliuh.) hemispheres may be pulled away from these two structures. The brain should be placed in a jar sufficiently large to receive it without compression, and allowed to rest upon cotton. The jar should contain a 5 per cent solution of formahn. When sufficiently hardened, the brain may be further examined. Certain major divisions may be noted for study. These divisions are: the medulla, the pons Varolii, the cerebellum, the midljrain, the interbrain and the cerebral hemispheres. Each of these parts requires separate description. IN\^ESTIGATION OF THE BRATN-CASE 247 EXAMINATION OF THE DURA MATER COVERING THE BASE OF THE SKULL After the removal of the brain the dura will remain attached to the base of the skull. The cut edge of the dura will be found around the cir- cumference of the bone incision. The dura presents two layers, a tough, firm outer laj^er which is closely adherent to the bones of the skull and forms its periosteum, and a thinner, more delicate inner layer which is in contact with the arachnoid. The space between the dura and the arachnoid is the subdural space. It is in direct continuity with the lymph spaces in the sheaths of the cranial nerves. The subdural space does not communicate with the subarachnoid space. The dura will be found to be continued out- ward on the cranial nerves as they pass to their foramina of exit, where it becomes adherent to them and forms part of their sheath. The dura is more closely adherent to the bones of the skull over the base than over the vertex, especially at the suture lines and over prominences or irregularities of the bones. The space between the skull and the dura is the epidural space. Upper Limit of the Ligamentum Denticulatum. At the foramen mag- num the uppermost part of the ligamentum denticulatum will be found to divide into ventral and dorsal leaves which are applied respectively to the ventral and dorsal portions of the foramen on cither side. The Venous Sinuses. Coursing between the two layers of the dura mater will be found the great venous sinuses of the skull. In the middle fossa there are two such sinuses, the circular and the cavernous sinuses. The cavernous sinuses, two in number, arise at the mesial extremity of the sphenoidal fis- sures by the confluence of the ophthalmic veins, and pass backward in the folds of dura mater which close in laterally the pituitary fossa. The circular sinus is formed by two transverse limbs which pass across cephahcally and caudally around the ohvary eminence and connect the cavernous sinuses. From the foramen spinosum, coursing upward and dividing into an- terior and posterior branches, will be found the -middle meningeal artery, which lies between the laj^ers of the dura mater and supplies a large part of the membrane with nourishment. In the posterior fossa there are a number of sinuses. At the dorsum sells they divide to form two sinuses, the superior and the inferior petrosal sinuses. The superior petrosal sotms runs along the superior border of the petrous-temporal bone and opens laterally into the curve of the .sigmoid sinus. The rnferior petrosal sinus passes backward and downward over the tip of the petrous-temporal bone to the mesial compartment of the jugular foramen, through which it passes. At a point corresponding to the ex- ternal occipital protuberance will be found a depression on the internal surface of the occipital bone which is called the torcular Herophili. At this point the superior longitudinal sinus turns, usually to the right, and becomes the right transrerse or lateral .sinus. As the lateral sinuses pass outward and forward, ihey reach the postero-inferior angles of the parietal bones, where they turn downward, cross the masto-temporal bone, reach the jugular 248 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM processes of the occipital bone, and enter the lateral compartment of the jugular foramen, through which they pass to unite with the inferior petrosal sinuses and form the internal jugular veins. The Reflections of the Dura Mater. The reflections of the dura which form the diaphragma scIUb and the cavernous sinuses have already been described. The tentorium cerebelli is a horizontal membrane dividing the cavity of the posterior fossa into that part occupied by the cerebel- lum which lies below the tentorium, and the part occupied by the cerebral hemispheres which are situated above the tentorium. It is adherent an- teriorly to the superior border of the petrosa, and at its anterior end is attached to the posterior clinoid processes. It is directed somewhat downward, is firm and inelastic. Its circumference is attached to the posterior inferior angles of the parietal bones and to the horizontal limb of the internal occipi- tal crest. At its attachment to the superior border of the temporal bone it contains the superior petrosal sinus, and at its attachment to the parietal and occipital bones it contains the lateral sinuses. In its center it presents a space called the incisura tentorii, which encircles the mesencephalon. The free edges of the incisura are directed forward, cross the attached anterior edge of the tentorium and gain an attachment to the anterior clinoid pro- cesses, the two limljs thus crossing and forming a triangular space through which pass the 3rd, 4th and 6th cranial nerves. Attached to its upper surface and holding it in place and on the stretch is the falx cerebri. The falx is a large membrane located in the sagittal plane and serving to separate the hemispheres. It arises anteriority at the crista galli and continues liackward to end at the superior surface of the tentorium. It is formed superiorly along the entire length of the vertex by a reduplication of the dura which passes downward from the vertex between the hemispheres. Its lower margin is free and lies between the hemispheres. Its vertical height in- creases from before backward, being greatest where it becomes continuous with the tentorium. Along its attached margin is located the superior longi- tudinal sinus which ends at the torcular by turning, in the great majority of cases, to the riglit to liecome the; right lateral simis. Along its inferior free margin is located the inferior longitudinal sinus, which ends by turning along the upper surface of the tentorium to become the straight sinus which turns to the left at the torcular. Another reduplication of the dura is a slight fold which aiises along the inferior hmb of the internal occipital crest and is lodged between the hemispheres of tlie cereliellum. This is the falx cerebelli. It arises below at the foramen magnum, and increasing shghtly in width becomes continuous with the inferior svirface of the tentorium. THE BASE OF THE SKULL WITH DURA MATER REMOVED The base of the skull presents three foss*, an anterior, a middle and a poscerior fossa. The Anterior Fossa. The an.terior /os.sa, is bounded cephalically by the frontal bone and laterally l>y the frontal and parietal bones and the greater INVESTIGATION OF THE BEAIN-CASE 249 wing of the sphenoid. Its floor is formed by the upper surfaces of the orbital plates of the frontal bone and the upper surface of the cribriform plate of the ethmoid bone. Caudally the floor of the anterior fossa is formed by the dorsal surface of the lesser wings of the sphenoid and the dorsal surface of the body of the sphenoid bone. In the midline is placed the crista galli, from the posterior border of which arises the falx cerebri. On either side of the crista galli are the slits for the nasal nerve, by which that branch of the ophthalmic division of the trigeminal nerve leaves the cranial cavity to enter the nasal fossa. Behind and lateral to the slit for the nasal nerve are three rows of foramina, through which pass the fda olfactona from the ol- factory mucous membrane to the olfactory bulb. The caudal limit of the anterior fossa is formed by the free edge of the lesser wings of the sphenoid and the caudal edge of the dorsal surface of the body of the sphenoid. The Middle Fossa. The middle fossa is much more spacious than the anterior. It is deep laterally and hollowed out to receive the tips of the tem- poral lobes. It is somewhat in the form of a butterfly, and is limited cephalically by the free caudal margins of the lesser wings of the sphenoid, the caudal border of the dorsal surface of the body of the sphenoid bone, and the frontal bone. Caudally it is limited by the superior border of the petrous portion of the temporal bone. Laterally it is bounded by the anterior inferior angle of the parietal bone, the squamous portion of the temporal bone, the greater wing of the sphenoid and the posterior inferior angle of the parietal borfe. The floor is formed by the greater wing of the sphenoid and the squamous and petrous portions of the temporal bone. Mesially the floor is raised above the level of the lateral portions of the fossa and is formed by the body of the sphenoid bone where the pituitary fossa is found. The caudal limit of the middle portion of the fossa is formed by the dorsum sellae, which rises from the body of the sphenoid and presents at its summit two processes which diverge laterally, the posterior clinoid processes. The free margins of the lesser wings of the sphenoid are prolonged backward mesially to form two free processes, the anterior clinoid processes. Below the free margins of the lesser wings of the sphenoid is the sphenoidal fissure or the anterior lacerated foramen, through which pass the 3rd, 4th and 6th cranial nerves, the ophthalmic division of the 5th nerve, the orbital artery, the cavernous plexus of the sympathetic and the ophthalmic veins. Mesial to the base of the sphenoidal fissure, and separated from it by one of the pillars of the lesser wings of the sphenoid, is located the optic foramen, which crans- mits the optic nerve and the ophthalmic artery. The pituitary fossa is formed by the dorsal surface of the body of the sphenoid below and cephalic- all}'; laterally it is closed in by folds of dura mater which pass between the anterior middle and posterior clinoid processes ; these folds of dura mater en- close the cavernous sinuses and the nerves which enter the sphenoidal fis- sure. The caudal limit of the pituitary fossa is formed by the dorsum sella;. The roof is formed by a reflection of the dura called the diaphragma sella', which is pierced near its center by the stalk of the pituitary gland. Emerging from the dorsal border of the cavernous sinus and severed in the 250 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM INVESTIGATION OF THE BRAIN-CASE 251 removal of the brain, will be found the stumps of the internal carotid arteries. The cephahc part of the median portion of the middle fossa is occupied by the optic chiasm which Hes in front of a bony protuberance, the olivary eminence, which at its lateral limits presents the middle clinoid processes. The anterior and middle clinoid processes may unite to form a bony canal through which passes the internal carotid artery. To the caudal edge of the olivary eminence is attached the cephalic margin of thediaphragmasellaj. Below and lateral to the root of the dorsum sella is located the foramen lacerum m.edium which is filled in the recent state by cartilage. Through this cartilage pass the internal carotid artery and the Vidian nerve, which is made up by the great superficial and the great deep petrosal nerves. In front and to the outer side of this foramen is located the foramen ovale, through which pass the m.andihidar division of the 5th nerve and the small meningeal arterij. Lateral to the foramen ovale is the foramen spinosum, which transmits the middle meningeal artery. Cephalad and mesial to the foramen ovale is the foramen rotundum, which transmits the maxillary division of the 5th nerve. The middle fossa is crossed by the spheno-parietal, the squamo-parietal, the squamo-sphenoidal and the petro-sphonoidal sutures. On the summit of the superior border of the petrous-temporal bone close to the base of the posterior clinoid processes will be found a notch through which pass forward from the brain-stem the 3rd, 4th and 6th cranial nerves to enter the wall of the cavernous sinus. External to this notch is a shallow groove for the dorsal root of the 5th nerve. The dorsal root of the 5th nerve, as it penetrates the dura mater, enters a pocket between the two layers of the dura mater, the cavum Mecklii, in wdiich is lodged the Gasserian ganglion. This ganglion lies on the tip of the petrosa of the temporal bone, and from it arise the three sensory roots of the 5th cranial nerve. Closely applied to the ganglion is the motor root of the 5th nerve. Passing dorsally and mesi- ally from the ganglion is the ophthalmic division of the 5th nerve on its course forward and upward to enter the external wall of the cavernous sinus. Coursing almost directly forward to the foramen rotundum is the maxillary division, and passing outward and downward to the foramen ovale is the mandibular division of the 5th nerve. The Posterior Fossa. The posterior fossa is hmited cephalically by the dorsum sellae, and the superior border of the petrous-temporal bone. Later- ally and caudally it is limited by the mastoid portion of the temporal bone and the occipital bone. The floor is formed by the occipital bone, the basi- occipital and the basi-sphenoid. The posterior fossa is larger and deeper than the others and lodges the medulla, pons and the cerebellum. In the center of the fossa is the foramen magnum, which transmits the neuraxis, the vertebral arteries and the spinal root of the spinal accessory nerve. On the postero-superior surface of the petrous-temporal bone is the internal auditory meatus which transmits the 7th and Sth cranial nerves, and between them the pars intermedia of Wri.sberg which is the sensory root of the 7th cranial nerve. Below and behind the internal auditory meatus is the posterior 252 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM lacerated foramen or ihe jugular foramen, which transmits the 9th, 10th and 11th cranial nerves and the inferior petrosal and lateral sinuses. This fora- men is divided into three compartments by two processes of the dura mater: the mesial compartment transmits the inferior petrosal sinus, the lateral compartment, the lateral sinus, and the middle compartment transmits the three nerves and a small meningeal branch from the ascending pharyngeal or occipital arteries. Just above the edge of the foramen magnum, lateral to its midpoint, will be found the anterior condyloid foratnina , which are directed cephalically and laterally and transmit the 12th cranial nerves. These foramina are also called the canales hypoglossi. CHAPTER XIV THE MEDULLA OBLONGATA ENCEPHALIZATION AND A GENERAL VIEW OF THE MEDULLA The Prolongation of the Spinal Cord into the Head. The portion of the neuraxis protected by the vertebral column is the spinal cord or myelon, while the portion to which tlie skull gives protection is the brain or encepha- lon. The transition from vertebral cokmm to skull is marked topographically by the upper border of the atlas. That portion of the neuraxes above this border and within the skull is the brain. In passing from vertebral column to skull there are manj- striking differences in form and appearance, which depend upon the development of the head. Similar differences are observed in passing from the spinal cord to the brain. These latter changes, however, are more gradual. The caudalmosfc portion of the brain has, therefore, much in common with the general appearance of the spinal cord. It is for this reason often called the "prolongation of the spinal cord," but more usually is referred to as the medulla oblongata. This part of the brain is also known as the myeUncephalon, thereby denoting the region of transition in the neuraxis which presents features common to both myelon and encephalon. The medulla oblongata, studied as a division of the human central nervous system, has proved a structure difficult to understand. Its organiza- tion seems to differ much from that of the spinal cord. Yet the funda- mentals of the neuraxis seen in the spinal cord are also to be found in the medulla oblongata. They have become modified and supplemented in many ways. When, however, the reasons underlying these modifications are ap- preciated, the significance of the medulla is easily understood. The myelen- cephalon, like the myelon, is a segmented structure. But being a segmental portion of the neuraxis, why have its segments become so profoundly altered? This question leads back into the ancient history of the verte- brates. It is involved in the record of those advances in animal life which have eventuated in the development of the head. Influences Determining the Formation of the Head. Long before the age of vertebrates, influences which determined the foimation of the head were at work. The oldest part of the head is the mouth ; its chief primitive activity was the capture and introduction of food into the body. Even anemones and corals have well-defined mouths surrounded by sensory tentacles which aid in procuring food. The mouth, of necessity, became the point of approach which guided the animal to food supply. It thus de- termined the direction of locomotion, and in this manner laid the foundation for the extensive superstructure ultimately developed at the cephalic ex- tremity of the animal. This process which resulted in the formation of the 2.53 254 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM ■y 't H Hi fi I Fi. head is known as oncephalization. It received its initial impetus through the effects of direct- ing animal motion, and rapidly began to ex- pand its field of influence by the accession of oi-gans whose purpose was the more effectual guidance of locomotion. The addition to the head of primitive visual organs, such as those seen in the flat wonns, was a distinct gain in directing motion. The concentration of certain nervous elements to foini primitive gustatory and olfactorj- ap- paratus, as well as highly specialized tactile organs, the tentacles, brought new accretions iif power to the cephalic region. The head be- came the chief guide of action in the lower forms, in which it foreshadowed the ultimate dominant control of the brain over the ac- tivities of the higher animals. Influences Producing Modifications in the Head. Food supply in the primitive race for life is never a gratuity, and no principle has Ijeen more availing to secure existence and stimulate progress than the law of might. The head, therefore, developed as an efficient in- strument of attack, and was at the same time well provided for the defense of the delicate organs which it contained. The mouth came to be surrounded Ijy bony jaws ecjuipped with teeth, and the head was incased in a tough skin or covered with armor-like scales for protection. The vertebrates in their beginning showed this specialization for offense and defense in a high degree. Certain ancient fish-like animals of the Silurian and Devonian ages had a head covered by bon}^ skin which served as a helmet. Among the lower vertebrates, the sharks present all of the familiar features of the head, including the mouth surrounded by jaws which have a formidable ecpupment of teeth, the tongue and the lips, the nostrils and the well protected eye-balls. How much these advant- ages of the animal's head have added to the 221. — Dissection shouing the spiiiiil cord and some of the prominent changes in passing upward into the brain, especially in the "prolongation of the spinal cord," the medulla oblongata.. [Boargcnj.) J \m m m 'A' THE MEDULLA OBLONGATA 9P, 00 Fig. 222. — Dissection showing some of the conspicuous differences in passing from the vertebral column to the skull. The marked differences between the spinal cord and brain are also seen. iBourgery.) 256 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM effectiveness of seeking and capturing its prey, as well as providing defense against its natural enemies, is obvious at a glance. The Requirements of Respiraiion — The Gills. As distance receptors, the eyes, taste-buds and olfactory organs serve as the essential directors of motion, both in pursuit and flight. In the fish, however, the head ha.s as- sumed several other responsibilities. One of these activities is connected with the mouth. Primarily serving for the intake of food, the mouth also N. 1. 1, \D Lobus lina; lateralis — TabercuJum acousticum ^ Fasc. long, med Lobus viseeralis Fig. 223. — The medulla oblongata and cerebellum of the lake sturgeon {acipenser Tubicundus) to show the longitudinal columns which have been differentiated in correlation with the peripheral functional systems. ,4 13 a dorsal view with tlie rnenibranou3 roof of the fourth ventricle removed to show the longitudina columns within the ventricle. B. C. and D arc sketches of cross sections at the levels indicated in which the four functional columns are diagramniatically shaded, the somatic motor by white circles, the visceral motor by white rectangles, the visceral sensory by oblique cross-hatching, and the somatic sensory by vertical cross-hatching. The Roman numerals refer to the cranial nerves. {From Johnston's is'ervous System of Verlebmles.) became implicated in the function of respiration. This new function was intimatelj' associated with the development of certain aerating organs, the gills. These structures consist of a set of vascular fringes situated upon either side of the head in connection with the mouth cavity. Their arrange- ment permits the water to circulate freely about the vascular fringes which constitute an aerating apparatus. In this manner, oxygen is taken up by the blood from the water. The gill apparatus, in addition to this provision which THE MEDULLA OBLONGATA 257 it makes for the respiratory necessities of the animal, presents pecuharities in form which are equally notable. Like the body segments, the gills are arranged as a series of similar structures which vary in number from five to seven and consist of gill arches with gill clefts between them. Appended to each arch is a highly vascular gill fringe. This regular series of structures in the head region, serving the purposes of respiration, is derived from the branchiomeres or gill segments. They differ in respect to their origin from the bodj' segments, which arise from the metameres. In the same manner that the metameres have made a deep impress upon the spinal cord, so the seg- ments which developed in the head region in relation to the gill arches have made a correspondingly deep im- print upon the medulla oblongata. Encephalomeres and Myelomeres. It is not surprising that the type of segmentation should differ in the spinal cord and the brain-stem. McClure has made a nominal distinction between these typos by terming the segments of the spinal cord myelomeres and those of the brain-stem encephalomeres. The ex- planation of the chief differences between these two varieties of neural segments is found in the two types of segmentation which impress them- selves upon the central axis. The melameres (body segments) are a re- gular succession of equivalent segments in the region of the spinal cord. The wholly different and yet meristic series of branchiomeres (gill segments) is dominant in determining the form of the medulla oblongata. The major segmental influence upon the brain-stem is derived from branchiomeric segmentation. The effects of metameric segmentation, although over- shadowed by the gill arches, may be discerned to some extent in the medulla. While the encephalomeres are a series of equivalent structures, they do not present any exact equivalency with the myelomeres. The encephalomere, in the medulla at least, is morphologically and physiologically different from the myelomere. It takes its chief importance from the role it plays m control of the gill apparatus. Its function is most intimately connected with the regulation of respiration and is, therefore, essentially splanchmc. The functions of the myelomeres are more especially somatic. 17 Fig. 224. — Diagrammatic representation of the myel- encephalon (medulla) in the vertebrate series. Ventral view. Pctromyzon (lamprey) above. Scyllium canicula ^dog-fish) below. 258 FORM AND FUNCTIONS OP THE CENTRAL NERVOUS SYSTEM Control of the Medulla Over Respiration, Cardiac Action and Gastro- intestinal Activity. From the association of the gill mechanism with the process of aeration of the blood, it may be assumed that the chief organ of circulation would be situated in close relation with these arches. It is for this reason that in all of the fish, and in all animals depending upon gills for the aeration of the blood, the heart is situated in close proximity to the gills themselves. The distinct autonomy of the myelomere over its corre- sponding body segment has already been discussed. It has been seen that the principal office of such a segment of the nervous sj^stem is the control of somatic activitJ^ The major control of the encephalomere, particularly in the region of the medulla oblongata, is concerned in the regulation of those receptors and effectors which cooperate in the process of aeration of the blood. This is a visceral or splanchnic activity. The encephalomeres of the medulla oblongata control the activity of the heart in relation to aeration of the blood and general systemic circula- tion. The influence of this early responsibility of the medulla in regulating respiration and controlling cir- culation has been transmitted through the entire line of vertebrates. It is present in those forms which came after lungs had replaced gills and the aquatic mode of life had yielded in favor of air breathing and other terrestrial habits. The primitive relations of the mouth as an aperture for the intake of food and for aerating the blood have determined a close association between the cardio-vas- brain cular, alimentary and respiratory systems. This rela- of the catfish as seen tionship is reflected in the influence which the medulla from above. (Hcr/'icA.) oblongata has continued to exert over these three ^a— tubercuium acoust- systcms. The coutrol of deglutition and gastro-intestinal icum; U>h. vao — lobi vagi; ... . . . cbi — cerebellum; op. I— activitics, rcspu'ation and cardiac action, has come to optic lobes; c6 — cerebrum. , i 1 • j.1 i ii i 1 x be an autonomy vested m the medulla oblongata. From this fact the organ takes its chief importance in the regulation of life, and has gained its reputation as the " neud vital" (vital node). The Necessary Increase of Gray Matter in the Medulla. The require- ments for the regulating of these vital processes have imposed upon the medulla certain modifications of form for which there are no ana- logues in the spinal cord. Because it is a portion of the nervous system which holds such autonomous control, it has, of necessity, developed more particularly along the line of its gray matter, the active substance. The result of this development is seen in the enlargement of the medulla ob- longata as a whole when compared with the spinal cord. It is further evi- denced by the appearance of the fourth ventricle, which has permitted the expansion of the central gray matter. The fourth ventricle is a chamber re- sulting from the failure of fusion of the two alar laminse. The central gray matter in this way acquires greater proportions than in the spinal cord. THE MEDULLA OBLONGATA 259 In some of the fish, this ventricle is not only an extensive cavity but also presents upon its floor a series of longitudinal columns or lobes of gray matter. The most prominent of these lobes is the lobus visceralis, which controls respiration and cardiac activity. It also has a gustatory function. The lobus linew lateralis and the lobus somaticus act in the direction of motion and the regulation of body balance. The Development of the Fourth Ventricle. The primitive central canal of the spinal cord is entirely surrounded by gray matter. In the medulla it becomes dilated to form the fourth ventricle. In the earliest phase of development, the central nervous system presents itself as a slightly differ- entiated neural plate. Subsequently the neural groove is formed by the Inner layer Roof plate Tractus solitarius Formatio reticularis gn ea Formatio reticularis alba N. XII Spinal V Neuroblabtb Ir jm alar plate Marginal lai er Neuroblasts from alar plate (Rudiment of accessory olive) Fig. 220. — Transverse section through the medulla of an eight-weeks human embryo. (His.) appearance of the two neural folds. These folds rising gradually, ultimately fuse in the mid-dorsal line, thus giving rise to the neural tube which encloses a large central cavity, the neural canal. This canal is surrounded by the central gray matter. As development proceeds, the gray matter in the spinal cord is enveloped by a medullary velum consisting of neuraxones, the beginning of the white matter. In the medulla, however, there is no disposi- tion on the part of the mcidullary substance to envelop the central gray matter. The extreme development of the central gray matter seems to preclude such envelopment by white substance. For this reason the central canal re- mains open and thus facilitates the expansion of the central gray svibstance. The Development of the Gustatory Sense. The medulla oblongata, through another important function, serves to increase the animal's effi- ciency in the search and collection of food. This object is accomplished by the aid of the gustatory or taste sense. In man 3^ fish, taste-buds are dis- tributed throughout the mouth and along the gills and head. Some of the bony fish are still more extensively equipped with these organs, which are richly distributed over the fins and body. 260 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM The Development of the EquUibratory Mechanism. In addition to this visceral reKulation, the medulla oblongata has assumed certain functions concerned in maintaining the balance of the l:)odj'. These balancing activi- ties, particularly in aquatic animals, are constantly in demand. The case is different with terrestrial animals, whose requirements in balancing are more transitory and ii'regular. The fish, because of its continuous needs in equilibrium, requires a more extensive mechanism for this purpose. It lives in a fluid medium and must constantly maintain its body in a certain posi- tion. No such iminterrupted demand is made upon terrestrial animals. Their medium is not only more stable, but also furnishes firm support for the body. In the fish, pro vision for a balancing apparatus is made in two special sets of organs whose central control is vested in the medulla oblon- gata. The first set consists of a series of semicircular canals situated in the head. These canals are so arranged as to act as water levels for the three planes of space. The semicircular canals seem to regulate dynamic equilibrium while the animal is in motion. Ancillary portions of this ap- paratus, the utricle and saccule, serve the purposes of Fig. 227. — DiaKi'ainiiiatic representation of the niyel- encephalon (medulla) m the vertebrate series, static equilibrium, while the Ventral view. Salrno salar Isalnntii) above Rana esculonta ffrog) below. annual is at rest. The second set of struc- tures in the balancing mechanism comprises th« lateral line organs or the neuromast system. This system consists of a collection of specialized receptors situated upon the head in supra-orbital, infra-orliital and hyomandibular rows. It is also arranged in a line along the sides of the body extending from the head to the tail, and occupying a position midway between the dorsal and ventral fins. These two sets of balancing organs provide for the static and dynamic equilibrium of the body. They furnish a balancing mechanism governing the movements of locomotion and rest. The Development of Special Organs of Offense. A further tendency for specialization in the medulla oblongata is seen in the electric lobe which develops in certain fish. This electric organ consists of a large collec- tion of nerve cells connected with specialized effectors upon the surface of the body. The electric lobe serves the animal in overcoming its quarry. It generates an electric force sufficient to stun or momentarily to paralyze THE MEDULLA OBLONGATA 261 its prey. Such an organ is found in the medulla of one of the Selachians, the torpedo. The Primitive Functions of the Medulla. The primitive function of the medulla oblongata is the control of those visceral activities necessary to maintain life. The manner in which the medulla came to be the dominant regulator of respiration, cardiac action, deglutition and digestion, seems clear. All of these functions are closely related and their organs intimately connected. The proximity of the gills to the heart, of the mouth to the pharynx and stomach, bespeaks a close functional association indicative of the autonomy in the medulla which dominates the vital processes. These functions have been supplemented by others which made possible the most precise direction of body movements, and in some instances have provided a mechanism, such as the electric organ, to facili- tate the capture of prey. Modifications due to the Assumption of Terres- trial Life. Air Breathing. During the critical epoch when vertebrate development led to the tran- sition from acjuatic life to terrestrial habitat, a de- cisive change in environment produced far-reaching effects upon all parts of the body. These changes have been especially reflected in the medulla oblon- gata. Air instead of water now served as the medium to bring oxygen to the blood and the type of re- spiration was profoundly altered. The mechanism of the gills, which provided for respiration in water, was no longer adequate to the demands of air breathing. After manj^ progressive modifications the structures necessary for the development of the pulmonic S3'stem finally made their appearance. In producing these changes, what was old has been made use of in the new. The central nervous system in particular has adhered to its ancient hues. In the terrestrial animal the medulla oblongata still preserves its regulating influence over the new order of respiratory mechanism. It also main- tains its dominant control of cardiac functions and gastro-intestinal action. RECE.SSION OF THE Taste-Buds AND LATERAL LiNE Organs. The dis- appearance of the taste-buds from the head, from the gill arches and from the surface of the body decreased the importance of the lobus viscerahs, which became reduced in size. Upon the assumption of terrestrial habits, the lateral line organs ceased to be of service, since the medium on which they depended no longer surrounded the body. This change eventually led to the disappearance of the lateral line system, which, however, was replaced by a new set of receptors sensitive to the stimuli of sound. By gradual transi- tion the open pit canal organ of the lateral hne came to be differentiated as Fig. 228.— Brain of the carp as seen from above. {HerricI:.) Lob. vag — lobi vagi; cbl — cerebellum; op. I — optic lobes ; ff> — cerebrum. 2(.i2 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM the ear, which furnislied if not a wholly new sense mechanism, one at least profoundly modified and susceptible to the stimuli of rapid air waves. The vestibular mechanism, in consequence of this modification, received a new element in air-breathing animals. The ear eventually assumed a dual func- tion, i.e., the ancient one handed down from ac|uatic life and dependent upon the semicircular canals, the utricle and saccule; and a second function probably arising out of the highly modified lateral line system which gave rise to the cochlea and made possil)le the sense of hearing. Phoxation and the Dp:\'elopme\t of the LarYx\t:. It is probable that no circumstance in tht; evolutional process reveals more directly the results of cause and cFIcct than the development of phonation in response Fig. 229. — Diagraimuatic ropresentation (jf the iriyelencophalun (medulla) in the verte- Vjrate series. Ventral view. Alligatiir niississippiensis (alligator) abo^-c Coluinba ipignju) below. to the appearance of the organ of hearing. The auditory sense provided the animal with new information regarding its environment. It also made pos- sible a means of communication which much increased the range of herd activities and ultimately enriched racial experience by the addition of one of the most effective instruments in social relations, the voice. Without the sense of hearing, the voice would have no reason for being. This is well shown in those born deaf, for in deaf mutes the development of the voice is either negligible or abnormal. At the time whsn the lungs first made tlioir appearance, they developed as an ofl'shoot from the gastro-intostinal canal. Because of this relation, food and air have a commcm passageway for some distance from the mouth. At a certain point, however, a critical selection became necessary whereby the food should follow its own course and the air enter passages especiaUy THE MEDULLA OBLONGATA 263 designed for it. There could be no intermingling of these two elements, the food and the air, at this critical point. In response to this need, a sensitive mechanism composed of a set of delicate valves was established at the junc- tion of the food and air canals. The lungs especially required protection against the entrance of food, and out of this need arose the glottis, the epiglottis, and the larynx with its highly specialized vocal cords. The intimate relation between the lungs and the gastro-intestinal tract accounts for the control which the medulla has over both systems. It is but a natural consequence that this part of the brain should also regulate the mechanism which has guarded the entry into the lung and eventually developed into the organ of voice. The D evelopment of the Mobile Head and Tongue. Another decisive change came with the appearance of the neck and the development of the mobile head. This mr)di- fication was determined in the interest of greater range in directing movements of the body and extremities. The in- creased mobility complicated the function of balance. It in- troduced new planes of motion between the head and the trunk and created new de- mands upon the balancing mechanism. It also added much to the function of equih- brium as concerned with move- ments of the eyes and the head p,,. 230.-Diagrammatic representation of the myel- together. encephalon (medulla) in the vertebrate series. The addition of the mobile, Ventral view, muscular tongue imphcated '^'"P"' '■"'^^'^' "''°^'=- "^""'^ famiiians ^dog) beiow. the medulla in another function and complicated its branchiomeric control by the inclusion of the myotomes of two or three body segments (lingual meta- meres). In this light, the segmentation of the medulla, at least in the higher vertebrates, must be complex. It is fundamentally influenced by the gill segments, but is later supplemented by the addition of at least two or three metameric segments. The encephalomere of the medulla is not, therefore, the equivalent of the mj^elomere. In the higher vertebrates it represents a branchial segmentation to which is added an element of metameric segmentation. Modifications of the Face. Certain changes in the face also made their impress upon the medulla oblongata and determined the development of one of its most prominent nuclei. The face in the lower terrestrial verte- 264 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM brates consists of a bony mask covered l)y skin, quite incapable of facial movements and devoid of facial expression. When the scaly skin is removed from the facial portion of the skull in the reptile, no facial muscles are found. This immobile and non-muscular face also occurs in birds. It is only in the mammals that the soft muscular lips and the muscular layers about the nose, eyes, ears and forehead make their appearance. Ecjuipped with this facial musculature capable of expressing variou.s emotions, the mammal has acquired a new instrument for adjustment to its social environment. The expression of anger serves as a warning of encroachment, as that of hatred is a warning of impending attack. These and many other emo- tive expressions furnish an efl'ective equipment for social adjustments possessed only hiy such animals as have a muscular, mobile face. The origin of the facial muscles is a matter of dispute. It seems probable that the facial nerve supplying these muscles had its inception in the nerve fibers which originally supplied the platysma muscles on the surface of the throat, as well as the immediately underlying sphincter colli muscle. This sheaf of subcutaneous muscle has gradually shifted upward to take its place over the old bony mask of the vertebrate head beneath the skin. It has carried with it the original innervation through the facial nerve. It seems probable that these ])rimitive muscles, situated in the region of the neck and ultimately spreading to the face, arose as part of the gill apparatus. They would in this sense be derivatives of the gill muscles which were supplied by the post-trematic branch of the 7th nerve in the fish. The Influence of Suprasegmental Structures. Among the other mfluences modifying the form of the medulla must be nrentioned the greater need for equilibratory control witnessed in the development of the cere- bellum, and the introduction of volitional control attending the appearance and expansion of the cerebral hemispheres. The medulla oblongata, from the beginning of vertebrate organization, has comprised a series of segments in which was vested the autonomous control of cardio vascular, respiratory and gastro-intestinal activities. To these offices have been added the regulation of body movement in the in- terests of equilibrium and a special mechanism which made the auditory function possible. The interpretation of the anatomy of the medulla will be aided by hold- ing these facts in the foreground. The explanation of the modifications to which this organ has been sul)ject in man nmst be sought in the progressive adaptations developed in consequence of special adjustments to terrestrial life. CHAPTER XV THE MEDULLA OBLONGATA RELATIONS, SURFACE APPEARANCE AND ANATOMY OF THE MEDULLA Situation, Boundaries and Relations. The medulla oblongata is situated within the cranium and forms the caudalmost portion of the brain. Upon removing the brain from the skull, the lower portion of the medulla ob- longata is found engaging the foramen magnum. The caudal boundary of the medulla is indicated by a plane passed horizontally through the lower margin of the foramen magnum, or, accord- ing to some authorities, the upper border of the atlas. The transition from spinal cord to medulla oblongata is not well defined. Indications of it may be found upon the neuraxis by distinguishing between the lowermost root fibers of the hypoglossal nerve and the most cephalic fibers of the first cervical nerve. A plane passed horizontally through the interval between these nerve fasciculi determines the lower boundary of the medulla. Another means of distinguishing this plane of transition is affprded by the lowest fasciculus of the pyramidal decussation. This line of demarcation, however, is not reliable. It is subject to much variation, since the lowest fibers of the pyramidal decussation are often obscured from view. The upper boundary of the medulla, upon its ventral aspect, is the bulbo- pontile sulciis. The boundary line upon the dorsal aspect is indicated by the position of the striae acousticae. This boundary, however, being subject to much variation, is not reliable. The medulla occupies the basilar groove of the basi-occipital portion of the occipital bone. Interposed between the bone and the ventral surface of the medulla are the dm-a mater and the ventral e.xtension of the cisterna magna. The dorsal surface of the medulla is in relation with the vallecula of the cerebellum; while its lateral surfaces are in apposition with the ventral extension of the cerebellar hemispheres. Dimensions and Coverings of the Medulla. The medulla is about 20-24 mm. in length. Its diameters at its caudal extremity are : transverse, 12 mm.; ventro-dorsal, 9 mm. From this level its enlargement is slow at first, but ultimately, as it approaches its cephalic extremity, it begins to increase rapidly in its diameters. At the plane of the bulbo-pontile sulcus its transverse diameter is IS mm. and its ventro-dorsal diameter, 15 mm. The coverings of the medulla consist of (1) an inner vascular membrane, the pia mater, (2) an intermediate membrane, the arachnoid ; (3) the cerebro- spinal fluid contained in the subarachnoid space; (4) an outer membranous covering, the dura mater, and (5) the bony portion of the skull formed by 26.5 266 FORM AND FUNX'TIONS OF THE CENTRAL NERVOUS SYSTEM the basi-occipital, exoccipital and supra-occipital segments of the occipital bone. PiA ^NIater. The pia mater of the medulla oblongata presents certain peculiarities. In addition to the fact that it is a closely investing vascular membrane, it also forms the tela chorioidea inferior. This is a combination of the ependymal layer, forming the roof of the fourth ventricle, and the pia mater. Situated above a portion of this ventricle, the roof membrane and the pia make numerous invaginations which give rise to the chorioid fdexus. This structure is also known as the chorioid gland. It is active in the secretion of the cerebrospinal fluid. IMost of the chorioideal invaginations occur in the immediate vicinity of the midline, where they appear as parallel, fringe-like projections. They form a median plexus which extends upward from the region of the obex to the inferior medullary velum. At the beginning of the lateral recesses, the plexus diverges in both directions laterally and gives rise to the lateral plexus which fills the lateral recesses. This portion of the chorioid glantl system of the fourth ventricle extends along the lateral aspect of the medulla oblongata in relation with the ninth and tenth nerves, and projects into the subarachnoid space upon either side. ApEHTfREs OF THE FouRTH VENTRICLE. In early fetal life, the tela chorioidea is impervious. At about the fifth or sixth fetal month, it is perforated to form a median opening known as the foramen of Magendie or aperiura medialis ventricidi quarti. This foramen lies immediatelj^ above the obex and between the strands of the chorioid plexus. Two other openings through the chorioid plexus appear in connection with the lateral recesses and are known as the foramina of Luschka (aperturse laterales). These two aperoures are usually present, one on either side, in the wall of the lateral recess, close to the vagus and glossopharyngeus nerves. The three openings in the tela chorioidea afl'ord communication between the ventricular system and the subarachnoid space. The cei'ebrospinal fluid secreted b3' the chor- ioidal glands of the lateral, third and fourth ventricles has, by this provision, a means of constant drainage, which prevents the distension of the cavities of the brain Ijy the accumulation of cerebrospinal fluid. Arachnoid and Subarachnoid Space. The covering of the medulla immediately external to the pia mater is fluid — the cerebrospinal fluid contained m a special division of the subarachnoid space. This particular division of the subarachnoid space constitutes the cisterna magna {cisterna cerebello-medullaris). It is in relation with the dorsal surface of the medulla and continuous, through the foramen magnum, with the dorsal portion of the subarachnoid space of the spinal cord. The arachnoid passes from the dorsal aspect of the cerebellum to the dorsal surface of the medulla. The upper part of the medulla is thus com- pletely invested by the subarachnoid cavity. Dura Mater. The dura mater, hning the skull, differs from that of the spinal cord in the following particulars : 1. It is closely adherent to the bone and serves as a vascular membrane for the nutrition of the bony tissue. THE MEDULLA OBLONGATA 267 2. It is continuous with the external periosteum of the cranial bones through the large foramina. 3. It reproduces itself in a number of important processes and partitions. 4. It forms certain large channels for the conveyance of venous blood. Caudate Nurlous Lenticular Nui'leus Corona Radiata Tail of Tau date Nucleus Optic Chiasm Tuber Cinereum Corpora Mam Internal Capsule Vagus, Glossopharyngeus Spinal Accessory Ner\ ps Hypoglossal Ner\f Inferior ( )li\ i Bulbo-Pontile Sul' u' Ventro-Ijatera] Sulcus Trigeminal Portio .Major J ^erve Basilar Groove Pons A.uditory Nerve Fai;ial Nerve bT ludil Fiber; \bdurpns NpFve H\pog]ossal Nerve P\raniid ^ entro-Mpdian Sulcus 1 yraniidal Decussation Spinal Aressory Nerve —Lj % "^ ^ -vj Sulcus Intermedius - , | i )i« w^iF' — ^ Spinal Accessorv Nerve f^ « '^ 3 i Fn_i. 23L — Ventral view of the neunixis with the left internal capsule exposed. Arteries of the Medulla Oblongata. The arterial supply of the medulla oblongata is derived from the anterior spinal, the vertebral, the basilar, and the posterior inferior cerebellar arteries. The medullary arteries are of two types. The first type consists of the median vessels which enter the medulla by means of the ventro-median fissure and come into immediate relation with the raphe to supply the central gray matter and adjacent nuclei. The second type consists of the radicular vessels which enter the 268 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM medulla in connection with the nerve roots. Upon coming into contact with the medulla, the i-adicular vessels break up into two branches, (1) a periph- eral branch which follows the course of the nerve, and (2) a central branch which makes its way toward the various nuclei in the gray matter and to the fasciculi of the white suljstance. Median branches of the anterior spinal arteries supply the nucleus of the h3'poglossal nerve and the bulbar portion of the nucleus of the spinal accessory nerve. Radicular Ijranches from the vertebral arteries at their point of junction to form the basilar artery, suppl,y the nuclei of the vagus, the glossopharyn- geus and both divisions of the acoustic nerve. Radicular branches of the basilar artery supply the nucleus facialis and the motor and sensory nuclei of the nervus trigeminus. The lateral circumference of the medulla and chorioidal plexus are supplied by branches of the posterior inferior cerebellar arteries. External Markings and Surface Features of the Medulla Oblongata. To appreciate the significance of the transition from spinal cord to medulla, it is convenient to consider certain changes observed upon each of the three aspects of the neuraxis, that is, (1) the ventral, (2) the lateral, and (.3j the dorsal surface. Tr.\nsitiox from the Spinal Cord to the ^Medulla as Seexvpox THE Vextr.\l Surface. The first difference seen upon this surface in pass- ing from spinal cord to medulla is the gradual increase in the transverse diameter. This diameter is 9 mm. at the upper cervical region of the cord and 18 mm. at the bulbo-pontile sulcus. This increase in diameter is indicat- ive of large accretions in nerve substance, particularly in the amount of gray matter. The chief features upon the ventral siu-face of the upper cervical seg- ments of the spinal cord are : 1. The vcntro-median sulcus, into which the pia mater dips to carry with it branches of the anterior spinal artery. 2. The ventro-lateral sulcus, which marks the point of emergence of the ventral root fibers. .3. The fairly well-defined ventro-paramcdian sulcus, lietween the ventro- median and the ventro-lateral sulci. Pyramidal Decussation. In the medulla the ventral surface presents two fairly tlistinct divisions, a cephalic pyramidal portion and a caudal infrapyramidal portion. Immediately after passing from the upper levels of the cord into the medulla, the first change noted is the disappearance of the ventro-median fissures. This is due to the fact that a number of inter- lacing and crossing bundles of fibers appear at this level and indicate the position of the decussating pyramidal tract. It is here that the fibers which arise in the motor cortex of the cerebral hemispheres make a more or less complete crossing, so that the right side of the lirain may send impulses to the left side of the body, and vice versa. Approximately 80 or 90 per cent of the pyramidal fibers, decussate at THE MEDULLA OBLONGATA >69 this level to form the crossed pyramidal trad. The fibers which do not cross constitute the direct prtjamidal tract or fasciculus of Tiirck. In rare instances, all of the fibers of the pyramidal tract make a complete decussation at this level, thus suppressing the direct pj^ramidal tract altogether. This arrange- ment is observed in many of the lower animals. On the other hand, the direct pyramidal tract, because of a scant decussation in the crossed pyramidal fibers, may appropriate as much as 90 per cent of the cortico-spinal tract. In this case the ventro-median sulcus remains a prominent feature of the ventral surface of the medulla oblongata. Usually the pyramidal decus- sation is symmetrical, and about an equal number of fibers cross from one side to the other. Asymmetries, however, are occasionally observed; these are due to an inequahty in the pyramidal decussation. The decussating fibers foUow a regular order in their crossing. Those fibers destined to supply the cord segments for the fingers, hand, forearm and arm, cross in a more cephalic position than the fibers for the shoulder girdle segments. All of the fibers for the upper extremities make a higher decussation than those for the trunk musculature and the lower extremities. Significance of the Pyramidal De- cussation According to Cajal. The reason underlying the decussation of the pyramidal tract, as well as the de- cussation of other tracts in the nervous sj'stem, has been a perplexing problem. For what purpose or as the result of what causes the great fiber- crossings occur in the neuraxis is not clearly understood. Cajal, however, offers an explanation concerning decussation in general which seems as logical as itis ingenious. All decussation of tracts, according to Cajal's interpretation, depends upon the character of the vertebrate eye. The hemispherical, con- cave retinae with the biconvex lenses of the eyes make it essential that the optic fibers shall decussate in order that a proper mental perception of ex- ternal objects may be created. Cajal believes that the crossing of the optic fibers was, in all probability, inaugurated in the fish and cephalopoda. Primitively this decussation was complete and served as the organic means of determining a mental fusion of the separate visual images received by the two eyes. The corrected visual perception could not be created without the existence of a bilateral center in the brain, each half of which cooperated with the other. The optic decussation established the proper relations be- tween these bilateral visual centers and the two eyes. Furthermore, it exerted a decisive influence upon other pathways in the nervous system, consequent upon the reversal of the mental image in the brain. This reversal of the mental image necessitated a compensatory crossing of other tracts, especially in Fig. 232. — Diagram showing the distortion of tlie mental visual image of an object in lower vertebrates without an optic chiasm. (Cajal) L — Visual center. 270 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM the motor pathway. Such compensatoiy motor decussation in turn de- termined a crossing of the sensory tracts. In this manner the character of the verteljrate eye, which in the first instance enforced the complete cio.ssing of the optic fibers, ultimately determined all decussations within the central nervous system. Cajal's conception of the visual defects resulting from fail- ure of the optic fibei's to decussate is shown in Figure 232. The compensatory effects of a complete decussation in the optic nerves upon the motor and sen- ,sory pathways are shown in Figm'e 2.33. Rool Fibers of the Suboccipital Nerve. Upon either side of the interlacing bundles of the pyramidal decussation is the cephalic continuation of the ventro-paramedian sulcus. Still more lateral is the ventro-lateral sulcus, from which some fibers of the first cervical nerve (suboccipital nerve) occasionallj' make their emergence. These ventral root fibers of the first cervical nerve are often wanting at this level. The infrapj'ramidal portion on the ventral surface of the medulla is thus bounded upon the two sides by the right and left ventro-lateral sulci. The Pijramids. Passing upward along the ventral surface of the medulla into its pyramidal portion, the ventro- median fissure again reasserts itself in prominence and increased depth. The Fir> T^r,n + ;ir. cuL-iic it and sensory roots. A/— Crossed motor tract. tlOU « It U t nc DUU.lO-pOntlle SUlCllS. At O — Crossed optic nerves. R — Motor roots of tiie ii-,' l . i j i . ]' ^ ^,,„„ spinal cor.i. .S-Central tern,ination of crossed thlS IcVcl, the VCnt rO-mcdum fisSUrC """''"^ *^"^'' forms a deep incisure between two pronounced elevations which flank it. These elevations are the pyramids. They consist of two heavy strands of fibers, pyramidal in shape, with their bases resting upon the Ijulbo-pontile sulcus and their apices directed toward the most cephalic fibers of the pj'ramidal decussation. These two massive bundles, one on either side of the ventro-median fissure, represent an im- portant link in the pathway between the cerebral motor cortex and the spinal cord. They serve to conduct volitional impulses from the brain to the body musculature. The pyramids are relatively recent accessions and reach their greatest development in the higher mammals. They are especially promi- nent in man and the anthropoid apes, and may be regarded as indices to the degree of volitional control which has been acquired over the movements THE MEDULLA OBLONGATA 271 of the body. Their gradual attenuation in volume toward the caudal ex- tremity of the medulla is explained by the decussation of the crossed pyramidal fibers which move out of the ventral white column to take up their typical position in the lateral white colunm. This position they occupy throughout the entire length of the spinal cord. The ventro-median fissure, as it comes into relation with the bulbo-pontile sulcus, presents a deep pit partially hidden by the overhanging transverse fibers of the pons \'aroIii ; this is the foramen cecum posterius. Preolivarij Sulcus. Another feature of the ventral surface of the medulla is the confluence which takes place between the ventro-lateral and ventro-paramedian sulci at the junction of the upper and middle thirds of the medulla. At this level, the ventro-lateral sulcus sweeps for- ward to join the paramedian sulcus at the caudal extremity of the olivary eminence; thereafter the two sulci continue upward in a position lateral to the pyramids and ventral to the olivary eminence. In this relation the sulcus thus formed is known as the preolivary sulcus. It illustrates the disposition of the sulci in this region to be deflected ventrally as they ascend. In exceptional instances, the ventro-lateral sulcus gives rise to a few root fibers of the first cervical or sub- occipital nerve. The sulcus must be regarded as the prolongation of the groove which marks the point of emergence of the ventral root fibers in the spinal cord. It is a landmark indicating the line of the ventral motor cell colunm. Transition fron the Spinal Cord to THE Medulla as Seen upon the Lateral Surface. There is no distinct boundary hne to distinguish the lateral surface of the medulla from the lateral surface of the spinal cord. The cephalic extremity of this surface is marked by the bulbo-pontile sulcus and the acoustic division of the 8th nerve. The ventral boundarj^ of the lateral surface is the ventro-lateral sulcus, and its continuation the preolivarj' sulcus. The dorsal boundary of the lateral sur- face is the dorso-lateral sulcus. Postolivary Sulcus' In general appearance, the lower two-thirds of the lateral surface does not differ from the corresponding area of the spinal cord. The cephalic third, however, shows a marked increase in the ventro-dorsal diameter, together with the appearance of several conspicuous protuber- ances. The most dorsal portion of this surface shows a slight indenture which brings the surface into close relation with the floor of the fourth ven- tricle. In actual relation with this indenture is the lateral recess of the ven- tricle. One sulcus of considerable morphological importance traverses Fig. 34. — Diagram of the chiasm of the optic tracts and the central visual pro- jection in man. (Cajal.) c — Crossed fasciculus of the optic nerve, d — Direct fasciculus of the optic nerve, g — External geniculate body. Rv — Projection of the mental image in the visual cortex of the brain. 272 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM the lateral surface. Beginning at the caudal extremity of the medulla, the sulcus intermedins ascends vertically to the junction of the upper and middle thirds. Here, following the general disposition already observed in the ven- tro-lateral sulcus, this groove swings forward to take a position immediately orona Radiata Hr'ari of Caudate Nucleus Internal Capsule Optic Chiasm Oculomotor Ner\-e Optic Tract T^i^eminal Nerve; Portio Minor Triueminal Nerve; Portio r. ^^ Major ' IS- Abducens Ncrv-e Facial Nerve Acoustic and Vestibvilar Nerves Eminentia CMivans HypO!i;lussaI Ner\ e Vagus and Cllossopharyngeus NerM 3 Sjjlnal Accessory N 1 r\ e Eminentia Lati nlia Lateral Geniculate Body Mesial Geniculate Bady Inferior CoUiculus I^Ii Jdle Cerebellar Peduncle Tuborrulum Acousticum Enunentia Restiformis Eminentia Acoustica C UIK U3 Eminentia Trigemini Dor'*o lateral Sulcus Sulcus Interraediua Fio. 235. — Lateral view of the neuraxis with the internal capsule exposed. dorsal to the olivary eminence, where it is known as the postolivary sulcus. The importance of this sulcus is due to the fact that it marks the point of emergence of the spinal accessory or 11th cranial nerve. This is a motor nerve, although its fillers select a line of emergence different from that of the ventral root fibers. Consideraljle significance attaches to this fact. It seems to indicate an essential difference in the type of nerves which emerge from THE MEDULLA OBLONGATA 273 these two sulci. Nerve fibers maldng their exit from the brain-stem at the ventro-lateral sulcus supply somatic muscles. Nerve fibers escaping from the sulcus intermedius innervate muscles which have Ijeen derived in part from the gill arches. These muscles are the cephahc portions of the sterno-cleido- mastoid and the trapezius. Because tliey are skeletal in character but de- rived from branchiomeres, they are known as brandtio-motor nmsdes. The nerve supplying them is a branchio-motor nerve. This innervation establishes a fundamental difference between the muscles suppHed by fibers leaving the brain-stem through the vcntro-latcral sulcus and those leaving the brain- stem through the sulcus intermedius. The continuation of the sulcus intermedius to the position in which it forms the postolivary sulcus marks the points of emergence of two cranial nerves, the vagus nerve and the glossopharyngeus nerve. By far the larger portion of the postolivary sulcus is occupied by the emergence of the vagus nerve. The locus of emergence of these nerves indicates that their motor fibers belong to the branchial system and supply muscles derived from the branchiomeres. The postolivarj' sulcus also marks the site of entrance of a large group of afferent splanchnic fibers belonging to the vagus and glosso- pharj'ngeus nerves. In addition to the splanchnic sensory fibers which enter the brain-stem at the postolivarj^ sulcus, there are also others belonging to a group of special splanchnic afferents. These fibers arise in the taste-buds of the mouth and make their waj' into the central nervous system through the glossopharyngeus and facial nerves. "t 'entral Shift of the Dorsal Root Entrant Zone. The entrance of the splanch- nic sensory fibers into the neuraxis by means of a sulcus so far forward affords a notable feature of this level of the l)r;i.in-stem. There has been a slight tendency, however, for the entrant zone receiving the sensory root fibers of the upper cervical ganglia to move gradually awaj^ from its usual position in the dorso-lateral sulcus and occupy a more lateral area. This tendency has been carried to an extreme degree with the entrance of the dorsal root fibers of the vagus, glosso-pharyngeus and facial nerves. It has its explanation in the fact that the dorsal white cohunn in the medulla beings to assume a character different from that found in the spinal cord. New masses of gray matter crowd into this column which make necessary the ventral shift of the dorsal root entrant zone. Eminences on the Lateral Surface. In the caudal portion of the lateral surface, two eminences may be distinguished. The more ventral of these prominences is the eminentia lateralis. The direct cerebellar tract in this region is collected into a more compact Ijundle and produces a shght elevation upon the surface. This eminence is hmited ventrally by the ventro-lateral sulcus and dorsally by the sulcus intermedius. The second prominence is the eminentia trigemini, also known as the tuberculum trigemini. This eminence makes its appearance in response to the rapidly increasing amount of sul)- stantia gelatinosa in the dorsal gray column, augmented by the large col- lection of fibers forming the descending root of the fifth nerve. In the cephahc portion of the lateral surface, three distinct eminences make their appearance. 18 274 FORM AND FUNCTIONS OF THF CENTRAL NERVOUS SYSTEM 1. A largo prutuln'raiicc! dofiiKMl by the prcolivary and postolivary sulci and dorsal to the pyramids, the emincidia olivaris. This eminence is the surface expression of a. large coUocfion of specialized gray matter situated in the medulla olilongata, the inferior olive. 2. Immediately dorsal to the postolivary sulcus, is a well-defined swell- ing, the eminentia acoustica which extends from the bulbo-pontile sulcus for some distance caudally on the lateral surface. 3. The eiiiinentin redijonnis is llie most dorsal of the three eminences. It is due to the progressive dorsal migration of the dorsal spino-cerebellar tract and the augmentation of this bundle by fibers from the inferior olives. The combination of these two groups of ascending filx'i's, one from the dorsal spino-cerebellar tract, the other from the inferior olives, constitutes the inferior cerebellar pedunelc, which is also known as the resiiform body. Transition fhom the Spinal Coed to the IMluulla .vs Seen upon THE Dorsal Surface. In the description of the dorsal surface of the me- dulla, a ventricular and an infraventricular portion may be distinguished. In man, thi' ventricular portion occuiiics less than half the dorsal sur- face. In many of the l(n\ci \-ertel nates, it occupies the entire dorsal surface. It is appareiil frdiu I his fact that some of the importance attached to the formation of the \-entricl(t has diinimshed in the higlier verteljrates. The reduction in th(.' aiiK.iuiit of central gray matter may account for the relative decreas<' in tfie size of the fourth ventricle. The infraventricular jiortion of tlie dorsal surface of the medulla has no distinct lioundar>- line to sepaiate it from the spinal cord. Its cephalic bouudar)' is nuiTked \ix I lie a.pjieai'aiict' of t tie: fourth ventricle. The entire surface presents a gradual iiK'rease in its transverse diameter as it ascends. Upon reaching the junction (if its u]5per aiul njitklle tliirtls, it Ijegins rapidly to increase until its iliainetei' is double that of the spinal coril. S\dc> of the l)(irslongata, it is clear that certain structures make their appea,rance which are not seen in the spinal cord. The functional significance of these structtu'es is important in the interpretation of the internal organization of the medulla oblongata. On the ventral surface, the most conspicuous structures are the pyram- idal ih'cir.isation and the pi/ra)/iiih. The pyramids indicate an accession on the part of the brain-stem of a relativelj' recent pathwaj' which connects the firaiii with the spinal cord and affords a means of communicating voh- tiorial control 1o the muscles of the bod>'. The decussation of the pyramids is indicatiA'e of Ihe jia.rliid or curnpli-le crossing of the pyramidal tract which determines the contrahileral roiurol of one hemisphere of the brain over the muscles of the body. The sigmticance of this crossing as interpreted liy Cajal has already' liecm given. On the lateral surface the riinnciitia laU'raUs indicates the increasing prominence of the dorsal spmo-cereliellar tract as it ascends on its way toward the formation of tlie inferior cerebellar peduncle. The eminentia trigetaini indica,tes the position of the increasing mass of nerve-cells which receive sensory impulses fronr the face and head, the substantia gelatinosa. Included in this eminence is the descending spinal trigeminal tract which conveys sensory impulses from the Gasserian ganglion. The enniientla ulivans is tlie largest eminence of the lateral surface. THE MEDULLA OBLONGATA 277 It indicates the position of the inferior olive unci is important functionally because of its probable relation to the coordination of head and ej-e movements. The restiform body is a continuation of the lateral eminence with accre- tions of fibers received from the inferior olives, the combined collection forming the inferior cerebellar peduncle. This is the main patliway from the muscles to the cerebellum, and constitutes the afferent portion of the reflex arc which utilizes the cerebellum as its special center for synergic control of muscular activity. The eminentia acoustica is a prominent protuberance at the cephahc extremity of the lateral surface, and takes its significance from the fact that it marks the primary receiving center for nerve fibers coming in from the spiral ga^ujlion situated in the internal ear. This receiving center serves the purpose of conveying auditory impulses to the brain. On the dorsal surface the chief feature is the fourth ventricle, the signifi- cance of which in connection with the expansion of the central gray matter has already been discussed. The eminenUa clavw and eminentia cunei mark the cellular increase in the gray matter of the dorsal white columns, due to the appearance of relay nuclei which serve to convey sensory impulses from the legs, trunk, arms, neck and back of the head to the brain. These tracts act almost exclusively in the interest of discriminative sensiliility. Nerves Connected with the Medulla Oblongata. Six of the cranial nerves are connected with the medulla oblongata, namely, the hypoglossal or twelfth; the spinal accessory or eleventh; the vagus or tenth; glosso- pharj-ngeus or ninth; the auditory or eighth; and the facial or seventh. One of these, the hypoglossal nerve, belongs exclusively to the somatic motor system and supplies the muscles of the tongue with motor impulses. Three of these nerves belong to the mi.xed type and contain fibers of the splanchnic motor and splanchnic sensory components. These are the vagus, the glossopharyngeus and the facial nerves. The vagus nerve by its splanchnic motor component, innervates the pharynx, the larynx, the esophagus, the stomach, the small intestine, the heart, and the smooth musculature of the trachea and bronchial tree. By its splanchnic sensory component it innervates the pharynx, the larynx, the esophagus, trachea and lungs, the stomach and small intestine. It also supplies a small cutaneous branch to the auricle of the ear. This, prob- ably, is an aberrant fasciculus associated with the trigeminus nerve. The vagus also has a small component of the special splanchnic sensory element supplying the taste-buds in the pharynx. The glossopharyngeus nerve, by its splanchnic motor component, supplies the muscles of the pharynx and some of the palatal muscles; by its splanchnic sensory component it innervates the pharynx and part of the soft palate. The posterior third of the tongue is innervated by the special splanchnic sensory portion of the glossopharyngeus nerve. The facial nerve, by its splanchnic motor component, innervates all the muscles of facial expression, while by its splanchnic sensory component. 278 FOKM AND FtTNCTIONS OF THE CENTRAL NERVOUS SYSTEM ■3Z t*-^ t. d 0/ h X -0 3 9 3 i^ K-o 3 C Z ? &=" b !;: c--' o 2; -|_ C' '~ o 9 < §"■-' THE MEDULLA OBLONGATA 279 through the chorda tympani, it serves as a special splanchnic sensory ele- ment for taste over the anterior two-thirds of the tongue. One of the cranial nerves connected with the medulla oblongata is ex- clusively concerned with highly specialized somatic sensory impulses. This is the auditory or eighth nerve which, by means of its vestibular and acoustic divisions, mediates the transmission of impulses necessary for equihbratory control, as well as those concerned in audition. 3d Vcntricl. Caudate Nucl Thalan Inferior Colliculus Superior Collieulus Pineal Body Pulvinar of Thalamus Mesial Geniculate Body Lateral Geniculate Body Nerve Xerve 7th Nerve Sth Nerve Cerebral Peduncle Trigonum Lemnibci Superior Cerebellar Peduncle Cut Edge of Cerebellar Peduncle 12th Nerve Occipital Bone Atlas Vertebral Artei-y 0th Nerve 10th Nerve 1 Uh Nerve Tentorium Cerebelli Ventricle Funiculus CuneatUB Gracilis Spinal Cord 2d Cervical Nerve Fig. 238. — View from dorsal aspect of upper part of spinal cord, medulla oblongata, pons, fourth ventricle, midbrain and thalamus, dissected in silit. (J. Symington.) The spinal accessory nerve is characterized by the fact that it emerges from the l^rain-stem in the sulcus intermedius and supplies muscles which in part are derived from the branchial arches. It constitutes the branchio- motor supply of the trapezius and sterno-cleido-mastoid muscles. The hypoglossus nerve emerges from the proolivary sulcus and is re- presentative of the somatic motor cell column, supplying muscles derived from myotomes. The motor portions of the facial, vagus and glossopharyngeus nerves 280 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM emerge from the postolivary sulcus and are representative of the lateral motor cell column, supplying muscles derived from branchiomeres. The emergence of the accessory portion of the spinal accessory nerve from the sulcus intermedius may be regarded as significant of the transition in type from somatic to branchial musculature in passing from the trunk to the head. This transition might be expected in the formation of such muscles as the trapezius and sterno-cleido-mastoid, which are in part branchiomeric and in part myotomic. The Dorsal Root Ganglia of the Cranial Nerves Connected with the Medulla Oblongata. Two of the cranial nerves connected with the medulla have no dorsal root ganglia, i.e., the spinal accessorj' and the hypoglossal nerves. Embryologicallj', the h3-pogIossal nerve in the earh' stages of develop- ment has a portion of the neural crest in connection with it which, in rare instances, persists as a variant. When present, this is known as Froriejj's ganglion. The spinal accessory nerve in man likewise has no dorsal root ganglion, although in its early development it is in close relation with an extensive portion of the neural crest from which the root ganglia take origin. The vagus nerve has a small dorsal root ganglion situated in the jugular foramen, known as the ganglion jugulare. This ganglion develops from the neural crest. In addition to this ganglionic structure, the vagus has a trunk ganglion, the ganglion nodosum. This is much larger, and is situated in the neck dorsal to the internal carotid artery and ventral to the superior cervical ganglion of the sympathetic. It differs from the root ganglion of the vagus in the fact that it arises from a placode of the ectoderm in connection with the fourth branchial pouch. The glossopharyngcus nerve, like the vagus, has two ganglia. The dorsal root ganglion, the ganglion superius, is situated at the upper orifice of the jugular foramen; the trunk ganglion, called the ganglion petrosum, is situated in a small depression at the lower orifice of the jugular foramen. The ganglion superius is also known as the ganglion of Ehrenritter (1790), and the ganglion petrosum, liearing the name of its discoverer, is called the gaiigluin vf Andcrscli (1791). The tnmk ganglion develops from a placode in connection with the thiril Iiranchial pouch, while the root ganglion takes origin from tlie neural crest. The auditory nerv<> has a dorsal root ganglion connected with each of its two divisions. The ganghon in relation with the cochlear division is the ganglion .spirale or ganglion of Corti. It is situated in the base of the lamina spiralis. The ganglion in relation with the vestibular division is the ganglion of Scarpa, which is situated at the external extremity of the internal auditory canal. The facial nerve has a small dorsal root ganghon, the ganglion genicula- lum, situated at the beginning of the facial canal in the petrosal portion of the temporal bone and immediately dorsal to the hiatus Fallopii. It serves as the root ganglion for the chorda tympani, and its dorsal root fibers con- stitute the pars inlermedia of Wrisberg. ^ CHAPTER XM THE MEDULLA OBLONCJATA INTERNAL STRUCTURE AND HISTOLOGY OF THE MEDULLA Rearrangements of the Gray and White Matter in the Medulla. Al- though the medulla oblongata consists of the same elements as the spinal cord, there is much rearrangement in its graj' and white matter. These changes seem to serve several purposes. In the first place several, ascending and descending tracts take up new positions by crossing from one side to the other. Such crossings, if Cajal's explanation of decussation in the nervous system be accepted, are in the interest of adapting the neural mechanism to the optical requirements imposed by the vertebrate eye. The second purpose of the rearrangement in the medulla affects the gray matter. Its object is to maintain an adequate control in the autonomy of its splanchnic and other special functions while adapting itself to the alterations resulting from decussations in the white matter. These changes occur gradually and in regular order. The difference in appearance between the cross section of the upper cervical segments and the cross section of the caudal portion of the medulla is slight. The differ- ence between the cross section of the spinal cord and that of the cephalic extremity of the medulla is so pronounced that it may be appreciated only by following the changes in serial order. Seven critical levels of the medulla have been selected to illustrate the alterations in the relations of the gray and white matter. Before con- sidering these changes, it is necessary to review the standard arrangement of the two chief constituents of the neuraxis as seen in the upper cervical segments of the spinal cord. A cross section of such a spinal segment reveals the bilateral symmetry in the two halves of the cord with a dividing line between them indicated by the dorso-median septum and the ventro-median fissure. Each half of the section comprises in its white substance a dorsal white column, a lateral white column and a ventral white column. The gray matter is made up of a ventral, a lateral and a dorsal gray column, while the two halves of the sec- tion are connected across the midline by a gray commissure, or central gray 7natter, and a white commissure. All the changes in the medulla either depend upon alterations in the relations of these constituents or are due to the introduction of new elements. The seven critical levels selected in the medulla are: 1. The caudal hmit of the pyramidal decussation. 2. The middle of the pyramidal decussation. 281 2S2 FOKM AND Ft'XCTIOXS OF THE CENTRAL NERVOUS SYSTEM THE MEDULLA OBLONGATA 283 3. The cephalic limit of the pyramidal decussation. 4. The caudal Hmit of the fillet decussation. 5. The caudal limit of the inferior ohve. 6. The middle of the inferior olive. 7. The summit of the inferior olive. Changes in the Gray and White Matter at the Level of the Lower Limit of the Pyramidal Decussation. Changes in the Gray Matter. "Upon comparing a section of the medulla oblongata at the level of the lower limit of the pyramidal decussation with the section of the upper cervical segment, certain slight changes in the gray matter are to be observed. 1. The ventral gray column is much smaller. It is partially cut off from the central gray suljstance by pyramidal fibers. These fibers are pursuing an obhquely horizontal coui'se and making their way from the ventral white column, backward and outward, across the midline toward the contralateral white column. The ventral gray column has the appearance of an isolated collection of nerve cells. This isolation of the ventral gray cokimn is usually more marked on one side than on the other, for the reason that nearly all of the p3'ramidal fibers have previously made their decussation. Those fibers which are still crossing represent the few fascicuh which have yet to enter the pyramidal decussation. There are two distinct clusters of motor cells in the ventral gray column; one situated ventro-niesially and the other ven- tro-lateralty. Both clusters give rise to emergent nerve root fibers which go to make up the motor portion of the first cervical (suboccipital) nerve. 2. The lateral gray column has increased in size, especially near its base. It does not present so pronounced an apex as is the case in the cervical region. At its base is a crowded cluster of large motor cells constituting the liucleus ventralis accessorius, which gives rise to some of the accessory fibers of the eleventh cranial nerve. 3. The reticular formation has increased not only in size, but also in the richness of the distribution of the gray matter in it. It occupies a position bounded bj^ the caput, body and neck of the dorsal gray column, dorsally; by the central gray matter, mesially; by the ventral gray column, ventrally; and by the lateral white column, laterally. Some of the fibers of the crossed pyramidal tract, at this level, lie in close relation to the outer margin of the reticular formation, while some of the horizontal fibers in the pyramidal decussation traverse the reticular formation on their wa}' toward the crossed pyramidal tract. 4. The dorsal gray column is much increased in size and has moved later- ally away from the dorso-median septum. Its caput is especially enlarged, due to the increase in the amount of substantia gelatinosa, whose volume at this level has become sufficient to produce a slight protuberance upon the lateral aspect of the medulla, the emincntia trigemini. The neck and body of the dorsal gray column are both shorter and thicker. Certain large nerve- cells are situated in the position of the mesial basal group, occupying an area similar to that of the posterior vesicular column of Clarke. These cells are 284 FORM AND FXTNCTIONS OF THE CENTRAL NERVOriS SYSTEM Fig. 240. — Serial sections of Iirain-stem Nos. 20 ami ol sliowiii^ tlie pyramidal decussa- tion, the detachment of the ventral gray columns from the central gray substance, the general enlargement of the latter, the increased size of the dorsal gray column, and the efl'ect of dec\issatioii upon the ventro-niedinn fissure of the medulla oblongata. THE MEDULLA OBLONGATA 285 Fic. 241. — Serial sections of brain-stem Nos. 4S and 62, showing the marked effects of the pj'raniidal decussation upon the internal configuration of the medulla oblongata. Sections Nos. 20, 34, 48 and 62 intervene lietween the caudal level of the p}'ramidal decussation and the next more cephalic le^'el \yhich is laljelled in detail. These intervening sections illustrate the gradual process of rearrangement in the gra}- and •white matter. 2S6 FORM AND Fl'NCTIOXS OF THE CENTRAL NER^'OUS SYSTEM no doul;>t closely related in function to those of Clarke's column. Numerous reflex collaterals from the entrance zone of the upper cervical nerve make their way across the neck and body of the dorsal gray column in the direction of the ventral si'ay column. .). The central grmj iiudter has also increased in size; it has the appearance of a cjuadrilateral structure cjuite dissimilar to the narrow commissural band which stretches from side to side in the cervical region. This change in the central gray matter is one of the most striking alterations observed in the gray matter at this level of the medulla oblongata. There is also a slight tendency for the central gray matter to move further dorsally, as if in process of extending toward the dorsal surface of the medulla. This dorsal migration of the central gray matter is a movement of much importance in the subsecjucnt changes in the meduha oblongata. The central canal is cen- trallj' placed. In many instances this is a distinguishing feature of the medulla since, as a rule in adult life, the central canal in the spinal cord becomes obliterated or replaced b_y a cluster of ependymal cells. Ventro- lateral to the central canal is a group of medium sized motor cells constitut- ing the nucleus dorsalis accessorii which gives rise to emergent root fibers of the spinal accessoi'y nei'vc. Along the dorsal border of the central gray matter, mesial to the collection of cells forming the mesial basal group, is a fairly large sized collection of finely mcdullated nerve fibers constituting the fasciculus lomjitudutaUs dorsalis of Schtitz. This fasciculus probably rei>resents an ancient motor pathwaj^ in the central nervous sj'stem. 6. No new elements in the gray matter have made their appearance at this level. Changes hi the White Matter. 1. The dorsal white columns are both much more extensive in their transverse diameters. They are divided into two fasciculi, the fasciculus gracilis, situated mesial to the dorso-paramedian sulcus, and the fasciculus cuneatus, occupying a position lateral to this sulcus. The enlargement of the column is due to the addition of many ascending fibers to the tracts of GoU and Burdach. Some axones situated at the junction of the dorsal white column with the dorsal gray column indicate the entrance of dorsal root fif)crs of the first cervical nerve. These fibers make up a relatively small root entrance zone. 2. The lateral white column presents the circumferential, intermediate and juxtagriseal zones. In the circumferential zone, tlie tract of Lissaucr is much reduced in size and occupies the most dorsal position. Immediately ventral to it is a rela- tively large fasciculus of descending fibers which constitutes the descending or spinal root of tlie trigeminal nerve. Numerous collaterals from this tract end in the substantia gelatinosa. Ventral to the descending root of the fifth nerve is a large t>undle of fibers, the dorsal spino-cerchellar tract (tract of Flechsigj. The ventral spino-cerebellar tract (tract of GowerJ occupies a position ventral to the tract of Flechsig, and a small triangular bundle, the olivospinal tract (tract of Helweg) completes the lateral circumference. The intermediate zone contains in its most dorsal position the crossed pyramidal tract, ventral to which are the rubrospinal, the lateral Dcitero- spinal and the spino-thalamic tracts. THE MEDULLA OBLONGATA 287 The jiixtagriseal zone contains some of the crossed pyramidal fibers turning from thoir horizontal into their vertical course. It is made up in the main by the fibers entering the reticular formation. 2. The lateral gray column is somewhat increased in size. It contains an extension of the nucleus ventralis accessorius and, together with the ventral gray colunm, is separated from the remaining gray matter of the medulla. 2SS FORM AND Fl'XCTIOXS OF THE CENTRAL NERVOUS SYSTEM 3. Tho reticular formation is reduced in size and niucli obscured by the decussating pja-amidal fillers. 3. The ventral white column is distinguished at this level by the pyramidal • '- *«f. Fic;. 243. — Seriul sections of brain-stem Xos. 109 and 135, shownig the rearrangements in the si'^-Y s-nd white matter incident to the pyramidal decussation. These sections represent interveninn; levels between the middle of the pyramidal crossing and the cephalic extremity' of this decussation. fibers which make their way dorso-laterally to a position in the crossed ]3yiaTiiidal tract. Tliese fibers represent the caudalmost elements in the THE MEDULLA OBLONGATA 289 pyramidal decussation. There are also other pyramidal fibers which do not decussate at this level but remain uncrossed until they reach the spinal cord. These fibers constitute the direct pyramidal trad (fasciculus of Ttirck). The ventral white column contains the ventral Deitero-spinal and the tecto- spinal tracts. 4. The netv elements in the white matter at this level are the pyramidal decussation and the fasciculus longitudinalis dorsalis of Schiltz, an ancient motor pathway in the neuraxis. This fasciculus is incorporated in the dorsal portion of the central gray matter. Emergent and Entrant Root Filjers at this Level. Two groups of emergent root fibers appear at this level of the medulla oblongata. First, motor fibers arising from groups of motor cells in the ventral gray column and constituting the ventral root of the fir.st cervical nerve. The second group of emergent root fibers arise from the two nuclei of the spinal accessory nerve. The course of these emergent fibers is of moment and should be described in detail. The ventral root fibers of the first cervical nerve make their way forward and outward to the ventro-median sulcus, where thej' emerge in line with the other motor root fibers of the cervical, the thoracic and the spinal nerves. The emergent fibers from the two nuclei of the spinal accessor}' nerve sweep backward, inward and then out- ward until they reach a point of emergence immediately in front of the anterior margin of the dorsal gray column. Here thej' make their escape from the medulla in the sulcus intermedius. This circuitous course in emerging from its origin is a characteristic, not only of the spinal accessory nerve, but also of the cranial nerves which belong to the same system as the eleventh nerve. A few. dorsal root entrance fibers occupy the usual zone and represent the sensory elements in the suboccipital nerve. In many instances these sensory elements are entirely wanting. Fissures and Septa. Several clianges occur in the fissures and septa. Among these is the decrease in depth of the ventro-median fissure caused by the crossing pyramidal fibers. The dorso-median septum has lost the appearance of an actual septum and has become a deep fissure extending from the dorsal surface of the medulla to the dorsal surface of the gray matter. The other sulci, marking the point of entrance and emergence of the nerve roots as well as the position of the paramedian septa, correspond in all details to those in the spinal cord. Changes in the Gray and White Matter through the Middle OF the Pyramidal Decussation. Changes in the Gray Matter. 1. The ventral gray column has become still further reduced in size as compared with the level just described. It is now isolated from the rest of the gray matter of the medulla and surrounded by white substance. This isolation, giving the ventral gray column the appearance of an island, is brought about by the pyramidal fibers which are decussating at this level. In the ventral portion of this collection of gray matter are a few scattered cells repre- senting motor elements of the first cervical nerve, while the major portion of the gray matter is occupied by a large group of motor cells constitutmg the ventral accessory nucleus. 1(1 290 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM 4. The dorsal gray column is enlarged, due to the increase in the sub- stantia gelatinosa. It has moved further away from the dorso-median fissure by reason of the increase in size of the dorsal white column. The neck and body of the dorsal gray cohnnn are shorter and thicker than in the lower level, and there is no evidence of the mesial basal group of cells representa- tive of Clarke's column. 5. The Central Gray Mailer. This portion of the gray substance shows a still further enlargement and a mai-ked tendency toward dorsal migration. It lies about midway between the ventral and dorsal surfaces. The central canal has increased in size, and the nucleus dorsaUs accessorius is presented as a collection of cells situated at its ventro-lateral margin. On the dorsal margin of the central gray matter are the filiei's which constitute the dorsal longitudinal fasciculus of Schiiiz. 5. No new elements of gray matter liave made their appearance at this level of the medulla oblongata. Changes in the White Matter. 1. Tlie dorsal white columns are liroad and their separation into the fasciculus gracilis and fasciculus cuneatus is more pronounced because of the increasetl prominence of the dorso-paramedian sulcus and septum. There is no root entrant zone and in certain respects the white matter resembles the reticular formation; tliis appearance is caused \>y the richness of the septal processes in the dorsal white column. 2. The Lateral White Column. This column has become narrower, while the reticular forniatinn is reduced in size and obscured by the massive cross- ing of the pyramidal fibers. The three zones are still discernible The circumferential zone is made up of its characteristic tracts, the des- cending or spinal root ' musculatui'e is accomplished. Emergent Root Fibers. The only emergent root fibers at this level are those arising in the ventral and dorsal nuclei of the spinal accessory nerve. THE MEDULLA OBLONGATA 291 Those ventral root fibers taking origin in the ventral gray eolunm and des- tined to enter the suboccipital nerve, descend for a considerable distance in the reticular formation before they make their emergence from the neuraxis. There are no sensory root fibers entering the medulla at this level. Fissures and Septa. The ventro-median fissure is almost obliterated because of the interlacing of the fibers in the pyramidal decussation. This fissure appears as a shallow cleft extending inward for a short distance and then forking, so that one branch turns to the left and the other to the right. Both of these divergent limbs of the ventro-median fissure result from the crossing fibers of the pyramidal decussation. This forked appearance of the ventro-median sulcus is seen nowhere else in the neuraxis. The dor so-median sulcus has l)ecome a pronounced fissure extending from the dorsal surface of the medulla to the dorsal aspect of the central gray matter. In its more dorsal portion, there is some tendency for this fissure to show a still greater divergence of the white columns which bound it. This divergence eventually results in the appearance of the floor of the fourth ventricle. Changes in the Gray and White Mattek at the Level of the Ceph- alic Limit of the Pyramidal Decussation. Chatiges in the Q ray Matter. 1. The ventral gray column, almost completely isolated by the decussat- ing fibers of the pyramidal tract, is much reduced in size. It still contains some nerve cells which give rise to fillers of the spinal accessory nerve. 2. The lateral gray column is shghtlj^ larger than in the lower section. It also contains a portion of the nucleus ventralis accessorii. 3. The reticular formation has been invaded by the crossing fibers of the pyramidal tract. It is in this manner obscured and somewhat reduced in size. 4. The dorsal gray columns have migrated laterally until they lie shghtly dorsal to the transverse diameter of the section. The gray matter is increased in size by still further additions to the sub- stantia gelatinosa. The neck and body of the dorsal gray column have lost definite outhne due to the appearance of other masses of gray matter. 5. The central gray matter shows a still further tendency toward dorsal migration, and the central canal is somewhat larger than in the lower sec- tions. In its ventro-lateral margin, it contains the nucleus dorsahs acces- sorii. In its dorsal margin is the fasciculus longitudinalis dorsahs of Schiitz. 6. New Elements in the Gray Matter. Several new masses of gray matter have made their appearance at this level and represent elements of major importance. The first of these is the nuclcns gracilis, a collection of gray matter situated immediately adjacent to the dorso-median fissure and projecting into the column of Goll. This nucleus serves as a relay station for the fibers ascending in the fasciculus gracilis, which, by means of synapses, form a part of the pathway for discriminative sensibility. The nucleus extends from the dorsal aspect of the central gray matter to the dorsal periphery of the medulla. Immediately lateival to it is another new mass 292 FORM AND FUNCTIONS OF THE CENTRA!. NERVOUS SYSTEM of gray iiiatter, the nucleus cuneatus. This nucleus extends from the dorsal margin of the central gray toward the periphery of the column of Burdach. The the surf rise to tl appearance of these new masses of gray matter causes changes upon ace which li;iv(> already l)een mentioned, the nucleus gracilis giving he eir]inenlia clavie.the nucleus cuneatus giving rise 1o the eminentia THE MEDULLA OBLONGATA 293 euneL This level of the medulla oblongata contains in its more dorsal aspect RTOups of cells which serve to relaj- sensory impulses from all parts of the Serial Section No. 213 Serial Section No. 2.31 Fic. 24.5. — Four intervening sections between the cephalic level of the pyramidal clccn.ssa- tion and the caudal level of the fillet decussation. body to their final sensory areas in the hi'ain. These groups of cells are collected in three nuclei, the nucleus gracilis, which relays impulses receivetl from the legs and lower trunk; the jvicleus cnucatus, which relays impulses received from the arms, upper trunk and neck; and the nucleus contained in the substcmtia gelatinosa, which relays nnpulses received from the head, face and cavities of the head. A line drawn transverseh* through the central canal at this level would bound a region upon the dorsal aspect of the neuraxis devoted to the relay of sensory impressions coming from the entire body. For the most part, these impressions are concerned in discriminative sensibility. In the case of the head and face, however, it is probable tliat all types of sensibility, including pain and temperature, rccei\-e their relay in the nucleus represented by the substantia gelatinosa.. In tliis respect, the medulla oljlongata does not differ fi'om the spinal cord, the dorsal region of which is largeh' concerned with the transmission of discriminative impulses. 294 J'ORM AND FlTNt'TK.tNS (IF THE CENTRAL XEKVOUS SYSTEM Another new element ;ii)i)e;u'ing at this \evo\ is a .small mass (jf graj' matter situated dorsal to the substantia gelatinosa ami surrounded by fibers of the fascieulus runealus. This is an acccssurii partioit of the sub- stantia gelatino.sa. Chaiigcs in the White Matter. 1. The dorsal white column is much smaller, as it now contains the nucleus ('uneatus and nucleus gracilis which occupy some of tlie space formerly taken up by ascending fibers of the two dorsal tracts. 2. The Lateral ]\'hite Coluirm. An important change is determined by the small number of jiyramidal fibers in the intermediate zone. The circumferential zone contains its usual elements, i.e., the dcscendiJig spinal tract of the trujeniinal nerve, the dorsal .•- matt(M- .-md Ihe appearance of the nu- cleus gracilis. The other sulci are similar in all respects to tliose jireviously described in connection with the lower levels of the medulla oblongata. CHANGE.S IN THE GrAY AND WlIITE MaTTER AT THE LeVEL OF THE Caudal Limit of the Fillet Decuss.vtion. Cluinges in the Gray Matter. 1. The ventral gray column at this level has disappeared, or at most con- sists of a few scattered groups of nerve-cells constituting the cephalic ex- tremity of the ventral accessoiy nucleus of the eleventh cranial nerve. 2. The lateral gray column has also disappeared, with the possible excep- tion of some scattered motor cells representing el(>ments in the ventral accessorv luieleus. THE MEDULLA OBLONGATA 295 3. The reticular formation has again resumed its former proportions and IS now divisible into a mesial gray portion, tin- formatio reticularis gnsea, and a lateral portion, the formatio reticularis alba. In this region the reticular formation takes on a special significance, as it is probable that the gray portion of it constitutes one of the chief elements in the control of respira- tion and represents in part, at least, an extensive nucleus reaching from this 296 FORM AND FUNCTIONS FO THE CENTRAL NERVOUS SYSTEM point to the lower triangle of the floor of the fourth ventricle, which con- stitutes the chief regulating respirator^' nucleus. 4. The dorsal gray column has increased in size by additions to the substantia gelatinosa. It lies directly in the transverse axis of the section. It does not occupy a i>osilioM (juite so close to tlie peripherA^ l^ut has inter- posed between it and the margin of the medulla two groups of fibers, the external arcuate Jlbers and the descending root of the trigeminal nerve. The neck and bodv of th(_: dorsal gra,y column have disappeared and the gra}' sub- stance is now separated from the central gray matter by the appearance of an important group of crossing fibers which constitute the decussation of the inesial jdlct. 5. The central gray matter is oval in form and much larger in size. In its dorsal migration, it is entering upon its last stages. A small tongue-hke prolongation of the dorsal i:)orti(ni of the central gray matter iria,kes its way into the dorso-median septum, as if liy this wedge the dorsal columns are thialh' made 1o diverge, and tlie central graj' matter itself comes into the floor of the fourth ventricle. This tongue of graj" matter varies in size and conspicuity in diff(;rent spccinuars. The central canal has become en- larged and is jiresent as an elongated slit extending from the ventral portion lit the central gi-ay matter toward its dorsal aspect. Along the miQ-gin of tfie central gray matter are scattered groups of cells, the most ventral of which represents the caudal portion of the nucleus lii/jioglo.^si. This nucleus gives rise to the twelftfi cranial nerve. Dorsal and lateral to this group of cells is tlio c(jntinuation of the nucleus dorsaUs accrssorii, and between these two nuclei is the caudal extremity of the (/or.soi nucleus of the i'agu-\ (nucleus dorsalis vagi). Along the dorsal margin of the central graj' matter, situated upon either side of the tongue-like process wliich projects into the dorso-median septum, are the fibers constituting the fasciculus longitudi nuli.s dm'sidis o) Sclruf:. 6. A'Cin Elements of the (Jruij Matter. Several new elements in the gray matter have made their appearance. Among these are two specialized col- lections of nerve cells situated lateral to the collected bundles of the pj-raniids, the paroliva ventralis and dorsalis respectively. Another new portion of gray matter at this level is situated on the vent ro-lateral aspect of either pyra- mid. This is the nucleus arciformi.'i. Alention has previously been made of the appearance of the dorsal nucleus of the vagics nerre in the central gray matter. The nucleus gracilis has increased in size and fills tlie entire region of the fasciculus gracilis. The nucleus cuneatus has likewise increased in size and has connected with it many smaller, scattered masses of gray matter. Changes in the White Matter. 1. The dor.sal white column is smaller, because of the increase in the dimensions of the nucleus gracilis and nucleus cuneatus. 2. The lateral ivkite colmnn is also smaller in its dimensions, but its three general zones may be distinguished. The circumferential zone con- tains the descending root of the trigeminal ner\'i', now a massive liundle, THE MEDULLA OBLONCATA 29^ ventral to which hes the dorsal spino-cerebellar tract, at this level collected into a triangular fasciculus. Immediately ventral to the tract of Flechsi"- Serial Section Xo. 262 Serial Section No. 276 Fig. 247. — Two intervening sections between the caudal level of the fillet decussation and the caudal limit of the inferior olive showing paroliva and nucleus arciformis. is the ventral spino-cerebellar tract and the olivo-spinal tract of Helweg. The intermediate zone contains no pj'ramidal fibers; it is made up of the 298 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM rubro-spmal tract, the spino-thalaniic tract and the lateral Deitero-spinal tract. It also contains the forniatio reticularis allja. The juxtagriseal zone consists of the forniatio reticularis grisea, which is in contact medially with the crossing fibers of the fillet decussation. 3. The ventral white column is made up of the collected mass of pj'ramidal fibers constitutina, the pyreiinids, whose surface e.\prcs.sion is seen in the pyra- midal eminence. In addition to this large mass of fibers are the tecto-spinal and ventral Deitero-spinal tracts. Deeply situated between the ventral aspect of the central graj' and dorsal limit of the ventro-median sulcus, are the crossing fibers of the fillet decussation. Some of these fibers have alreadj^ undergone tlecussation and are taking up their position as elements in the median fillet or lemniscus. 4. N'eu' Elements in the ]\'hitc Matter. The new elements in the white matter are the fibei's which determine the Jillet decussation. These are known as the internal arcuate filers. They have their origin in the nucleus cuneatus and the nucleus gracilis, and as axones of cells in these nuclei sweep forward on a horizontal plane encircling the central gray matter. They reach the midline immediately ventral to the central gray matter. Here they cross from one side to the other, thus occasioning a complete decussation which is known as the decu!<.^atio lenini.'ici or decussation of the fillet. This decus- sation affords the means whcrebj' impulses arising in one half of the body cross to the opposite half of the brain-stem and eventually enter into the contralateral cerebral hemisphere. Thus the sensory elements of conduction keep pace with the motor ti'act. The main sensory decussation occurs in close proximity to the niajiir motor decussation. By means of this decussa- tion in the sensory ];)athway, it is evident tliat impulses arising in the left leg, left arm or left side of the trunk are eventuallv conducted to the right hemisphere of tlie brain, where they liecome active as elements in consciousness. Another set of fibers which sweep around the margin of the medulla arises in the nucleus cuneatus and nucleus gracilis. It then passes, in succes- sion, the descending root of the trigeminal nerve, the dorsal spino-cerebellar and ventral spino-cerebellar tracts, as well as the tract of Helweg; it finally reaches the ventral surface of the pyrandds. These are the fibra; arcuatce externa; ventrales, which, after passing the pyramids, dip into the ventro- median sulcus and then proceed, in part at least, to the restiform body of the opposite side. This constitutes a means of communication between the nucleus cuneatus and nucleus gracilis, and the cerebellum. It probably indicates a connection which serves the purpose of bringing to the cerebel- lum the afferent impulses from the muscles necessary to synergic control. The significance of these external arcuate fillers in their relation to the cere- bellum on the one hand, and to the muscles on the other, is, however, a matter of deliate at the present time. The emerrjent root fibers are those of the spinal accessory nerve which follow their characteristic course backward, outward and forward, to emerge from the sulcus intermedius. In consec|uence of the tendency THE MEDULLA OBLONGATA 299 of the substantia gelatinosato move further ventrally, the sulcus intermedius is also following the same course and is gradually assuming a more ventral position. Fissures. The ventro-median fissure has resumed its regularity and prominence. It is relatively deep and presents no forking in its dorsal extremity. Its depth is somewhat decreased by the crossing fibers of the fillet decussation, so that there is a considerable distance interposed between the dorsal extremity of the ventro-median fissure and the ventral aspect of the central gray matter. The dorso-median fissure has become wider and is especially prominent on the surface where it is flanked on either side by the clavse. The depth of the fissure is considerably less than in the lower sections. Changes in the Gray and White IMatter at the Caudal Limit OF THE Inferior Olive. Changes in the Gray Matter. 1. The ventral and lateral gray columns at this level have disappeared. 2. The reticular formation is much larger and divisible into a mesial por- tion, the formaiio reticularis grisea, and a lateral portion, the formatio reticularis alba. 3. The dorsal gray column has lost its definition. The enlarged caput of the column is present as a much increased substantia gelatinosa which lies mesial to the large bundle of the descending spinal root of the trigeminal nerve. The neck and body of the dorsal gray column have disappeared, and a complete separation of this portion of the gray substance of the central gray matter is determined by the arcuate fibers sweeping forward and then inward from the nuclei of the dorsal white column. 4. The central gray matter shows the consummation of its dorsal migra- tion, and the tongue-like process noted before now projects between the opposed edges of the dorsal columns. These columns are diverging to permit the gray matter to form the floor of the fourth ventricle. The thin process of gray matter projecting between the lips of the dorsal columns is the obex. The central gray matter on its lateral and ventral aspects is invested by the internal arcuate fibers. In its most ventral portion, it shows a cluster of large motor cells, the nucleus hypoglossi. Immediately dorso-lateral to this nucleus is the nucleus dorsalis vagi. Dorsal to this is the nucleus dorsalis accessorii and in a still more dorsal position is the nucleus radicis spinalis glossopharyngei. Interposed between the nucleus hypoglossi and ihenucleus dorsalis vagi are the fibers which make up the fasciculus longitudinahs dorsalis of Schiitz. The central canal is an elongated space tending to occupy a more dorsal position in the central gray matter. 5. New Elements in the Gray Matter. The most important addition to the medulla oblongata at this level is the inferior olive (?iuclcus olivaris inferior) which presents itself as a thin band of convoluted gray matter con- taining cells of various sizes, many of which are large stichochrome cells. This collection of gray matter is situated dorso-lateral to the pyramids and ventral to the substantia gelatinosa. In connection with it are the parohva 300 F()R?.r AND FTXCTIOXS OF THE f'EXTILAL NERVOUS SYSTEM dorsalis ;ui(l (he paruliva venl lalis. The acccssmy |)ortions of the inferior olive are actuall>' iiifcKral parts of the f>liA-f' «liich appeal' as dotafhed from 00 6 ^; d o i H a r o the general mass of gray matter. Dorsal to the olive and ventral to the substantia gelatinosa, in a position about halfway lietwcen the two forma- tiones reticularcs allice, there appears a nucleus containing large Tuotor cells. THE MEDULLA OBLONGATA 301 From this nucleus fibers make their way dorso-mesiallj' where they come into relation with the dorsal nucleus of the vagus. They then turn forward Fig. 249. — Cross section through the medulla ul)longata, showing the approach of the central gray substance to the dorsal aspect of the stern as the fourth ventricle is about to appear. (Serial section No. 346.) and outward to reach the postolivary sulcus. This is the nucleus amhiguus, which gives rise to important fibers of tlie vagus nerve. In the intermediate zone of the lateral white column, immediately mesial to the ventral spino-cerebellar tract, appears the nucleus reticularis lateralis, while dorso-lateral to the substantia gelatinosa is a collection of small-sized cells forming the nucleus marginalis dorsalis of Ziehen. The nucleus gracilis and nucleus cuneatus occupy the entire dorsal column. The dorsal nucleus of the vagus has increased in size. It contains large cells of the motor type and many smaller cells which serve in a capacity of sensory relays. The nucleus arcijormis has enlarged and become more mesial in its position. Changes in the White Matter. 1 . The dorsal white column has disappeared, with the exception of a few ascending strands of the column of Burdach, in relation with the nucleus cuneatus and the nucleus cuneatus externus. 2. The lateral white column is reduced m size, due not only to the removal of the pyramidal tract, but because of the appearance of the inferior ohve. 302 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM In the circumferential zone, the most dorsal element is the descending spinal tract of the trigeminal nerve. Its external surface is crossed by a few of the external arcuate fibers. The main portion of the dorsal spino-cerebellar tract is turned in an oblique direction about to pass into a dorsal position, from which it ultimately enters the restiform body. The ventral spino- thalamic tract passes dorsal to the olive, while the tract of Helweg is no longer discernible in the cross section. Along the outer margin of the inferior olive is a thick Ijundle of fibers running an oblique or horizontal course. This fasciculus constitutes the vellus oliva infenoris. The intermediate zone presents an area dorsal to the olive known as the retro-olivary -portion of the reticular formation. In this are the spino-thalamic, the rubro-spinal and the lateral Deitero-spinal tracts, as well as the formatio reticularis alba. The region formerly occupied by the juxtagriseal portion of the lateral white column now contains the formatio reticularis grisea. Many arcuate fibers cross through the intermediate and juxtagriseal zones of the lateral white column. These fibers finally enter the mesial fillet of the opposite side. Their presence gives the cross section the appearance of alternating stripes of graj' and white matter. 3. The ventral white column consists of the collected mass of the pyramidal fibers constituting the pyramids, and the collection of fibers extending from the dorsal aspect of the pyramids to the ventral surface of the central gray matter, the mesial fillet. The mesial fillet has as its lateral boundary upon either side the medial ventral accessory olive (paroliva medio-ventralis). The line along which the two fillets are in juxtaposition is marked by an area of thickened white matter constituting the raphe. 4. New Elements in the White Matter. Several new elements have made their appearance, of which the most important is the central tegmental tract. This forms part of the vellus olivje inferioris. It is found upon the peripheral surface of the inferior olive. The decussation of the fillet has already been observed in the next lower section, where tlie crossing was accomplished by a compact l)undlc of decussating fibers. At this level, the decussation con- sists of more loosely arranged bmidles of fillers forming the fibne arcuatcB interna'. Tliesc fibers arise in the nucleus cuneatus and nucleus gracilis, sweep forward in large arcs and cross the median line to enter the median fillet. The fasciculi comitantes trigcmini are still present in a position mesial to the sutistantia gelatinosa, and a small bundle ventral to these accompany- ing fasciculi indicates the fasciculus pyramidalis aberrans of Pick. The fibree arcuatw externa' vcntrales extend along the latcro-ventral surface, while the fihrw arcuatw externw dorsides encircle the dorsal surface of the medulla. Emergent Root Fibers. Emergent root fibers of the hypoglossal nerve arise in the nucleus of that nerve and make their way forward. Some of these fibers are in clo.se relation with the olive and emerge from the preolivary sulcus. Emergent root fibers arising in the nucleus anil)iguus of the vagus nerve follow a course similar to those of the spinal accessory nerve, first extending inward and backward, then coming into proximity with the dor- sal vagal nucleus, and finally turning by a sharp bend outward to emerge THE MEDULLA OBLONGATA 303 in the postolivary sulcus. This circuitous route of tlie emergent fibers of the eleventh and tenth nerves is a characteristic common to the nerves cf this group. Fissures. The ventro-median fissure is much more shallow than is the case in the next lower level, due to the interposition of the fillet between 304 FORM AND Fl'XC'TIONS OF THE CENTRAL NERVOUS SYSTEM i the central gray matter and the ventral surface of the medulla. The dorso- median fissure has lieconu^ a wid'c cleft and is about to he replaced by the opening which forms the fourth ventricle. CHAPTER XVII THE MEDULLA OBLONGATA INTERNAL STRUCTURE AND HISTOLOGY OF THE MEDULLA Changes in the Gray and White Matter at the Level through THE Middle of the Inferior Olive. Changes in the Gray Matter. 1. The ventral gray column as well as the lateral gray column is not repre- sented in this level. 2. The formatio reticularis presents its two divisions, the formatio reti- cularis grisea and the forynatio reticularis alba. 3. The dorsal gray column still presents the substantia gelatinosa which bears its constant relation to the descending root of the trigeminal nerve. 4. The cetitral gray matter has achieved its complete dorsal migration and has extended itself to form the floor of the fourth ventricle. The central canal has opened widely. Its ventral surface forms the floor of the ventricle, while its roof -plate, now much attenuated, and adherent to the pia mater, forms the chorioid plexus of the fourth ventricle. The ventricle appears as a triangular space bounded ventrally by the central gray matter and dorsally by the chorioid plexus. The surface of the central gray matter is thrown into several elevations which project into the ventricle; one of these is a mesial protuberance separated from a lateral protuberance by means of a sulcus. This sulcus is the remnant of the sulcus limitans and dehmits the basal from the alar plate. All of the floor of the ventricle lying mesial to the sulcus limitans is devoted to motor activities, while that portion of the floor lateral to the sulcus is designed for sensoiy activities. The special structures in the central gray matter are the nucleus hypo- glossi, dorsal to which is the nucleus intercalaris of Staderini. Dorso-mesial to tlie hypoglossal nucleus is a collection of fine fibers forming the fasciculus longitudinalis dorsalis of Schiitz. Beneath the sulcus limitans is the nu- cleus dor.salis vagi, made up of large motor cells and many smaller nerve cells. Lateral to the dorsal vagal nucleus is a group of small cells in con- nection with a well-defined fasciculus of nerve fibers. These nerve cells constitute the nucleus fasciculus soUtarius, while the bundle of nerve fibers is the fasciculus soUtarius itself. Lateral to the nucleus solitarius is a tri- angular field of gray matter containing cells of medium size; this is the nucleus vestibularis triangularis descendens, one of the receiving centers for the vestibular division of the eighth nerve. Occupying a dorso-lateral posi- tion, a special prolongation of the central graj' matter produces a prominence known as the tuberculuni acousticum. This is the dorsal acoustic nucleus in 20 305 30y ependymal cells, beneath which is a thin stratum of gray matter containing nerve cells of the smallest size. This is the hypependymal layer. 5. A'ew Elements in. the Gray Mntter. In addition to the nuclei men- tioned in connection with the floor of the fourth ventricle, a large group of cells appears ventro-mesial to the hypoglossal nucleus. This is the nucleus prepositus of Roller. A small nucleus has made its appearance at this level dorsal to the nucleus ambiguus and ventro-mesial to the substantia gelatin- osa. This is the nucleus salivaturiu.^ inferior. Another collection of medium .sized motor elements, identified Ia' Dejerinc in connection with the control of the intrinsic mustdes of the eye, is tlie nucleus cllio-niedullaris situated in the reticular formation \'entral to the dorsal nucleus of the vagus. This nucleus innervates the dilator fibers of the iris, the ciliary muscle and Hor- ner's muscles of the upper lid and orbit. Injury or disease of this region pro- duces among other symptoms, enophthalmia, myosis, inequality of the pupils and slight drooping of the upper eyelid. The nucleus fasciculus solitarius is connected with the gustatorj' sense, while the tuljcrculum acousticum constituting the dorsal acoustic nucleus, is related to the coclilear division of the eighth nerve, and thus with the sense of hearing. The nucleus gracilis at tliis le^'el has disappeared and the nucleus cune- atus is much reduced in size. It occupies a position lateral to the nucleus vestibularis triangularis descendcns and mesial to the fibers which constitute the inferior cerebellar peduncle (corpus restiforrnej. The inferior olive ap- pears as a convoluted Ijaiid of graj' matter having a fundus and a hilus. The fundus contains a mass of white fibers which enter and leave at the hilus. The nucleus ar(;iformis has increased in size and occupies its usual position mesial to the pyramids. The nucleus amliiguus has enlarged, and the nucleus reticularis lateralis is present though much reduced in size. Changes in the While Mailer. 1. The dorsal white column at this level has disappeared, due to the opening of the fourth ventricle and the general ventral shift of all the elements which formerly occupied this position in tlie spmal cord. 2. The lateral white column shows considerable rearrangement, due especially to the dorsal shift which has taken place in the dorsal spino- cerebellar tract. This tract, together with fibers coming from the inferior olives, the nucleus cuneatus and the nucleus gracilis, has formed a massive bundle known as the corpus restiforme or inferior cerebellar peduncle, which lies ventral to the tuberculum acousticum and lateral to the remains of the nucleus cuneatus. The ventral spino-cerebellar tract holds its usual position in the circumferential zone, interposing itself between the inferior olive and the restiform body. Along the vcntro-lateral aspect of the inferior ohve is a well-marked descending tract constituting the central tegmental THE MEDULLA OBLONGATA 309 tract of Bechterew. It is incorporated with many fibers which form the vcUus olivoe inferioris. The intermediate zone of the lateral white column is reduced in size and contains the descending spinal root of the trigeminal nerve, the spino- thalamic and rubro-spinal tracts, and the formatio reticularis alba. The juxtagriseal portion of the lateral white column consists of the forma- tio reticularis alba. 3. The ve7^tral white column extends from the- ventral surface of the me- dulla as far back as the ventral surface of the central gray matter. The ventralmost element is the pyrnmul, dorsal to which is the mesial fillet. The dorsalmost element in the ventral white column is the fasciculus longi- tudinalis posterior. The hilus of either olive is directed dorso-mcsially, and from it emerge many fibers which arise in the olive. These fibers pass directly toward the median hne, which they cross, and after sweeping dorso-laterally, they ultimately enter the restiform body on the opposite side. This con- stitutes the inferior olivary decussation. It establishes a contralateral con- nection between the inferior olive and the cerebellum. Many fibers arising in the substantia gelatinosa make their way into the ventral white column, crossing the mid-line and entering into the formation of an ascending tract connected with the trigeminal nerve. This tract, in all probability, is part of the secondary pathway for the fifth nerve, and represents the avenue of conduction over which impulses from the surfaces of the head and face pass on their way to the cerebral cortex. Scattered among the dorsal fibers of the fasciculus longitudinahs posterior are some large motor cells which make up the nucleus of Roller. 4. New Elements in the White Matter. The appearance at this level of the fasciculus longitudinahs posterior as a discrete bundle is the most prominent addition to the white substance. This fasciculus represents an intersegmental association tract whose purpose is the coordination of the several groups of eye muscles, and the correlation of such movements with the reactions of the vestibular mechanism. The fasciculus sohtarius is especiallj' prominent and occupies a position ventro-lateral to the dorsal vagal nucleus. The inferior olivary decussation is also a feature at this level as well as the decussation of fibers arising in the substantia gelatinosa and taking part in the formation of the secondary trigeminal pathway. Emergent crnd Entrant Root Fibers. The emergent root fibers of the hypoglossal and the vagus nerves are seen at this level. The vagal fibers are joined by afferent elements coming from the vagal ganglia. These afl'erent fibers make their way to the dorsal vagal nucleus, which acts as a sensory relay station in the pathway of this nerve. Fissures. The ventro-median fissure, although conspicuous on the sur- face, due to the prominence of the pyramids which rise upon either side of it, has become less deep because of the inferior olivarj' decussation and the position of the mesial fillet. The dorso-median fissure no longer exists. The columns bounding it have become divergent in such a manner as to bring the central gra}- matter into the floor of the fourth ventricle. 310 form and functions of the central nervous system Changes in the Arrangement of the Gray and White Matter AT the Cephalic Limit of the Inferior Olive. Changes in the Gray Matter. All seniblanco of (1) the ventral gray column and (2) the lateral gray column is lost, and no structure in any way similar to these elements may be discerned. The remnant of (3) the dorsal gray column is repre- sented in a much reduced substantia gelatinosa which occupies a position mesial to the restiform body and lateral to the formatio reticularis alba. 4. The central gray matter forms the floor of the fourth ventricle which at this point has its greatest transverse extent, reaching from one lateral recess to the other. The groups of cells entering into the central gray matter are as follows : (rt) The nucleus prepo^iiltis hupoglosKi, a collection of medium-sized stichochrome cells situated below ib) the iiiicJeus fasciculus teretis, a collec- tion of small nerve cells. Lateral to the nucleus prepositus is (c) the nucleus vestibularis triangularis connected with the vestibular mechanism. Ven- tral to this nucleus is (d) the nucleus glossopharyngei, made up of large motor elements interspersed among a much greater number of small cells of the sensory type. Lateral to the triangular vestibular nucleus is (e) the nucleus (lorsalis acoustici, in a position subjacent to the floor of the fourth ventricle and dorsal to the inferior cerebellar peduncle. Ventral to the dorsal acoustic nucleus and mesial to the inferior cerebellar peduncle is a large nucleus containing large cells of the motor type. This is (/) the nucleus of Deiters or the 7i:ucleits magno-ccllularis restibularis. Interposed I)etween the nucleus glossophar3mgei and Deiters' nucleus is a massive bundle of coarse fibers which follow a descending course and constitute the descending vestibular root. The floor of the ventricle is covered by ependvmal cells, beneath which in many cases the secondary fibers arising in the dorsal and ventral acoustic nuclei cross toward the niidhne where they undergo decussation. These fibers are the stricr acousticcr. The nucleus andjiguus has disappeared, but occupying its usual position, midway between the inferior olive and the substantia gelatinosa, is the caudal extremity of the large motor nucleus of the facial nerve, the nucleus facialis. The nucleus arciformis has increased in size, in some places making its way in among the pyramidal fibers and extending well into the depth of the ventro-median fissure. Another nucleus seen at this level extends along the mesial aspect of the fasciculus longitudiaalis posterior and the mesial fillet. This is the nucleus ventralis inferior. The most important new element at this level is Deiters' nuclcux^ which has already been defined as the nucleus magno-cellularis ^-estibularis. The reticular formation shows a marked increase in the size of the formatio reticularis alba with a corresponding reduction in the size of the formatio reticularis grisea. Changes in the Wliite Matter. Both dorsal cohinins have disappeared and the lateral columns have been subjected to much alteration. In the circumferential zone, the restiform body or inferior cerebellar peduncle forms the most dorsal element. "Wntral to it is the ventral spino-cerebellar THE MEDULLA OBLONGATA 311 312 FORM AND INUNCTIONS OF THE CENTRAL NERVOUS SYSTEM tract, in front of which is situated the central tegmental tract and the vellus olivse inferioris. The intermediate zone is made up of the spinal root of the trigeminal nerve, the rubro-spinal and the spino-thalamic tracts. Each of these occupies its usual position. A number of horizontally crossing fibers pass through the intermediate zone; they arise in the olives and are making their way from this source to the inferior cerebellar peduncle. The juxtagri- seal portion of the lateral white column consists of the formatio reticularis alba. The ventral white column contains the pyramid, dorsal to which in the order mentioned are the collected bundle of the fillet, the fasciculus pre- dorsalis and the fasciculus longitudinalis posterior. A number of external arcuate fibers dip into the ventro-median sulcus and give the raphe increased prominence. These fibers imdergo decussation in the midline, from which point they may be traced in either direction to the inferior cerebellar pe- duncle. Some fibers from Deiter's nucleus and from the vestibular triangular nucleus pass from these sources to the raph^ where they cross and enter into the formation of the opposite fasciculus longitudinalis posterior. Emergent and Entrant Rout Fibers. A few of the most cephalic fibers of the hypoglossal nerve are seen emerging from the preolivary sulcus at this level. Fibers arising in the nucleus glossopharyngei proceed outward to the postohvary sulcus, where they escape and are joined by afferent sensory elements making their way to the nucleus fasciculus solitarius or the dorsal sensory nucleus of the glossophar3'ngeal nerve. The entering fibers of the cochlear division of the eighth nerve come into relation with the ven- tral accessor}' acoustic nucleus; passing dorsally and mesially the}' enter into connection with the dorsal acoustic nucleus. Fissures. The ventro-median fissure is again prominent because of the large size of the pyramids and the increased dimensions of the arciform nuclei. The two lateral recesses project laterally from the floor of the fourth ventricle and come into relation with the ninth and tenth nerves laterally, and with the seventh and eighth nerves situated ceplialad to them. Summary of the Changes which Occur in the Arrangement of the Gray and White Matter of the Medulla Oblongata. The changes which take place in the gray matter occasion the most marked alterations in the ventral and lateral gra,y columns, both of which ultimately disappear and are replaced by structures which are not present in the spinal cord. The lateral migration of the dorsal gray column and its marked increase in size, together with its relation to the descending spinal tract of the tri- geminal nerve, and the loss of its neck and body, constitute other conspicuous alterations in the gray matter. The migration which has occasioned greatest differences in the appearance between sections of the medulla and the spinal cord is that which affects the central gray matter, gradually forcing this portion of the gray substance into a more dorsal position, until finally it participates in the formation of the floor of the fourth ventricle. In addition to this migration dorsally there is a pronounced increase THE MEDULLA OBLONGATA 313 in the size of the central gray matter, which gives it new significance in the administration of splanchnic functions. In consequence of this increase m the central gray matter, provision is made for the several nuclei of the vagus, of the glossopharyngeus and of the hypoglossal nerves, as well as the vestibular and cochlear divisions of the eighth nerve. The expansion of the formatio reticularis is of much moment in the formation of the internal structure of the medulla, especially the formatio reticularis grisea. This portion of gray matter is believed to form one of the most important nuclei controUing respiratory activity. The Appearance of New Elements in the Gray Matter. A number of collections of nerve cells not observed in the spinal cord are found at different levels of the medulla oblongata. Certain of these new cell groups require particular attention : 1. The jutclei of the dorsal column, the nucleus cuneatus and nucleus gracilis. These new elements in the gray matter cause the pronounced changes in the dorsal white column which, as previously explained, in- troduce the means of relaying sensory impulses on their way to the cere- bral cortex. 2. The dorsal nucleus of the vagus, the nucleus dorsalis vagi, consists of a motor and a .sensory portion. It serves the vital processes which regulate cardiac action, respiration and gastro-intestinal activity. 3. The nucleus amhiguus contributes fibers to the formation of the vagus, probabl.y in the interest of controlling the larynx. 4. The dorsal nucleus of the glossopharyngeal nerve consists of motor and sensory elements. The nucleus fasciculus solitarius, is involved in the forma- tion of the secondary pathwaj^s for the transmission of gustatory impres- sions from the tongue. 5. The hypoglossal nucleus gives rise to the nerve supplying the intrinsic muscles of the tongue. It is the only somatic motor nerve arising in the me- dulla oblongata. All other motor elements derived from the medulla belong to the splanchnic motor group. 6. The nucleus of Roller is situated upon either side of the raph^ ventral to the nucleus of the hypoglossal nerve. To it has been attributed participa- tion in the control of respiratory functions. 7. The inferior olive, with its several accessory olivary nuclei, whose function is still in doubt, seems to be related to the coordinative control of the head and eye movements. 8. The nucleus arcifonnis serves as a relay in the course of the external arcuate fibers, probably affording an accessorj' afferent connection between the muscles and the cerebellum by way of the inferior cerebellar peduncle. 9. Deiters' nucleus acts as a center for equilibratorv control of the muscles in their relation to the semicircular canals, utricle and saccule. 10. The triangular vestibular nucleus serves in a capacit}^ similar to that of Deiters' nucleus. 11. The ventral and dorsal acoustic nuclei act as relay stations in the formation of the secondary tracts forming the pathway for hearing. 314 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM 12. The facial nucleus controls the muscles of facial expression. The caudal extremity of this nucleus in most specimens appears in the cephalic portion of the medulla. Rearrangement of the Wpiite Matter in the Medulla Oblongata. The white matter of the medulla oblongata is notable because of the decus- sations which take place within it. Six of these decussations occur and are of major importance: 1. The pyrarnidal decussation, which takes place at the caudal extremity of the medulla and serves to effect a contralateral connection between the cerebral motor cortex of one side and the somatic musculature of the opposite side of the body. 2. The decussation of the fillet is accomplished bj^ the crossing of internal arcuate fibers. It makes possible the contralateral connection between the receptors of one side of the l;)ody and the opposite side of the cerebral sensory cortex. 3. The inferior oUvarij decussaliou., which brings the inferior olive of one side into relation with the cerebellar structures of the opposite side through the inferior cerebellar peduncle. 4. The decussation of the external arcuate fibers, which brings the nucleus cuneatus ami tlic nucleus gracilis into relation with the opposite side of the cerebellum through the inferior cerebellar peduncle. 5. The decussation of trigeminal fibers, which determines a cross connec- tion lictween areas innervated by the trigeminal nerve and the opposite side of the cereliral sensory cortex. 6. The derusiiiition of fibers front Deiters' nucleus to the fasciculus longi- tudinalis postrrior. This determines a partial contralateral connection in the Deitero-spmal tracts as well as between the nucleus of Deiters and the nuclei guiding the eye muscles. Rearrangement of the Lateral White Column. In the cephalic portion of the medulla oblongata the lateral white columns are so arranged that the inferior cerelx'llar peduncle becomes the most dorsal element of the circumferential zone. Ventral to this peduncle is the ventral spino-cerebellar tract. The olivo-spinal tract of Hehveg has terminated in the inferior olive, and its former place is now occupied Ijj' the central tegmental tract. The inferior cerel)ellar peduncle consists of the dorsal spino-cerebellar tract, 1() which are add(>d fibers from the inferior olive as well as from the nucleus cuneatus and nucleus gracilis. The fibrae arcuatai externae ventrales encircle the lateral circumference of the medulla for a consideraljle distance in the mid-olivary region. The main differences between the circumferential zone of the medulla oblongata at this level and that of the spinal cord consist of the dorsal shift of the dorsal spino-cerebellar tract to enter the restiforni liody, the disapjx^^arance of the tract of Helweg and the assumption by the descending root of the fifth nerve of a position in the intermediate zone. The intermediate zone of the lateral white column is much smaller than THE MEDULLA OBLONGATA 315 in the spinal cord. It contains the spinal root of the trigeminal nerve with its fasciculi comitantes, also the fasciculus pyramidalis aberrans of Pick and the formatio reticularis alba. In the cephalic portion of the medulla no fibers of the crossed pyramidal tract occupy this position. Ventral to the substantia gelatinosa and dorsal to the inferior olive lie the spino-thalcmiic and rubrospinal tracts. The juxtagriseal portion of the lateral white columns consists largely of the formatio reticularis grisea, which belongs more properly to the gray substance. It undoubtedly has the significance of an important interseg- mental association system whose chief function is connected with respiration. Rearrangement of the Ventral White Column. This column in the medulla oblongata is much more extensive than the corresponding region in the spinal cord. It extends from the ventral periphery to the ventral margin of the central gray matter and has, as its lateral boundaries, the inferior olives and the emergent fibers of the h3'poglossal nerves. In it are the fibers constituting the pyramids, dorsal to which are fibers which make up the mesial fillet, the fasciculus predorsalis and the fasciculus longitudinalis posterior. In connection with the latter fasciculus, there are some fibers which eventually come into relation with Deiters' nucleus, forming the ven- tral Deitero-spinal tract, and also fibers of the tecto-spinal tract. The essential changes in the arrangement of the white matter of the medulla oblongata depend upon the increased prominence of the ventral white column, which contains not only the pathway for volitional control over the muscles, but also part of the conduction system which serves to con- vey sensory impressions from the body to the cerebral cortex and has its spinal representation in the dorsal white column. This shift from the dorsal white column of the spinal cord to the ventral white column of the medulla oblongata is so complete that nothing remains in the cephahc portion of the bulb of the formerly important groups of fibers constituting the columns of Goll and Burdach. Quite as important is the shift of the pathway for voli- tional control from the lateral white column, which it occupies in the spinal cord, into the ventral column of the medulla. One feature concerning the lateral white column needs emphasis, namely, the consistency with which the rubro-spinal and spino-thalaniic tracts adhere to their usual spinal cord positions in making their way through this portion of the brain. The same distinction also applies to the ventral spino-cerebellar tract and the lateral Deitero-spinal tract. CHAPTEE XVIII THE AIEDULLA OBLOXGATA FUNCTIONAL SIGNIFICANCE OF THE MEDULLA The Functions of the Gray Matter. The functions of the graj' matter of the medulla oljlongata may be classified with reference to the com- ponents through which they act. The chief function of this portion of the brain is represented by the splanchnic autonomy which the medulla holds over the vital processes of respiration, cardiac action, deglutition and intes- tinal activity. This autonomy is expressed in the activities of the splanchnic motor and splanchnic sensory components. In addition to these splanchnic activities, the gray matter of the medulla acts as a relay station for several qualities of somatic sensiljility and mediates influences which control the action of certain somatic muscles. Splanchnic Motor Functions of the Medulla. Through the dorsal motor nucleus of the vagus and glossopharj'ngeus nerves, the medulla in- nervates many glandular effectors and im'oluntarj- muscles. Among these motor and glandular effectors are: 1. Tlie muscles of the soft palate. 2. The constrictors of the pharynx. 3. The muscles of the esophagus. 4. The muscles of the stomach. 5. The muscles of the intestines and part of the colon as far as the de- scending colon. 6. The musculature of tlie lironchial tree and trachea. 7. The musculature of the heart. It also innervates the salivary glands through the inferior sahvary nucleus as well as exerting an effector influence over the glycogenic activity of the liver and the secretions of the pancreas. Through the vagus nerve the medulla aids in activating the glands of the stomach and intestines. The innervation of the fauces and phai-ynx is effected by the glosso- pharyngeal nerve, while the lower portions of the respiratorjr and gut tracts are regulated by the vagus. The medulla ol.)longata controls the muscular activities of the larynx, to which impulses are supplied by the nucleus ambiguus. It also in part controls the facial muscles, through the motor nucleus of the facial nerve, which is the final common pathway for the mus- culature of expression and the platysma myoides muscle. Splanchnic Sensory Functions of the Medulla. Through the sensory nuclei of the vagus and glossopharyngeus nerves, the medulla aft'ords the following areas their splanchnic sensory supply: :5l(j THE MEDULLA OBLONGATA 317 Inferior Olive ephalic Ven- .ricular Level of the Medulla Pvrdmidal Tract Central Gray Matter Mesial Fillet Nucleus Gracilis Ventricular Level of theMeduMa Nucleus Cuneatu5 Reticular Formation nfravenfricular Level of the Medulla Fig Py ram Ida Decussation Inferior Level offhe Pyramido Decussation in the Medulla inferior Olive pYramidal Tract Superior Level offhe PYiamidal Decusiaion nfhe Medulla V'enfral Crav Column Dorsal Spina-cere- bellar Tract ventral Spmo-cere- Dellar Trac: Lateral Deiteio- Spmal Tract 255. — The pyra- midal tract witli its decussation in the medulla. It represents tlie medullary divi- sion of the pallio- spinal pathway, from the giant pyramidal cells of the precentral cortex to the ven- tral gray column cells. This tract serves for the con- duction of impul- ses of volitional control over the somatic muscula- ture. 318 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM 1. Part of the dura mater in the region of the sinus transversus. 2. The soft palate. .3. The postei'ior third of the tongue with the special sense of taste. In this region it also sup])Iies the mucosa of the Eustachian tube, and through Jacobson's branch of the glossopharyngeal nerve, the tjmipanic cavity, the fenesti'a ovahs, the fenestra rotunda, and the mucosa of tlie mastoid cells. 4. The jjharynx and epiglottis. 5. The laryn.x. 6. The trachea. 7. The respiratory mucosa. 8. The mucosa of the esophagus. 9. The mucosa of the stomach. 10. The mucosa of the duodenum, jejunum and ileum. 11. The mucosa of the bile ducts. 12. The mucosa of the ascending and transverse colon. 13. The heart and pericardium. Concerning the supply of the sense of taste to the posterior third of the tongue, the arch of the palate and the uvula, there is some difference of opinion. According to certain authorities, the trigeminus nerve supphes the sensor}' elcmient, and the ninth nerve the special taste innervation. According to others, the glossopharyngeal nerve is wholly sensory, while the trigeminus is the taste nerve; some believe that each of these two nerves has a dual function, in part sensory and in part taste. The central receiving station for the sense of taste is the nucleus fasciculus solitarius. The root fibers entering into connection with this nucleus arise chiefly in the seventh and ninth nerves, although the tenth nerve may make a small contribution to it. The medulla innervates the anterior two-thirds of the tongue with special splanchnic sensory fibers of taste through the chorda tympani, the sensory division of tlie facial riei'vc. Somatic Motor Functions of the Medulla Oblongata. Through the hypoglossal nerve, the medulla supplies all of the intrinsic muscles of the tongue. These muscles are derived from myotomes and hence the tongue is to be regarded as belonging to the somatic motor system. By means of the inferior olive, the medulla furnishes an important center for the synergic control of the eye and head movements together. The functional significance of the inferior ohvary body is not clear at present. Bechterew regards it as a center for static eciuihlsrium. This sup- position does not seem to accord well with the facts. The olive reaches its highest development in those animals requiring the most exact cooperative coordination lietween eye movements and movements of the head. The anatomical connections of the olive lead to the belief that its function is the coordination of these movements. Its connection with the cerebellum through the olivo-cerebellar fibers, with the nuclei of the oculomotor ap- paratus through the central tegmental tract and with the upper cervical segments of the spinal cord through the tract of Helweg, seems to point to THE MEDULLA OBLONGATA 319 a mechanism which is especially well adapted to bring into relation move- ments of the eyes and of the head. The Somatic Sensory Functions of the Medulla Oblongata. The me- dulla oblongata serves as the chief relay station in the pathway of impulses arising in the inner ear and proceeding to the auditory area of the brain to serve the purposes of audition. These fibers develop in connection with the cochlear portion of tlie eighth nerve. The more primitive division of the eighth nerve, that which is connected with the semicircular canals, the utri- cle and saccule, also receives a relay in the medulla. This relay connects with certain areas of the brain involved in equilibratorj^ control. Accord- ing to some authorities, the fibers arising in tire organs of the vestibular system belong to the proprioceptive system, as do also the fibers which arise in the muscles, joints and bones. There can be no objection to considering the vestibular fibers as integral parts of the proprioceptive system, provided it is recognized that their organs are geneticallj^ related to the ectoderm. The end-organs of the muscles, joints and bones, on the other hand, are related to the mesoderm. The medulla, by means of the nucleus cuneatus, the nucleus gracilis and the substantia gelatinosa, affords relays for the discriminative types of sensibility coming from the leg and lower trunk, from the arm and upper trunk, from the back of the head and face. It is probable that through the relay of the substantia gelatinosa all types of sensory impulses are transmitted to the cerebral cortex. A small aberrant branch of the vagus nerve supphes a cutaneous area in the external ear immediately surrounding the external auditory canal. This innervation is effected through Arnold's nerve. Simple Reflexes Mediated through the Medulla Oblongata. The Coughing Reflex. This reflex may be determined by stimulation of the mucous membrane of the pharynx, of the larynx, of the trachea, of the bronchial tree or of the external auditory canal. The afferent impulses are conveyed by branches of the vagus nerve. They reach the dorsal nucleus of the vagus, and are transmitted to the respiratory nucleus of the meduUa which occasions a forceful expiratory effort preceded by a deep inspiration. The Swallowing Reflex. This reflex is occasioned by mechanical stimula- tion of the wall of the pharynx, and is activated through branches of the vagus and glossopharyngeal nerves. The motor center of the reflex is in the dorsal vago-glossopharyngeal nucleus. Section of the glossopharyngeal nerve causes the disappearance of the swallowing reflex. Vomiti?ig or Regurgitation Reflex. This reflex may be determined by abnormal stimuh in the region of the cardia of the stomach, in the wall of the pharynx, in the gastro-intestinal tract, or in the internal ear. The af- ferent arm of the reflex is furnished by the vagus and glossopharyngeal nerves. The motor center is in the dorsal motor nucleus of the vagus, a special subdivision of which is sometimes spoken of as the vomiting center. The efferent arm of the reflex is furnished by the vagus nerve together with the somatic nerves to the abdominal wall and diaphragm. The Salwartj Reflex. This reflex may be determined by stimulation of 320 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM nferior Cerebellar Peduncle RubrosDinal Tract Mesial nilet Inferior Olive CephalicVentricular Level of Medulla Pyramid central GraYMatler Rubrospinal Tigct Caudal Ventricular Level Q-f Medulla Mesial nilet ■Inferior Olive PYramid NucieusGracilis NucleusCuneatus Central Giav Matter Rubrospinal Tiact SpinothalamicTract .nfraventricular Level of Medulla PYl'amid Nucleus Gracilis NucleusCuneatus RuDrospinal Tract Central G)av fatter Fh Cephalic Level of Pyra- midal Decussation in Medulla ■Rubrospinal Tract Caudal Level of Pyi'a- midal Decussation in Medulla final Co^ri'DnPaltwav . 25(3. — The rubro-spinal tract passing through the medulla and repre- senting the medullary division of the cere- bfUo-rubro-spinal path- \yay for the conduction of impulses necessary to synergic control of the somatic muscles. THE MEDULLA OBLONGATA 321 the mucous membrane of the vestibule of the mouth, of the Ups, or of the general mucosa of the oral cavity l)y chemical, mechanical, or other gusta- tory stimuli. Stimulation of the chorda tympani, of the oral distribution of the trigeminus or of the glossopharyngeal area, will cause the passage of afferent impulses to the nucleus salivatorius inferior in the medulla, and determine effector impulses activating the salivary glands. The Sneezing Reflex. This reflex may be determined bj^ afferent im- pulses received from the mucous membrane of the nasal cavity by way of the trigeminal nerve. When transmitted to the respiratorj^ nucleus in the medulla they activate a forceful expiratory effort forcing the air through the nasal passages under considerable pressure. The sucking reflex of the new-born maj' be regarded as a simple reflex, inasmuch as it is determined by the presence of an object in the mouth of the infant, thus stimulating the trigeminal and glossopharyngeal nerves to transmit sensory impulses to the medulla, from which arise motor im- pulses distributed through the hypoglossal, glossopharyngeal, and facial nerves, bringing the respiratory centers into play at the same time. In later life the reflex is conditioned by control from higher divisions of the brain. The Medulla in its Relations to Special Functions. The medulla oblongata has autonomous control over certain vital functions, chief among them being those of respiration, cardiac activitj^ ingestion, de- glutition and digestion of food, circulation, metabohsm and secretion. The IMedulla Oblongata in its Relation to Respiration. In considering the relation of the medulla oblongata to the function of respira- tion, it is not proposed to discuss the physiology of this mechanism as a whole, but rather the role which the myelencephalon plays in it. The Muscle Groups Active in the Respiratory Mechanism. The respira- tory mechanism brings into action certain muscular groups of the body. These may be classified as (1) the principal groups, (2) the ordinary ac- cessory groups, and (3) the extraordinary accessory groups. In extreme emergency, it is probable that few muscles of the Ijody are exempt from participation in the respiratory effort. 1. The Principal Muscle Groups Active in the Resprratonj Mechanism. (a) The chief muscle acting in respiration is the diaphragm, which is supphed by the phrenic nerve, the latter arising in the third, fourth and fifth cervical segments of the spinal cord. (b) The external intercostal muscles and the intercartilaginous muscles, which are suppUed by the intercostal nerves arising in the thoracic segments of the spinal cord, from the first to the twelfth inclusive. (c) The long and short levator of the muscles of the ribs, supphed by the dorsal branches of the intercostal nerves. These groups of muscles act in ordinary inspiration, while in orchnary expiration there is no actual muscular contraction, since the elasticity of the tissues of the thoracic basket, together with that of the lungs and the abdom- inal muscles, determines the expiratory movement. 21 .322 FORM AND FrNCTIONS OF THE CENTRAL NERVOUS SYSTEM 2. The Ordinarii Accessory Muscles Active in the Rcspiratejry Mechanism, (a) The scrratus posticus superior muscle, supplied by the dorsahs scapuhe nerve, which arises in the cervical .segnicnts of the spinal cord. ill) The slerno-cleido-niastoid muscle, supplied by the spinal accessory nerve. (f) The trapezius muscle, supplied Ijy the spinal accessory nerve. {(l) The ]-homboid muscles, supplied by the nerve to the rhomboids which arises in the cervical segments of the spinal cord. (e) The pect oralis minor muscle, supplied bj' the internal anterior thoracic nerve. Certain muscle groups serve to assist the respiratory act by increaising the capacity of the passages admitting the air. These are: (a) The depressors of tlie larynx, thesterno-hyoidand the sterno-thyroid muscles, supplied by the descendens hypoglossi nerve. (b) The crico-arytenoid postei'ior and the thyro-arytenoid separate the vocal cords. These muscles are supplied by the recurrent laryngeal nerve, a branch of the vagus. (c) The depressors of tlie lower jaw, supplied by the trigeminal, facial and hypoglossal nerves. (d) The depressors of the tongue, supplied by the hypoglossal nerve and the pharyngeal plexus. (c) The levator palati, supplied l>x the pharyngeal plexus. (/) The azygos uvulae, supplied by the pharyngeal plexus. (g) The dilator narium anterior and posterior, supplied by the facial nerve. (h) The levator alae nasi, supplietl liy the facial nerve. In deep expiration the alidoniinal muscles take part by compressing the aljdomen. These muscles are supplied by the abdominal branches of the eighth to the twelfth intercostal nerves inclusive. The internal intercostal muscles also act in deep inspiration to increase the capacity of the thoracic cavity. 3. Extraoriluianj Aecvssunj (jroiips Active in Respiration. In labored and extreme respiratory efl'ort, the entire musculature of the body may act. This is seen in cases of suffocation, when the whole body is thrown into convulsive movement in the struggle to gain aii'. Respiratory Coordinating Center of the Medulla Oblongata. The fact that such a wide range of the muscles nuiy come into action to meet the rerpiirements of respiration, in'. Tliesc tracts serve for the con- duction of im- pulses from the somatic muscles to the cerebel- lum. The tracts form the affer- ent arms of reflex arcs whose center is in the cere- bellum. They are part of the me- chanism active in synergic control of the muscles. THE MEDULLA OBLONGATA 33/ 4. The spino-cerebellar pathway which undergores a partial crossing l.iy means of the ventral and dorsal external arcuate fibers. 5. The trigeminal pathwaj^, the decussation of which jjrovides a com- plete crossing for all types of sensibility from the regions of the head, face and cavities of the head. 6. The Deiteral pathway, the decussation of which consists of a partial crossing of the fibers arising in Deiters' nucleus and entering either the fas- ciculus longitudinalis posterior or the ventral Deitero-spinal tract. Summary of the Functions of the Medulla Oblongata. The functions of the medulla oblongata may be summarized briefly as follows: The gray matter of the medulla represents a dominant autonomy over the A'ital processes of life. It mediates an essential control over respiration, cardiovascular activity, phonation, art'culation, deglutition, digestion, secretion and metabolism. It also acts as an important relay station for both divisions of the auditory nerve. The ivhite matter of the medulla represents the continuity in all of the major conduction paths which serve to maintain efficient relations between the receptors and effectors of the body. Not only is the medulla traversed by many of the most important afferent and efferent pathways of the nervous system, but it is also the site of decussation of several conduc- tion systems, notably the mesial fillet, Deitero-spinal, olivo-cerebellar and pyramidal tracts. CHAPTER XIX THE AIEDULLA OBLONGATA PRINCIPAL SYNDROMES OF THE MEDULLA In consequence of its marked rearrangements, it is impossible to de- scribe the sjmdromes of the medulla as those affecting the gray matter or the white matter separately. Usuallj^ some part of both of these elements is involved by the lesion. The syndromes of this part of the brain-stem are most conveniently designated bj' the chief structures implicated by the patho- logical process. This method will be employed in the following descriptions. Not all of the sjanptom-complexes which may arise in connection with disease of the medulla will be discussed, but rather those most illustrative of the functional possibilities in the light of anatomical relations. Syndrome of the Pyramidal Decussation. History. A young man, as the result of diving, rei- parts of the liody were normal. In the course of several days the right arm and left leg became rigid, and he suffered from a spastic paralysis in the parts affected. This condition, gradually improving, per- sisted for a year, when the patient died of pneumonia. Examination. Sonintic Motor Component. The idiodynamic control of the affected arm and leg was normal. The reflexes in the right arm were more active than the left arm, while the reflexes in the left leg not only showed an increase as comjiared with those of the right leg, but certain pathological reflexes were also present, as the Babinski, crossed periosteal, ankle and patellar clonus. The muscle tone of the right arm was increased to such a degree as to determine a malposition of the fingers, which were held in flexion, and of the forearm, which was drawn up with a slight degree of flexion at the elbow. There was an increase in tone of the left leg as com- pared with the tone of the right leg. At the time of the examination, there was a complete loss of volitional control in the right arm and left leg, the left ai'iii and right leg being normally under the control of the will. Synergic control 111 the affected iiarts C(juld not be determined Ijecause of the marked degrei^ of spastic paralysis. I'>[uilil)ratory control was normal in the un- affected parts, but could 110I lie estimated in the paralyzed meml.iers. All of the cranial nerves were noinial. The Somatic Seiivori/ Cunipoiie/it. This component showed no distur- bance in any type of somatic sensibility. 33.S THE MEDULLA OBLONGATA 339 The splanchnic motor and splanchnic sensory components likewise were normal. iNTEKFiiETATioN AND ANATOMICAL AxXALYSis. The sucldeu appearance of symptoms following an injury and attended by unconsciousness indicates the traumatic nature of the lesion which, in all probabihty, caused a hemor- rhage in the central nervous system. The evidence of the focus of the lesion points conclusively to involvement of the pyramidal tracts, and the only position m which these tracts could be simultaneously involved in such a way as to effect a paralysis of an arm and the opposite leg is in the pyramidal decussation at a level in which the arm fibers have already made their crossing and the leg fibers in the pyramidal system arc about to decussate. Fig. 263. — A. Syndrome of (the pyramidal derussation (hemiplegia cruciata or cros.sed hemiplegia). Red indicates an upper motor neurone paral\sis ■i\ith spasticity and abnormal reflexes. R. Cros.s section through tlie_ medulla at the level of the pyramidal decussation showing the location of the k'sion in hciiriphgin. cruaata involvement of crossed arm and uncrossed leg fibers ot pyramidal tract. The evidence of circtunscription of the lesion is to be found in the ab- sence of all other motor and sensory disorders, ihus limiting the area of involvement exclusively to the iiyramidal decussation. Diagnosis and Pathology. This condition is due to trauma affecting the pyramidal decussation, and probably giving rise to a hemorrhage m this part of the medulla. Nomenclature. This s}-ndrome is known as hcnuplcijm cntciatn or crossed hemiplegia. Variations. If the lesion is extensive enough to involve all the Inmdles of decussating fibers, the resulting paralysis is a spastic letraplegia, includ- ing all four extremities. 340 FOKM AND FT'XCTIOXS OF THF CEXTItAL NEKVOUS yVHTp; "HTfJM Summary. Tlie es.seiilial rliiiic;il fi'aim'fs oi Hus s>'j-)(lroiiic are: 1. Crossed lunniplegia, unolvin,'^- an arm and the opposite leg. 2. U|ipci' motor neurone type of pai'alysis ,\vith increased anrl pathological I'cfle.xes and increased muscle tone. 3. Idle appearance of abnormal asserialed moA'emenIs m the paralyzed riarts. 4. The ali-'ence of all sensory and s|)laii(-linic symptoms, and the ah- seiice of an\- symptoms referable to the ci'aiiial ner\-es. V\|^. 2(34. — ,1 ami B. S^yiidronic el' the ['y^nind ami liypnirlc;i.s.'pogIossaI tillers. Syndrome of the Pyramid and the Hypoglossal Nerve. IIistohy. A man fifty-three years old, wlhle at biisiin'.ss, was suddenly seized with a fainting .sjiell which lasted several minutes. I'pou regaining coii- sriousness, lie felt weak and cduM neither speak iiui' move his right ai'in (II' leg. After several days his spee(di returneil, altliDUgh he was conscious ol chfKculty in mo\dng his tongue. His right ariii and leg remained paralj'zed and gradually Ijecanie iigid. He remained m tliis general condition until the end of his life, wdiicli followed two ycais lati.'r iii consequence of a severe .-ipojilejdic seizure. THE MEDULIjA (JBLONGATA 34] Examination. The somatic motor cotiiponcnt showed a complete paraly- sis of the right arm and leg with a paralysis and atrophy of the left side of the tongue. The idiodynamic control of the right arm and leg was normal. The reflexes were all increased on this side of the body, the Babinski, the patellar and ankle clonus being present. The reflexes of the left side of the body were normal. Volitional control was lost on the right side, including the right arm and leg, while synergic and equilibratory control could not bo estimated on account of the extreme degree of spastic paralysis. Abnormal associated movements were present in the right arm and leg, but were not observed upon the left side of the body. Of the cranial nerves, the hypo- glossal showed a distinct lower motor neurone type of paralysis upon the left side, the right side being normal. The tongue presented the appearance upon the left side of many corrugations along its border, and when protrud- ed, the tip turned to the left. The somatic sensory, splniichnic mutor and sj>Iiiiichnic sensor]/ comprmenls were allnoiTual. The patient ran a constanlly liigh bloo(J piTssni'e, rangijjg from 2(10 in •220 mm. of lig. fNTERPR]5TATI0N AND AnATO.M [CAL ANALYSIS. TllO lesi(.>U waS due to ,•1 vascular accident, probably a hemorrhage. This supposition was borne nut liy the sustained high blood pressure and tlie leiminal apopleptic seiz- ure. The e\'idencc of the focus of the lesion indicates some site where tlic jiyramidal tract and hypoglossal nerve may be simultaneously involved. The most likely position for such an involvement is the point where the emergent root fibers from the hj-poglossal nerve come into relation with the pyramidal tract in the medulla oblongata. The lesion, therefore, is situated on the left side involving the left pyramid and the left hypoglossal nerve. The pyramidal fibers sulxsecjuently decussate, which exjjlains the paralysis of the right arm and leg, while the left side of the tongue is affected. The evidence of (.'ircumscription of the lesion is aiforded Ijy the absence of all symptoms referable to other motor functions, as well as the absence of somatic sensory, splanchnic motor and splanchnic sensorj' disturljances. Diagnosis and Pathology. The diagnosis of this condition is hemor- rhage into the medulla ol)longata at the level of the pyrauiid upnn the lefi si(ie. Nomenclature. This syndroine is known as hypoijlassol nlternatnuj hemiplegia or hoiiiplcgia allcrnans In/poglossica. Yariatkjns. In some cases the lesion niaj' extend aci'oss tlie mid- line and involve the opposite pyramid. When such is the case, all four ex- tremiti(^s will show some degree of pai'alysis. SuMiMARY. The essential clinical features in the syndr'Zi'd in the right arm and leg, and had lost all powers of discrimination in muscular and cutaneous sense in these part?. She i-emained in this condition until her death, which occiu'red five years later fi-om ])neumonia. Examination. Somatic Motor Component, llie idiodynamic control of the entire liody with the exception of the left side of the tongue was normal. Tlicii; was markoil a(i'o|:itiy and lower motor neurone paralysis of the left side of (lie loiit;ue. 4'he reHexes and muscle tone of the right arm and leg were much increaseii; I line was a IJaliinski on the right side, a patel- THE MEDULLA OBLONGATA 343 lar and ankle clonus and a crossed periosteal reflex. The tone in the right arm and leg was so niuch increased that these extremities were held in a rigidly fixed, abnormal position. The vohtional control over the right arm and leg was almost completely lost. Equilibratory and synergic control could not be estimated because of the spastic paralysis which masked all movements. Abnormal associated movements were present in the upper and lower ex- tremities on the right side. The tongue showed a flaccid paralysis and atrophy on the left side. The other cranial nerves were normal. Somatic Sensory Component. This conrponent showed a complete loss of discriminative sensibility in the right arm and leg, particularly discerned in defective muscle, joint and vibratory sense, as well as tactile discrimina- tion in the parts mentioned. Somatic sensibility was normal in all other parts of the body. The splanchnic motor and splanchnic sensory components were normal. Interpretation and Anatomical Analysis. The pathological process producing the symptoms was a vascular accident, probably thrombosis, as this lesion is not infrequent as a consequence of tjqDhoid fever. The evidence of the focus of the lesion points to a locality in which the discriminative sensory pathway, the pyramidal tract and the twelfth nerve might be simultaneously involved. The medulla oblongata is the only portion of the brain where these structures are in proximity; in fact, all three are in contiguity in the medulla, the pyramid lying ventral to the fillet and the emergent root fibers lying lateral to both, so that a lesion affecting this region would produce a hemianesthesia in discriminative sensibihty on the opposite side, and an upper motor neurone spastic paralysis on the opposite side with a lower motor neurone paralysis of the tongue upon the same side. The evidence of circumscription of the lesion is found in the absence of other motor symptoms, and the fact that the pain-temperature pathway shows no involvement and that no special sense is affected. The absence of any splanchnic motor or sensory symptoms further aids in the circum- scription of the lesion. Diagnosis and Pathology. This clinical condition is due to throm- bosis of the anterior spinal artery, which causes a degenerative process in the mesial fillet and pyramidal tract on the left side, and also in the emergent root fibers of the left twelfth cranial nerve. Nomenclature. This syndrome is known as hypoglossal alternating hemianesthetic hemiplegia. Variations. As in the previous case, the lesion may extend across the mid-hne, when lioth fillets and both pyramidal tracts would be involved. This would lead to disturbances in sensation and voluntary control on both sides of the body. Summary. The essential chnical features of this syndrome are: 1. Spastic paralysis, with increased reflexes and muscle tone and alj- normal associated movements contralateral to the lesion. 2. Loss of discriminative sensibility in the right arm and leg and right 344 FOIUI AND I'T'XCTIONS OF THE CEXTKAL NE11V(JT:S SYSTEM sido, of the body up to the (lorso-mcdian and ventro-iiicdiaii lines contra- lateral to tlH> lesion. , 3. The normrd status of atfeetive sensibilitj- (includinK pain and temperature). 4. The ipsilateral lower motor neurone paralysis of ll)e tongue aceom- panied bj- atrophj'. 5. Tile absence of all other motor or sensorj' disturbances, and the absence of splanchnic motoi- and sensor^' symptoms. The Syndrome of the Nucleus Ambiguus and Nucleus Accessorius. History. A cliild, three years old.ljegan to have diffieulty in swallowing. This was attendee! hy leii-m-gitation of fluids tlu-ouR-li the nose. I'he A'oicc I I'. Jiili, .1 :nid /.'. SyiiilriJiiic n( Uu- iwirlrnf^ aiiiliigiiu.s mill till' nucleus arrussurius: \-:inii-;ircessory syn- ilniriio riv syiulruuic nt Srliiiiidi. lilue indicates l(i\MT niiiliir nruvonc p:iral\'.sis nt tlic li'l't stevno- i'lciijii-ni,-isli)iil niuscli'. There is a. i)aralysis of the left \-ijcal cord. ''. ('niss sectini) through the ni(>dulla showing the loca- tion of the. lesion in the rinji.'-(ic<'r:<\nry syjirh-ojiw of Xi'lniiUU: involvenienl nf the nurleiis :iinliiguus ajid nucleus access. irius. became lio;ii-sc. The head \\;is held witli I he chin luriied toward the left. Th(; chdd could not turn her liead towaiaj tiie right. At the end of four months the jiatient had a terminal convulsion, preceded In' several hoin-s of increasing dypsnea, and died. There was a histor}- of tuberculosis in the family, the mother and an older sister having died of this disease. The patient ran a low temperature for several months, and toward the end of her sickness THE MEDULLA OBLONGATA 34:5 the teiiipei-atui'(_' gradually rose. The Yon Pirciuet test was positive; the Wasscrniann test upon the blood was uegative. Examination. Somatic Motor Component. The examination, made when the child first came under observation, showed that the idiodynamic control, the reflex and tonic control, volitional control, ecjuilibratory, synergic and automatic associated control of all parts of the body were normal. The somatic sensory component showed no disturbance of any type. The splanchnic motor component showed a distinct paralysis in the innervation of the larynx. The vocal cord upon the left side was paralyzed, which accounted for the difficulty in phonation. There was also a partial paralysis of the left sterno-cleido-mastoid and trapezius muscles, which ac- counted for the fact that the head was held toward the left and the patient was unable to turn it toward the right. The splanchnic sensory component showed no patliological disturl)aiices. The lal)orator\' findings showed a spinal fluid increased in tension and quantity', containing 200 lymphocytes to the cul)ic mm. The Noguchi reaction was positive; the Wassermann reaction was negative. Thefilood and urine showed no pathological changes. Interpretation and Anatomical Analysis. Upon postmortem examination, it was found that the child wais suffering from a small tuber- culoma in the reticular formation of the medulla oblongata on the left side. Evidence of the f(jcus of the lesion was furnished ):>y the simultaneous involvement of the left vocal coi-d, the left sterno-cleido-masloid and the ti'apezius muscles, which points to the nucleus ambiguus niid the accessor}- portion of thi; spinal accessory nucleus. Evidence of circumscription of the lesion shows that no other tracts or portions of the gray matter in the medulla ofilongata wta-e invrjlvcd, since there were no soriiatic sensorj- or splanchnic sensory symptoms, and no other splanchnic symptoms than those mentioned. This draws a distinct Ijoundary about the nucleus ambiguus and nucleus accessorius. DiACiNOsis AND Pathology. The lesion in this case was a tul)erculoma in the medulla olalongata. Nomenclature. This s>'ndrome is kno«-n as the rago-accessnr>i syndrome or the sundrumc of Sclnriult. Summary. The essential clinical features of the syndrome of Schmidt are : 1. Ipsilateral paraly.sis of the larynx (laryngojilegia). 2. Ip;-ilateralparalj'sisof tlie sterno-cleido-mastoid and trapezius muscles, pro.lucmg an inability to turn the head, so that tlie chin points to the side opposite the lesion (cephalogyric paralysis). 3. The absence of all other splanchnic motor paralysis. 4-. The absence of any somatic motor oi' sensory disturbance. Syndrome of the Nucleus Ambiguus, Nucleus Accessorius and Nucleus Hypoglossus. History. A man, forty years of age, who gave the history of having had an initial luetic lesion in his tliirtieth year, 346 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM gradually liecame aware of difficulty in swallowing and an increasing huskiness in his voice. His intonation became nasal. He also noticed that it was difficult for him to turn his head to the right. He gave a history of a positive Wassermann reaction in the blood three years before he came under of^servation. Following this report he had received some irregular antiluetic treatment for six months. After a course of intensive antiluetic therapy, his symptoms entirely disappeared. Fig. 2117. — A,JJ and C Syndnmie of tlie nucleus amtiiguus, nucleus accessorius and nucleus liypuglo.ssus; synth'onu' of vago-accessory hypoglossal paralysis: syndrome of Jackson. Blue indicates a lower motor neurone paralysis of the left sterno-cleido- mastoid and trapezius nuiscles. There is also a paralysis of the left vocal cord, the left half fif the tongue anil the left half of the soft palate. The lesion in this syndrome occupies the same location as in the syndrome of Tapia.but e.xtendscaudally to in- volve the nucleus accessorius. D. Cross section of medulla showing iin'olvement of nucleus hypoglossus and nucleus a.mliiguus. Examination. When he first came under observation, complaining of disturbances in his nervous system, he presented the following symptoms: The Soiiintiv Motor < 'onipoiwiit. With the exception of the left side of his tongue, which showed a paralysis with marked atrophy, his idiodynamic, reflex and tonic, volitional, equiUbratory, synergic and associated auto- matic controls were normal. The paralj^sis in his tongue was confined to the left side, which caused the tip of the tongue to point to the left when protruded. THE MEDULLA OBLONGATA 347 The somatic sensory component was normal in all qualities of sensibility. The splanchnic motor component showed a paralysis of the left vocal cord with a paralysis of the left half of the soft palate. The left sterno-cleido- mastoid and trapezius muscles being paralyzed, it was impossiljle for the patient to turn his head to the right. The splanchnic sensory component showed nothing abnormal. The Laboratory Findings. The Wassermann test of the blood and spinal fluid were both four plus positive. The spinal fluid showed twenty cells and a positive Noguchi reaction. After intensive treatment by the Swift-Ellis method, the positive reaction of the blood and spinal fluid disappeared. Interpretation and Anatomical Analysis. In this case the lesion was due to neurosyphihs of the meningo-vascular type. Evidence of the focus of the lesion is given by the simultaneous involve- ment of three of the cranial nerve nuclei which occupy a position in the medulla oblongata and are in close proximity to each other, namely, the nuclei of the tenth, eleventh and twelfth cranial nerves. Evidence of circumscription of the lesion is given by the absence of involvement in other portions of the splanchnic motor or sensoiy compo- nents and absence of all other somatic motor or sensory disorders. Diagnosis and Pathology. The diagnosis is neurosyphihs, aft'ecting the medulla oblongata, and the pathologj' is that of vascular neurosyphihs. Nomenclature. This is known as the syndrome of vago-accessory- hypoglossal paralysis. It is also called the syndrome of Jackson. Summary. The essential clinical features in the syndrome of Jackson are : 1. Ipsilateral paral.ysis of the soft palate (palatoplegia). 2. Ipsilateral paralysis of the larynx (laryngoplegia). 3. Ipsilateral paralysis of the sterno-cleido-mastoid and trapezius muscles (cephalogyric paralj-sis). 4. Ipsilateral paralysis of the tongue accompanied by atrophj^ 5. The absence of all other splanchnic motor and sensory cUsturbances. 6. The absence of all other somatic motor and sensory disturbances. Syndrome of the Nucleus Ambiguus and Spinal Fillet (Spino-Thalamic Tract). History. A woman, sixty-six years of age, was suddenly seized with vertigo and became unconscious. She regained consciousness in half an hour and found that she had much difficulty in swallowing and talking. She could scarcely make her voice audible. She gave a previous history of prolonged high blood pressure, ranging from 200 to 230, and at the time when she came under chnical observation her blood pressure was 265. She was kept in bed for two weeks, the possibility of an extensive cerebral hem- orrhage being apprehended. At the end of this time she was allowed gradu- ally to resume some of her usual activities. She never entirely recovered, and until the time of her death, two years later, had considerable difficulty in swallowing and talking. 348 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Examination. When examined at tlie onset of her symptoms she showed the following; The soiiiaiic motor coiiipoitf'id was normal in all respects. There was no disturbance in the idiodynamic, reflex or tonic, volitional, eriuilibratory, synergic or associated automatic control of the muscles of the body. The twelfth cranial nerve was normal. The somatic KoiKonj component showed a marked disturbance. There was a coin|)l('t(' loss of tlie pain-temijcrature sensiliilitv on the left side of Fig. 2(iS. — ,1, /J, ami ('. Symlroino nf {\\r luir-lcu^ ninUinuiis ami siiiiijil tillct (spino- thalainic Irai-t ) ; syiiilmun' n[ A\ l'lll^. Jtrd nnlicalt's a lof^s of )iain and teniperatiiro sensibility, 'riicvc is a Inwor nmlor in'inoiu' ]iaial>>:is of tlii' riiilit A'oi^alconl and right half of tin' .^oft indnto 1). Cross scrtioH (liroiigli tlio iiirdidl.a sliouiiifi Ihi' location of thf lesion in the mnd- noii.r nf Avdlis: iiivoha.nient of tlie nueleus loiiliiuniis and spino-tluilamic tract (spmal (illct;. the liody, although Ixitli sides of the face showed no sensory disturbance at any time; the; left side of the head and neck dorsal to the interauricular line sli(nved a loss <;f pain and lemi)era(ure scnsifiility. In the areas in which the afl'ective tyjies <.)f sensation were defectn-e, there was no disturbance in -^-ibi-atoiy sense, (hscriminative, tactile, muscle or joint sense. The hurt clement in sensation was completely lost or decidedly diminished on the left side of the bodj' in the areas mentioned. This was true for pinching, pressure and sharp percussion, as well as iiin-point. Sensibihty upon the right side of the bodj' was noriual in all qualities. THE MEDULLA OBLONGATA 349 The splmichiu'c motor coinponenl showed a paraly^^is of the vocal cord on the right side, also a paralj-sis of the right half of the soft palate. The splanchnic sensunj coiiipoitciit was normal. There was no change in the mental status. Laboratory findings were negative. iNTEiiPHETATiON AND AxATOMiCAL AxALYSis. The lesion, in the light of the high blood pressure, \\-as undoubtedly due to a hemorrhage in one of the radicular arteries supplying the medulla oblongata. Evidence of the focus of the lesion is given by the simultaneous involve- ment of the nucleus aml)iguus which suppHes the larynx and palate, and the spmo-tlialamic tract (spinal fillet). In the lateral white column of themed- ulla, the.se two elements lie close together, so that a smah lesion might involve both. Evidence of circumscription of the lesion is afforded by the absence of involvement of all the other cranial nerves, and by the fact that none ot the pathways, either for somatic motor or somatic sensory conduction, was affected. Diagnosis and Patiiologt. The diagnosis of this condition is hem- orrhage m the meduUa oblongata with a consequent impairment of con- duction in the spino-thalamic tract, and also impairment of the nucleus anibiguus which supplies the larynx and palate. Nomenclature. This is known as the syndrome of the spinal fdlet and nucleus ainhiguus. It is also called the syndrome of Avellis. Variations. In some cases the lesion may extend dorsallyto involve the pupillary center of the medulla, which consists of a group of cells situated dorsal to the nucleus ambiguus. When such is the case the syndrome of Avelhs is complicated by the syndrome of Horner. This .syndrome con- sists of ipsilateral enophthalmia (sinking in of the eye-ball), myosis, (nar- rowing of the pupils), and sympathetic ptosis, i.e., slight drooj^ing of the upper lid. Summary. The essential clinical features of the syndrome of Avelhs are : 1. Ipsilateral paralysis of the vocal cord and soft palate (larvngoplegia and palatoplegia). 2. Contralateral loss of pain and temperature sensibility in the leg. trunk, arm, neck and skin over the scalp up to the intcrauricular line. This loss of pain and temperature sensibility is hemisomatic. 3. The rett'ntion of all other types of somatic sensation in the areas showing defects in pain and temperature sensibility. 4. The absence of any other sensory or motor cUsturljancc in the body. Syndrome of the Nucleus Ambiguus and Nucleus Hypoglossus. History. A child six years of age, after suffering for thi'ee weeks from a prolonged slee]i as the result of epidemic encephalitis (the so-called sleeping sickness), ])resented upon examination paral}-sis and atroijliy of the left side of the tongue with paralysis of the left vocal cord and left half of the soft iDalate. At the end of several months these comlitions graduallj' im- 350 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM proved and the child finally made a complete recovery. The laboratorj- find- ings upon the blood, urine and spinal fluid were negative. Examination. Upon examination after recovering from the prolonged period of somnolence, the following sj-mptoms were observed: The somatic motor componcmt showed that all the muscular structures uf the body, with the exception of the left side of the tongue, were normal in their idiodynamic, tonic, reflex, volitional, equilibratory, synergic and automatic associated controls. The tongue showed a distinct paralyses of the left side when protruded and presented a marked atrophy. The somatic sensonj component was normal. The s-planchnic motor component showed a paralysis of the left vocal cord and the left half of the soft palate. The splanchnic sensory component was normal. Interpretation and Anatomical Analysis. The lesion in this case was the result of the encephalitis from which the child had originally suffered. Evidence of the focus of the lesion points to a position in the medulla in which the hypo- glossal and vagus nerves have Ijeen siniultane- oiLsly aft'ected. Evidence of circumscription of tlie lesion is afl'orded by the absence of all other sensory and motor symptoms, in either the splanchnic or motor components. Diagnosis and Pathology. The diagnosis of this condition is polioencephalitis, involving the medulla oblongata. The pathological process was an inflammatory reaction in this region of the brain. XoMENCL.iTURE. This is the syndrome of the nucleus arnbiguus and nuclens hiipoijlossus: it is also called the s!jn(lro)ne of Tapia. ^ ariations. The same combination of symptoms sometimes occurs from involvement due to injury to the perii^heral nerves. It is usually the result of gunsliot injuries affecting the hyijoglossal and vagus nerves in their cervical course. Summary. The essential chnical features of the Syndrome of Tapia are: 1. Ipsilateral jiaralysis of the vocal cord and soft palate (lar>'ngoplegia and palatoplegia). 2. Ipsilateral paralysis with atrojihy of the tongue (atrophic glossoi^legia). 3. Absence of all other motor and sensor}' sym]:)toms. Syndrome of the Circumferential and Intermediate Zones. His- tory. A man, sixty-fiv(> years old, on rising in the morning, had difficulty in talking. When he attemiited to swallow, th(^ fluid regurgitated through the nose and caused him to ('(lugh. He at once consulted a laryn- gologist, who found that the right ^'ocal coid and right half of the soft palate were paralyzed During tliis examination the ])atient experienced a feeling Fic. 259.— Syndrome of tlie nucleus ambiguu.s ami tlie nucleus liypoglossu.s (synd- rome of Tapia). A — Lower motor neurone paralyais of the left vocal cord. B — Lower niotur neurone paralysis of the soft palate and left half of the tongue. THE MEDULLA OBLONGATA 351 of extreme vertigo and when he attempted to "walk, he noticed that he staggered to the right. He was taken home stilL sufiermg from dizziness After several hours both eyes were noticed to be drawn over into conjugate deviation to the right side. He remained in this critical condition for a number of weeks, during which time it was necessary to feed him Ijy tube because of his marked dysphagia. Subsequently he improved and finally made a complete recovery. .4 " -B Fig. 270. — .4, B, C and D. Syndrome of the circumferential and intermediate zones; syndrome of the posterior inferior cerebellar artery. Red indicates a hcmia.synergia, swaying and lateropulsion to the right. Blue indicates aloss of all types of sensibility. Green indicates a less of or decrease in pain and temperature sensibility. There is a lower motor neurone paraly.sis of the right half of the soft palate and the right vocal cord with a. right conjugate deviation of the eyes. B. Cross section through the medulla showing the location of the lesion in the synd- rome of the posterior inferior cereheUar artery: in^-olveinent of the spino-cerehellar, spino-thalamic and descending trigeminal tracts, together with the nucleus ambiguus and vestibular nuclei. Examination. E.xamination at the time of the onset of his symp- toms; showed the following: The somatic motor component showed that idiodynamic, reflex and tonic, vohtional, and automatic associated controls were normal in all parts of the body. He suffered, however, from a marked heniiasynergia of the right side. All movements of the upper and lower extremity on the right side were made with great uncertaintj' and showed a distinct lack of cooperation in the synergic units of the right arm and leg. Inattempting to walk, he 351! F(tiLM AND Fr.M'TKINS OF THE CENTRAL NERVOUS SYSTEM swiiyi-'d to tlu' I'inlit and even staggered in this direction, giving rise to a symptom known as laleiopulsion. Equilibratoi'v control was distincUy affected. Wlien he attempted to stand, with his eyes eitlrer open or closed, there was a tendency to fall to the right or else to move his feet so as to establish a broader l.)asis iii)on which t(j support liis l)od,y. Both eyes were drawn over to the right side in an extreme lateial position. His In'poglossal nerve was noinial. The somatic serisury component showed a loss of all types of sensibility on the right side of the face and head, uj) to the interamicular line and reaching the sagittal line in front. This loss of sensation was also observed in the cavities of the nose and mouth upon the right side. In addition to this loss of sensation upon the right side of the face, the left side of the body, including the neck and the skin over the scalp up to the interauricular line, presented a decrease in the pain-temperature sensibility. The senses of smell and vision, as well as the sense of hearing, were normal. The shghtest move- ment 'if the head increased his vertigo to an extreme degree, so that it was necessar}' fur him to lie as nearly motionless as possible. The sphuichnic )ni)tor component showed a paralysis of the right vocal coixl and tlie right half of tlie soft palate. The splunctmic sensonj component was normal. Interpretation .^nd Anatomical Analysis. The lesion was evidently due to a "'.•ascular accident, in view of its sudden occurrence and its tendency toward improvement . Evidence of the focus of the lesion indicates a region in the medulla oblongata in whicli fibers concerned in ecjuilibratory and sj-nergic control, as well as the pathway for pain and temjierature scnsibilit}', are simul- taneouslj' involved. The symptoms referaljle to the nucleus ambiguus indicate a jiosition in the lateral white column. It is possible to locate in this position all of the tracts necessary to explain the symptoms. The distur- bances of eciuilibratory and synergic control indicated bj- the hemiasjmergia, th(^ ataxia and the lateropulsion, were attributed to the dorsal and ventral spmo-cerebcllar tracts. Immediately mesial to the dorsal spino-cerebellar tract at this level is situated the descending trigeminal tract, conveying afferent impulses from the same side of the face. This would explain the ipsilateral hemianesthesia of the face. The vertigo and dextroversion (turning to the right of lioth eyes in conjugate position) are explained by irritation to the vestibular nuclei situated in close relation to the descending trigeminal tract. The loss of iiaiij-temperature sensibility on the opposite side of the liody may Ije attrifniieil to involvement of the spino-thalamic tract (spinal fillet) which conveys sensory impulses from the contralateral side of the liody. Tfie ipsilateral ))aralysis of the vocal cord and of the soft palate de- notes an invoh-eiiient ol' tlie iiiulrus ambiguus mi the same side. Evidence of the focus of the lesidii placrs the pathological process in the c-ircumfei'eii1ial and intermediate zones on the right side of the medulla ()filonga,ta. Evidence of circumscri|:iiii.m of the l(>siiiii i-< furmsheich)i,ic motor and .splanchnic sensory components were normal. Interpretation and Anatomical Analysis. From the acute par- oxysmal character of the attacks, and the intervals of long duration when the i)atient was free froiu all of his symptoms, it is evident that the nature of the lesion must have been that of an angiospasm not unlike the patho- logical conditions which produce the ''twenty-four hour hemiplegia." Evidence of the focus of the lesion is furnished by the fact that the main symptoms were the overthrow of equililnatory control, accompanied by an extreme sense of vertigo and some nystagmus. If this were to be placed centrally, the mo-d likely position would l)e in connection with the vestibu- lar nuclei in the metlulla oblongata. This focus is selected from the fact that the vestibular area of the meilulla is abundantly supplied with a leash of vascular channels which make it stand out in contrast to other adjacent portions of the medulla. The high vascularity of this region of the medulla oblongata has been noted Ijy Hoyt in recent studies on the primate brain. Evidence of circumscription of the lesion is furnished Ijy the fact that the aural exanunation exem|)ted the njiddle and internal ear from all re- sponsibility in connection with the symptoms. It should be borne in mmd, how(n'er, that both the middle and internal ear may be incriminated by symj^toms of the character i-ecorded in this case. It is the clinical rule that when there is no sign of inA'olvement of the cochlear division of the eighth neive, the evidence is against an affection disturbing either the middle or the internal ear. I'urthermore, the acute, paroxysmal nature of the disease would indii"iti> some transitory lesion, inasmuch as the intervals lietween attacks were quite free from symptoms. The evidence of circumscription of the lesion is also furnished by the absence of any motor symptoms other than those due to the overthrow of equilibratory control, and also to the lack of sensory symptoms; these facts draw a line aliout the focus of the lesion limiting it to the region of the vestibular nuclei. Dl\c;nosis and Pathology. The diagnosis is an involvement of the medulla in the region of the vestiljular nuclei due to an angiospasm. Nomenclature. Idiis is the si/ndromc of tlie vestibular nuclei, and is sometimes referriM.I to as llie xfimlrnme of Meniere. It is to be notcMl that this syndrome is usually the result of involvement of the internal ear. Meniere's disease is in fact, an acute hemorrhagic con- dition involving the vi'stibular and cochlear sti-uetures of the internal ear. Variatioxs. In Meniere's disease the symptoms are similar to those of the case alicad>' recorded, with the exception, however, that the sense of hearing is implicated. Summary. The essential clinical features of Meniere's syndrome due to the involvement of the vestil ailar nu(dei are : 1. Parox3'smal attacks of vertigo with intervals either completely free from all symptoms, or during which the symptoms are negligilde. THE MEDULLA OBLONGATA OOO 2. The loss of equilibratory control. 3. The nornial state of the sense of hearing. 4. The absence of any other somatic motor or sensory disturhanee or of any splanchnic motor or sensory disorders. Syndromes Due to Multiple Lesions in the Medulla Oblongata. Several other syndromes of the medulla have been described. They occur with sufficient frequency to make them of anatomical ijiterest. These disorders are due to diffuse, multiple lesions affecting different parts of the gray and white nintter. Two of them in particular maj- lie mentioned; Fi(i. 271. — A and B. Syndrome due to niulti])l(' IcRioii.? in tlio niodulla oblongatii,: syndrome of Raliinski- Nagootti.-. Reil indicates an upper motor neurone loarah'si.s antl also a hemianesthesia involving discriminative sensibility. Blue indieatcs hemi- asvnergia, hemiataxia and lateropulsion to the right. There is also niyosis, cnophlhalmos and ptosis on the right side. C. Cross section through the medulla showing (he location of the lesions in the .•iijiiijniini' of Bnliinsla-Nagcnttc: involvement of the pyramid, mesial fillet, spino- cerebellar tracts and oculo-pupillary nucleus. A The Syndrome of Babinski-Nageotte. This syndrome results from the multtple lesions which affect the pyramid and fillet, the inferior cere- bellar peduncle and the reticular formation. Its symptoms are: 1. Contralateral hemiplegia. -> Contralateral liemianesthesia involving diK-riminative sensibihty in the arm leg and trunk, neck and scalp up to the mterauricular line on the side opposite the lesion, with retention of pam and temperature sensibility. The face is usually unaffected. 356 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM 3. Ipsilateral lateropulsioii, lieuiiasyiiergia. and heaiiataxia, due to the fact that the inferior cerebellar peduncle bearing afferent impulses from the muscles to the cerebellum has been involved. 4. ]\Iyosis, enophthalmia and ptosis (Horiier's Syndrome), due to the involvement of the oculopupillary center in the medulla olilongata. Fig. 272. — A, B, C and D. Syndrome of multiple lesions in the medulla oblongata: syndrome of Cestan-Chenais. Red indicates an upper motor neurone paralysis and a hemianesthesia affecting all types of sensibilitJ^^ Blue indicates a hemiasynergia, hemiata.xia and lateropuLsion to the rip;ht. There is a lower motor neurone paralysis of the right half of the .soft palate and left vocal cord. There is also myosis, enoph- thalmos and ptosis on the right side, E. Cross section through the medulla showing the location of the multiple lesions in the syndrome of Veslan-Chenuia: IiivohTirient of the pyr.-imiil, mesial fillet, Lspino- thalamic and spino-cerebellar tracts with the nucleus ambiguus and nucleus oculo-pupillaris. All of these symptoms could not be explained on tlie basis of a single lesion, and pathologically it has been sliown that the involvement is usually due to scattered foci in the tlistriliution of the.vertebral artery. B. The Syndrome of Cestan-Chenais. Tl)is syndrome is due to scat- tered lesions involving the p3framid, the fillet, the inferior cerebellar peduncle, the nucleus ambiguus, the oculo-pupillary center and sometimes the spino- thalamic tract. The symptoms in consequence of this involvement are: 1. Contralateral hemiplegia. THE MEDULLA OBLONGATA 357 2. Contralateral hemianesthesia, involving discriminative sensibility of the opposite leg, trunk, arm, neck and scalp, up to the interauricular hne. 3. Contralateral loss of pain and temperature sensibilitj' of the leg, trunk, arm, neck and scalp, up to the interauricular line. The sensibility in the face remains normal in this syndrome. 4. Ipsilateral hemiasynergia with lateropulsion. 5. Myosis, enophthalmia and ptosis (Horner's syndrome). 6. Ipsilateral paralysis of the soft palate (palatoplegia). 7. Ipsilateral paralysis of the larynx. The sj^mptoms are due to the scattered areas of degeneration in conse- Cjuence of thrombosis of the vertebral artery, or arise as part of a syndrome due to multiple sclerosis. CHAPTER XX THE PONS A^\ROLII SIGNIFICANCE, ANATOMY AND EMBRYOLfjOY OF THE PONS The Pons, a Structure of the Mammalian Brain. In the human brain, the portion of tlie neuraxis iinincdiately cephalad of the medulla oblongata IS the pons \^aroUi. It occupies a position in the mesial portion of the poste- rior cranial fossa. As an anatomical division of the l>rain, it takes its impor- tance from tile fact thai it a]ipeai's in manunals only and reaches its highest development in man and the anthropoid apes. It is not found in fishes, amphibia, reptiles or l)irds. The term pons, therefore, has a limited applica- tion in the description of Ihe bi'ain of vertel)rates. What accounts for its jnominence in anatomy? The answer to this question sheds much light upon many advances in the development of the brain and also reveals the pons ^"arolil in a dynamic lok' during the ])roeess of evolution. In the lower ^-ei'tetjrates, the tegmentum of the niyelencephalon is continuous with that of the metencephalon without appreciable line of ding in size that between the motor cortex of the cerebrum and the spinal cord. There appears to be a need of this connection in the mammalian brain which does not exist in lower vertebrates, while the demands made upon it are greatest in the most highly developed mammals. The pontile fibers arise in the frontal, parietal, temporal and occipital regions of one side of the cerebral cortex and establish communications with the lateral lobe of the cerebellum of the opposite side. This connection brings the cerebellum under the influence of those regions of the cerebral cortex which are related to volitional control of the muscles, to somatic sensibility and also to auditory and visual sensibility. A clew to the nature of this pallio-cerebellar connection is given in the functions attributed to the cerebellum. This part of the brain is now regarded as the important organ of synergic control. The regulation of motion mediated through the cere- bellum thus comes under the influence of the auditory, the visual, the somatic sensory and motor activities of the cerebral cortex. Man has the greatest need of such influences; the lower mammals require much le.fs. Among mammals, although synergic regulation is necessary, there are salient differences in the control of motion. The motor activities in the lower animal are to a great extent hmited to performances which are common to its kind. A quadruped has a range of action pecuUar to its species, and the animal is able to go but httle beyond this limit, however much it may be trained. In large measure its motor activities are phylogenetically conditioned — that is, they are part of the heritage of its species. Although much of the motor activity in man is similarly conditioned, there has been created an extensive superstructure of volitional control, in consequence of which the individual is capable of expanding his motor accomplishments to a remarkable degree. By far the greater part of human motor activity for this reason is onto- genetically conditioned, that is, dependent upon what the individual makes of it. Such is the case with speech and handwriting. The training of the voice in singing, dexterity in the use of certain instruments and implements, proficiency in the skilled manipulation of the arts and sciences, are all individual acquirements. Skilled acts of the kind mentioned have greater need of synergic control than more simple motor performances, and on this account the synergic organ of the brain has acquired close communication with the visual, audi- tory, and somatic sensory and motor areas of the cerebral cortex m the special interest of adequate supervision of these motions. Skilled movements vary in direct ratio with intelligence. The higher the intelligence, the richer 3G0 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM the pallio-ccrebellar connection which determines the synergic controL The modus operandi of this pallio-cerebellar connection is best conceived by picturing the course of a motion formula for a skilled act, such as hand- writing. This formula arises in the cerebral cortex and leaves the brain by way of the palho-spinal pathway to reach the muscles. Simultaneous with the despatch of this formula, impulses leave the frontal, visual, sensory and auditory areas of the brain destined for the cerebellum. These impulses have the purpose of bringing the synergic mechanism into play and of regulat- ing the muscles participating in the skilled act. Fig. 273. — Diagrammatic representation of tlie metencephalon (pons) in tlie vertebrate series. Ventral view. Lcpus (rabbit) above. Canis faniiliarjs iVlof^) below. The Pons an Index of Cortical Development. In this light, the pons Varohi stands as an index of the degree of development in the cerebral cortex. In the metencephalon, the decussation which serves the function of hearing takes place in the most ventral portion of the tegmentum. In the lower mammals the crossing fibers of this decussation form a recognizable mass called the trapezoid ho(hj. As the cerebral cortex becomes more exten- sively developed, the pons attains such si7.e that it overlaps and finally conceals this body. The manunal in which the corpus trapezoideum remains uncovered by pontile fibers has a low degree of development in its cerebral cortex. Complete concealment by the pons is indicative of an animal having a cerebral cortex with a considerable degree of expansion. THE PONS VAROLII 361 Significance of the Metencephalic Tegmentum. The metencephaUc tegmentum differs httle in its significance from that of the medulla ob- longata. In both ni3'elencephalon and metencephalon the tegmental portion serves in the same general capacity. The autonomy which the medulla holds over the vital processes finds an ancillary region in the tegmentum of the metencephalon. Although the functional responsibilities of the hind- brain may be less vital to the organism, nevertheless they are essential complements to the activities carried on by the gray matter of the medulla oblongata. This is especiallj^ true of the motor control exerted by the metencephalon over the jaw muscles which provide important actions in the ingestion of food, in its preliminary preparation bj^ mastication and its subsequent deglutition. In addition, the development of the facial nucleus contributes an auxiliary motor control necessary in several ways to the vital processes. The tegmentum of the metencephalon also contains an important center for the regulation of eye movements, the nucleus of the sixth cranial nerve. In summary, the pons Varolii is significant in its basal portion as an index of the degree of skilled movement of which the animal is capable. In its tegmental portion it is complementary to the medulla oblongata in the regulation of the vital processes, and participates in the important con- trol over movements of the eyes. Features in the Embryological Development of the Pons. In the early stages of development, the neural plate gives evidence of a more rapid progress of growth in the encephalon than in the myelon. The neural folds rise in this region more rapidly, and gradually approach each other in the mid-dorsal plane. Their first line of contact and fusion occurs in the fore- brain and subsequently in the region of the midbrain. The neural folds, however, do not come into close relation in, the region of the brain imme- diately caudal to the mesencephalon. Although a roof-plate is formed here, it remains an attenuated, membranous structure which subsequently stretches over the rhomboid space bounded by the lateral walls of the myelencephalon and metencephalon. It is difficult to draw a line of demarca- tion between these two subdivisions of the brain during the early stages of development. The fact that together they form the boundaries of the rhomboid space in the ventricular cavity has led to the use of the term rhombencephalon in the description of these two divisions of the encephalon. At the caudal extremity of the rhombencephalon the neural folds have approximated each other and formed a firm fusion across the midlme. Cephalad to this fine of fusion the central canal forms a large cavity which is the fourth ventricle. In the early stages it has a thick floor-plate, high lateral walls and an attenuated roof-plate. The lateral walls soon begin to separate, especially in the region marking the transition from myelen- cephalon to metencephalon,— a process which results m a stretching out of the thin roof-plate. During this change the roof-plate not only becomes more attenuated but also in its myelencephalic portion acquires a connection with the vascular membrane, the pia mater. It thus forms the tela chorioulea 362 FORM AND FUNCTIONS OF THE CENTRAL NDRVOUS SYSTEM inferior. The roof-plate covering the luctcncephalic portion of the fourth venti'iclc ' I'cach the level of the pontile flexure. Here they are relayed 1)}' cells whose axones extend transversely and contribute to the formation of the pons Varolii. At first these fibers adhere closely to the ventral surface of the axis, some of them even passing through the ventral white column in sucli a way as to interjiose themselves between the tegmentum and the desi'ending jiyraniidal fibers. This layer of crossing pontile fibers constitutes the slrotuni profuritiuin pontis. It has the effect of displacing the pyramidal tract fibers from their usual area in the tegmentum into a more ventral position. ]\Iany bundles of these pontile fibers interpose themselves between the fibers of the pyramidal tract, so that this tract now appears separated into many small fasciculi. The transverse fibers of the pons which cause this separation of the jiyraniidal tract into inchvidual fasciculi is the .'stratum complcxu III poniix. Another large group of pontile fibers which descends to this level takes up a position superficial to the pyramidal fibers and in a more compact mass constitutes the stratum superflciale pontis. Early in the development of these pontile fibers, a large number of cells migrate from the mantle layer of the neural tube. Their collected mass constitutes the pontile nuclei which are scattered among the stratum com- plexmn and to a lesser degree in the stratum profuni-lum and stratum super- flciale pontLs. The purpose of these cells is to afford a nucleus which serves to relay the pallio-pontilc tracts, the fibers of which end by synapsis about the cells of the pontile luiclei. The axones of the pontile nuclei pass trans- versely across the midline and enter the middle cerebellar peduncle which consummates the connection between the cerebral cortex and the hemi- spheres of the cerebellum. The pons \'arolii thus results from the invasion of the metencephalic region l;)y a large number of neuraxones arising in the cerebral cortex. These axones, descending to this level, receive a relay and, by the pontile decussation, make a connection with the ojiposite lateral THE PONS VABOLII 363 lobe of the cerebellum. The addition of the pontile nuclei to the pontile fibers completes the elements essential to the formation of the pons. The entire process is in tlie interest of establishing a connection between the cere- bral cortex and the opposite side of the cerebellum. From the manner in which this pontile formation is accomplished it is evident that the size of the pons varies directly with the volume of the pallio-cerebellar connection. Situation, Boundaries and Relations of the Pons Varolu. The pons Varohi rests upon the basi-occipital portion of the occipital bone and upon the dorsum sells'. Its lower boundary is the bulbo-pontile sulcus which, in the midsagittal line, is met by the ventro-median sulcus of the medulla. The junction of these two sulci is continued for a considerable distance under the stratum superficiale pontis, giving rise to a bhnd pit, the foramen 364 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM cecum posicrius. The bulbo-pontile sulcus is also known as the 'post-pontile sulcus. The upper border of the pons is determined by the pedunculo-pon- tile sulcus, which crosses the cerebral peduncles at the cephalic margin of the pons. This is known also as the pre-pontih sulcus. It is met in the sagittal line by the cephalic continuation of the ventro-median sulcus, and the point of union of these two sulci is continued under the free edge of the stratum supcrficiale pontis for some distance, forming a blind pocket, the foramen cecum anterius. Ventral to the pons is the dura mater covering tlie mesial portion of the posterior fossa of the skull, the vertebral arterj^ and the two abducens nerves. Laterally, it is in relation with the two middle cerebellar peduncles and also with the lateral lobes of the cerebellum. Dorsall_v, it is in relation with the vermis of the cerebellum. Dimensions and Coverings of the Pons Varolii. The pons Varolii is 25 mm. in its long axis and 30 to o5 mm. in its transverse axis. Its dorso- vcntral diameter varies from 9 to 11 mm. It is covered by the pia mater which adheres closely to its surface and penetrates between the numerous transverse ridges upon the ventral surface of the pons. The arachnoid, ventral to the pons, forms a special compartment, the cisterna pontis. This is continuous behind with the cisterna magna, and in front with the cisterna basalis. Arteries of the Pons Varolii. The pons receives its vascular supply from the median branches of the basilar arter}-, which send small branches to the nuclei of the fifth, sixth and seventh nerves. In its cephalic portion it receives branches from the superior cerebellar arterj' and anterior inferior cerebellar arterv- External Markings and Surface Features of the Pons Varolii. The transition from the medulla to the pons Varolii is identified by the appear- ance of the caudaimost pontile fibers which define the bulbo-pontile sulcus. Upon the ventral surface, the pons forms a quadrilateral figure bounded cephalad by the pedunculo-pontilc sulcus and caudad by the bulbo-pontile sulcus. Laterally, the l)0undaries are not clear, but the ventral surface turns dorsad to form the middle cerebellar peduncle. The ventral surface is characterized bj' a median furrow, the basilar groove, lodging the basilar arterjr, and by a serjes of shallow, incomplete sulci running at right angles to the basilar groove. The lateral surface of the pons is concealed from view by the overlapping lateral lobe of the cerebellum; when this is retracted, the lateral surface has the appearance of a truncated cone, its apex directed toward the great transverse fissure of the cerebellum. The change in the size and shape of the pons at this point is due to the fact that the pontile fibers are drawing together into a dense mass, and also because there are now no cells of the pontile nuclei present. The structure upon the lateral surface is the middle cerebellar peduncle, the final link in the connection between the cerebral cortex and the lateral lobe of the cerebellum. Near the cephahc extremity of the lateral surface are the entrant and emergent fibers which make up the roots of tlie trigeminal nerve. THE PONS VAROLII 365 The dorsal surface of the metencephalon is concealed by the cerebellar vermis. Removal of the cerebelliim discloses the floor of the fourth ventricle which consists of a cephalic triangle in relation with the metencephalon, and a caudal triangle in relation with the myelencephalon. The apex of the ce- phahc triangle is directed cephalad, and the apex of the caudal triangle is directed caudad. The two triangles meet at their bases and together form Optif Chiasm Optif Tract _- — Tubfr Cinerpum — I\lxmmilUr\ Bodies Pet roso- Ventricular iSurfarp of the Cerebellum Great H jrizontal Fissun of thp Cerebpllurp -^^ rostcrior Ceribrllar \otch Fig. 275.— Tlic optico-peduncular space, pons, certbellum, medulla viewed from the front after removal of the pia mater, {Dejerine.) The Roman numerals indicate the oranial nerves b.v number. /-—Cerebral peduncle. Pu— Pons varolii. Oi— Olivary etiiincnrc. /„,r— Cerebellum. the rhomboid space, from which this part of the brain is Imown as the rhombencephalon. The Floor of the Fourth Ventricle. Boundaries. The boundaries of the lower triangle of the fourth ventricle are the clava; and the cunei. Both of these structures in their more caudal portions form high elevations on either side of the triangle; but as these eminences approach their cephalic extremities they become reduced in prominence until they finally reach 366 FORM AND FrNCTIONS OF THE CENTRAL NERVOUS SYSTEM the level of the floor of the ventricle. The lateral recesses extend outward at this point. The boundaries of the cephalic triangle are much higher, and consist of the middle cerebellar peduncle and the superior cerebellar peduncle, which latter forms the most extensive portion of the lateral Ijoundary. The roof of the caudal triangle is formed by the tela chorioidea irtferior, or inferior medullary velum, which is attached to a thin line of gray matter extending along the border of the caudal triangle, the tenia inedullaris inferior. The tenia medullaris is continued laterally and affords a line of attachment for the tela chorioidea inferior in forming the cvagination of the lateral recesses. The roof of the cephalic angle of the ventricle is formed by the superior medullary velum, upon which rests the hngula of the cere- bellum. Certain portions of the inferior vermis of the cerebellum project into the ventricle; these are the nodule and a part of the uvula. Features in the Floor of the Fourth ^'ENTHICLE. The floor of the fourth ventricle is divided into two synimetrical halves by a median sulcus which runs from the apex of the lowei- triangle to the apex of the upper triangle. A second sulcus starts beneath the obex, lateral to the median sulcus, and proceeds cej^halad, forming a curve which follows the lines of the lateral \\'alls. It is situated about midway between the median sulcus and the lateral walls. This is the xulcus limitans which tlivides the floor of the ventricle into a mesial motor portion derived from the basal plate, anti a lateral sensory portion derived from tlie alar j^late. The most minute description of the ventiicular floor lias been gi\-en by Streeter, whose meas- urements of the several structures are here quot(>d. In the caudal triangle, immediately adjacent to the median sulcus, is a long, narrow elevation, .5.2 mm. I)y 1. mm., and 1. mm. in thickness. This is the eniinentia hypoijlossi, which indicates the rounded, frontal end of the hypoglossal nucleus. The remainder of the hypoglossal nucleus is covered by other structures, its entire length being 12.2 mm. The intra- ventricular jiortion of tlu' nucleus is 7. mm. long. Cephalad of the eniinentia hypoglossi, and upon either side of the median sulcus, is a less prominent elevation formed by the nucleus funiculi tcrctis. This measures 5.7 mm. by 1. mm. The eminence formed by this nucleus varies in dift'erent specimens, according to the arrangement of the striisacousticai, which have their medial terminations in this area. It has been suggested that there may l)e a relation l)etween the nucleus funiculi teretis and the striae acoustica'. In a position lateral t f^'^'-^m. Median Sulcus of the 4th /' Ventricle ^'- ^^^^^^^ / Locus Ceruleus mlnentia Facialis Abducent 13 ro\ ea Superior Restiform Body ^^ Fovea Inferior Tenia of 4th \ entncle ^ Calamus Scrpitrnus Tuberculum Tnj^emmum Funiculus &ra dis (Cioll) Funiculus Cuneatu^ BurJach) Fun Tuhrr ul-in VrDusticum \rpa Acoustica -Iri^onum X. Hypoglossi ostenor ^ledian Fissure Piramedianus Posterior ateral Sulcus Fig. 276. — The fourth ventricle viewed from behind. The cerebellum and the chorioiil plexus of the fourth ventricle have been completely removed; the brachia conjunctiva with the velum medullare anterius and the lamina quadrigemina have Ijeen partly cut away. {S-paltehoUz.) Lateral and dorsal to the funiculus separans is the areapostrema, whose boundaries are the tenia meduUaris and the funiculus separans. This area e.xtends forward without sharp hne of demarcation into the region lying immediately cephalad to it, the area acoustica. All that portion of the floor of the ventricle, in both the caudal antl cephalic triangles, which hes lateral to the sulcus limitans, belongs to the acoustic area. This area consists of a mesial or vestibular field and a lateral or cochlear field. The vestibular field forms an irregular shaped elevation 368 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM measuring 16.1 miu. by 4.5 mm., which extends from the fovea superior (fovea trigemini) to the nucleus funiculi gracilis. The floor of the fourtli ventricle is traversed at the line marking the union of the bases of the two triangles by a number of transverse fibers which enter at either lateral recess. These are the striw acousticcE. They usually extend transversely across the floor of the ventricle in the position mentioned, and terminate in the median sulcus into which they dip downward. They are, however, in- constant in this relation, oftentimes running obliciuely cephalad, or quite as frequently obliquely caudad. Immediately cephalad of the transverse fibers of the striae acousticae and adjacent to the niechan sulcus, is a rounded elevation 4. mm. in diameter, which is formed by the genu of the facial nerve encircling the nucleus ab- ducens. This is the eminentia abducentis. Partly overlapping tliis elevation and extending forward to the aqueduct of Sylvius is a longitudinal elevation consisting of scattered nerve fibers with scattered groups of small or medium- sized multipolar cells. Since its function is unknown, it is called the nucleus vncertus. Situated between the two nuclei, on either side of the median sul- cus, is a shallow depression measuring 5.7 mm. by 1. mm. in diameter, the fovea mcdicma. The fasciculus longitudinalis posterior here lies immediately beneath the floor of the ventricle, covered b}' a thin layer of central gray matter. In a position lateral to the nucleus incertus is an elongated depres- sion in the floor of the ventricle 3.2 mm. in its greatest width, which becomes narrower as it extends cephalad. This is the fovea trigemini or fovea superior. Cephalad of the superior fovea is the locus ceruleus, which continues for some chstance into the aqueduct of Sylvius. It owes its color to the pigment cells constituting a large i)ortion of the area, on account of which this region is referred to as the substantia ferrugint'a. CHAPTER XXI THE PONS VAROLII INTERNAL STRUCTURE AND HISTOLOGY OF THE PONS The transition from medulla oblongata to pons with the changes in the internal pontile structure are best appreciated by means of cross sections at ,five successive levels. 1. Through the caudal limit of the pontile fibers. 2. Through the caudal Umit of the trapezoid or cochlear decussation. 3. Through the level of the caudal hmit of the genu of the facial nerve. 4. Through the level of the nucleus masticatorius. 5. Through the level of the decussation of the trochlear nerve. The description of the internal structure of the pons includes the ar- rangement of the gray and white matter in the two major portions of this division of the brain, namely, the tegmentum, or pars dorsalis pontis, and the basis, or pars basilaris pontis. Arrangement of the Gray and White Matter at the Level of the Caudal Pontile Fibers. The Gray Matter in the Tegmentum (pars dorsalis pontis). 1. The Central Gray Matter. At this level the central gray matter a slight inclination from either side toward the median sulcus. The ven- tricular floor here has its greatest transverse extent. Beginning in the median sulcus, the central gray matter contains the nucleus funiculi teretis, a col- lection of small and medium-sized cells. Lateral to this nucleus is the cephalic limit of the nucleus prepositis hypoglossi, while occupying a large adjacent triangular area is the nucleus vestibularis triangularis of Schwalbe. At the extreme lateral boundary of the ventricular floor is another vestibular nu- cleus containing cells somewhat larger than those found in the triangular nucleus, the nucleus angularis of Bechterew. 2. The Reticular Formatio7i. The white and gray portions of the reticu- lar formation occupy the central portion of the tegmentum. At the ventro- lateral extremity of the formatio reticularis alba is the large nucleus facialis, dorso-lateral to which is the substantia gelatinosa, much reduced in size. Situated in the raphe about midway between the floor of the ventricle and the ventral surface of the pons is the nucleus centralis inferior. There are no new elements in the gray matter of the tegmentum at this level. The White Matter in the Tegmentum. 1. The Ventral White Column. As in the medulla, the ventral white colunm contains the col- 24 369 370 FORM AND FITNCTIONS OF THE CENTRAL NERVOUS SYSTEM d J3 -73 o Q 2 (3 THE PONS VAROLII 371 lected fibers of the mesial fillet and the fasciculus predorsalis. The fascic- ulus longitudinalis posterior lies immediately beneath the nucleus funiculi teretis. 2. The Lateral White Column. The central tegmental tract is still situ- ated near the center of the tegmentum, while lateral to it are the descending root of the fifth nerve, the rubro-spinal, the spino-thalamic and the ventral spino-cerebellar tracts. The circumferential zone in the strict sense no longer exists, for the reason that the transverse fibers of the pons have already taken up a circumferential position. The fasciculi which make up the inferior cerebellar peduncle constitute a massive structure situated in the dorso- lateral portion of the pons. Arrangement of the White Matter in the Basis (pars basilaris ■pontis). A large collection of transverse fibers in a compact bundle sweep from one side to the other across the ventral surface of the tegmentum. They appear to be suspended from the dorso-lateral portion of the brain- stem and to be made up of axones passing from one side to the other. These transverse fibers constitute the stratum superficiale pontis, the most super- ficial layer of fibers found in this part of the brain. Dorsally, this collection of fibers is in contact with the ventral surface of the pj^ramids. Emergent and Entrant Root Fibers. At this level the more cephalic fibers of the cochlear division of the eighth nerv e are in connection with the ventral cochlear nucleus, while the vestibular fibers of the eighth nerve are making their way toward the nucleus of Schwalbe and nucleus of Bechterew. Emergent fibers arising in the facial nucleus appear in the first part and fourth part of their course. Axones from the nucleus project dorsally and mesially, as if making their way to the floor of the fourth ventricle. As they leave the nucleus they are not collected into a dense bundle but have the appearance of a loose fasciculus extending toward the nucleus prepositus hypoglossi. Arrangement of the Gray and White Matter at the Level of the Caudal Limit of the Trapezoid Decussation. The Gray Matter in the Tegmen- tum. 1. The Central Gray Matter. At this level the central gray matter is much reduced in size and the ventricle is decreased in all diameters. Its floor is much less extensive than in the preceding section, and its lateral walls consist of some of the fibers of the middle and superior cerebellar peduncles, but are made up mainly by fibers of the superior cerebellar peduncle. The roof of the ventricle contains the nucleus tecti. The general outline of the ventricle in cross section is oval. The nodule of the inferior cerebellar vermis projects into it. The central gray matter in the floor of the ventricle is reduced in extent. Immechately adjacent to the median sulcus is the nucleus funiculi teretis, which overlies the caudal extremity of the nucleus abducentis. Lateral to this collection of cells is the nucleus vestibularis triangularis of Schwalbe, and in the most lateral position of the floor of the fourth ventricle is the nucleus angularis of Bechterew. 372 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM 2. The Reticular Formation. The reticular formation contains the large forniatio reticularis grisea and the somewhat reduced formatio reticularis alba. In the gray portion of the reticular formation, a new nucleus has made its appearance, the nucleus reticularis tegmentis, ventro-lateral to which is another new element, the nucleus oliraris superior. The substantia gelatinosa is reduced in size and lies dorso-lateral to the nucleus facialis. The Gray Matter in the Basis Pontis. The appearance of the pons at this level differs considerably from that noted in the preceding section. Among the transverse fibers is interposed a large collection of gray matter constituting the pontile nuclei (nucleus pontisj. This is an extensive nucleus which serves as a rela)' for the fibers reaching the pons from the cerebral cortex and which, after synapsis, form part of the crossed pallio-cerebellar pathtvay. The White Matter in the Tegmentum. The Ventral White Column. The previous dorso-ventral relation existing in the tracts of the ventral white column has undergone considerable change. The pyramid, the most ventral of these tracts, has severed its connection with the tegmentum and has taken up a position in the pons. The mesial fillet has been col- lected into a triangular bundle and shows a tendenc3^ in some of its most ventral fibers to move into a lateral position; it has the appearance of an inverted letter V. which, due to pressure upon its apex, is gradually flatten- ing out so that its two arms ])ass from an oblique to a horizontal position. The dorsal limit of the mesial fillet is separated by a considerable dis- tance from the next dorsal element, the fasciculus predorsalis, which, together with the fasciculus longitudinalis posterior, occupies its usual area near the floor of the fourth ventricle. The nucleus funiculus teretis covers the dorsal surface of the fasciculus longitudinalis posterior. 2. The L(U?.ral White Column. At this level the central tegmental tract is still present, mesial to the facial nucleus and lateral to the nucleus reticularis tegmenti. Dorso-lateral to the superior olive are the spino- thalamic, the rubro-spinal and the ventral spino-cerebcllar tracts. The descending root of the fifth nerve occupies a position lateral to the much reduced substantia gelatinosa. An important new element in the white matter at this level is the beginning of the trapezoid or crjchlear decussatio7i. Its fibers, arise in the superior olive, make their waj- ventral to and through the mesial fillet to the raphe, where they undergo a complete decussation. This constitutes the l)cginning of the trapezoid decussation. The White Matter in the Basis Pontis. The white matter in the basal portion of the pons consists of the transverse fibers forming the stratum superficiale pontis. Emergent and Entrant Root Fibers. Some of the emergent fibers of the sixth nerve are about to make their way from the tegmentum into the basis. In this course they traverse the mesial fillet and pass between the fasciculi of the pyramidal tract. This constitutes the second portion in the emergent course of the sixth nerve. It marks a locality in the brain-stem THE PONS VAROLII 373 where injury or disease may simultaneously affect the abducens nerve, the mesial fillet and the pyramidal tract, as well as fibers in the secondary ^ J Of > a ' c a o o > si o ■73 t3 I- d 00 6 cochlear pathway. Two portions of the seventh nerve appear at this level, the first part consisting of scattered fasciculi emerging from the nucleus and 374 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM proceeding dorso-iiiesially toward the floor of the ventricle, and the fourth part, representing the last stage of its emergent course. The collected mass of the vestibular division of the eighth nerve is also seen coming into relation with the vestiliular nuclei and entering into the formation of the descending vestibular root. Arrangement of the Gray and White Matter at the Level of the Genu of the Facial Nerve. The Gray JNIatter in the Tegmentum. The central gray matter in the floor of the ventricle is further reduced in size, while its lateral boundary is now the superior cerebellar peduncle. The most prominent structure at this level is the nucleus funiculi teretis which projects into the ventricle as a large eminence caused by the presence of the nucleus abtlucentis. Lateral to this prominence are the nucleus vesti- bularis triangularis of Schwalbe and the nucleus angularis of Bechterew. The reticulai- formation contains a fairly large gray portion and a somewhat smaller white portion. The nucleus reticularis tegmenti has increased in size and is situated adjacent to the raphe upon either side. The superior olive is still present and is somewhat enlarged. Mesial to it is the nucleus trapezoideiis, a jiart of the relay system of the cochlear division of the eighth nerve. The substantia gelatinosa is reduced in size and lies mesial to the entrant root fibers of the fifth nerve. The (iR.\Y Matter in the Basis Pontis. The gray matter of this portion of the pons is much more extensive, consisting of the large pontile nucleus which is interspersed among the transverse pontile fibers. The White AIatter in the Tegmentum. The white matter has undergone marked alteration. It has lost one of its chief elements, the pyramid, which oecuiues a more ventral position in the pons. The mesial fillet forms the most ventral structure in the tegmentum and is also changed in shape and arrangement; its long axis extends trans- versely from one side of the section to the other. Dorsal to the fillet are the nucleus reticularis tegmenti, the fasciculus predorsalis and the fasciculus longitudinalis posterior. The latti-r bundle is in close relation with the second portion of the emergent root fibers of the seventh nerve, which, in combina- tion with the nucleus abducentis, produce a bulging in the floor of the fourth ventricle, the ein.inentia ahducentis. The lateral white column contains the central tegmental, rubro-spinal, spino-thalamic and ventral spino-cerebellar tracts, as well as the descending root of the fifth nerve. A collection of horizontal fibers from the superior olive to the nucleus abducens constitutes the peduncle of the inferior olive. which serves as a reflex connection, causing the eyes to turn in the ilirection of sounds received by the ear. In the lateral white column adjacent to the extremit.y of the mesial fillet is a collection of fibers making an ascending course; these constitute the lateral fi.llet and represent the fibers which cross in the trapezoid decussation to form the secondary connection in the cochlear imthway. Another group of fibers situated in the dorso-mesial portion of the lateral white column are the striis acousticse profundse which take origin in THE PONS VAROLII 375 the dorsal cochlear nucleus and make their way to the trapezoid decussation. The White ^Matter in the Basis Pontis. The pons consists of two groups of transverse fibers, the stratum superficiale pontis profundum pontis. and the stratum 37G FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Emergent and Entrant Root Fibers. The first portion of the sixth nerve makes its way from its nucleus through the tegmentum and the mesial fillet. The second and fourth parts of the seventh nerve are present at this level, the second part lying dorsal to the fasciculus longi- tudinalis posterior. The tliird portion or genu of the seventh nerve passes around the nucleus of the sixth nerve, making its way outward to the fourth portion. Arrangement of the Gray and White Matter at the Level of the Nucleus Masticatorius. The Gray Matter in the Tegmentum. 1. The Cen- tral Gray Matter. The central gray matter is much reduced in size and the floor of the ventricle is decreased in its transverse diameter. The lateral boundary of the ventricle is formed by the superior cerebellar peduncle. The nuclear elements in the floor of the ventricle have diminished in size and number. Adjacent to the median sulcus, which has become some- what broader to form the fovea mcdiana, is a collection of small and medium sized cells, the nucleus incertus. Ventral to the nucleus of Schwalbe is a collection of large motor cells which give rise to the motor division of the trigeminus nerve, the nucleus masticatorius. 2. The reticular formation contains a large central griseal portion and a small white portion. Adjacent to the raph^ is the large nucleus reticularis tegmenti and still further lateral is the cephalic extremity of the superior olive and the much reduced substantia gelatinosa. The Gray Matter in the Basis Pontis. The gray matter at this level of the pons is much increased in the size and richness of the pontile nuclei. The White Matter in the Tegmentum. 1. The ventral white column consists of the mesial fillet, dorsal to which is the nucleus reticularis teg- menti, the fasciculus predorsalis and the fasciculus longitudinalis posterior. The latter bundle is situated ventral to the second part of the seventh nerve, which is turning into the third part of its course to form the genu facialis. This bundle of fibers is situated Ijcneath the nucleus incertus. The facial nerve arises from a nucleus caudal to the nucleus abducens, and sends its first part as a spray of fibers toward the floor of the fourth ventricle, where it passes into the second part of its course as a collectetl bundle of fibers. This bundle makes its way mesial to the abducens nucleus beneath the floor of the ventricle to the cephalic extremity of the nucleus of the sixth nerve. Here it turns transversely outward beneath the floor of the ventricle to form the third part of its course, the genu of the seventh nerve. The bundle of facial fibers finally turns ventrally and caudally, to emerge from the bulbo-pontile sulcus in close relation to the two divisions of the eighth nerve. 2. The Lateral White Column. This column contains the central teg- mental, the rubro-spinal, the spino-thalamic, the ventral spino-cerebellar tracts, and the beginning of the descending root of the fifth nerve. The White Matter in the Basis Pontis. In addition to the THE PONS VAROLII 377 stratum superficiale pontis and the stratum profundum pontis, an- other group of transverse fibers has interposed itself in the pons. This is the stratum complexum pontis. These crossing fibers pass in and out between the several fasciculi of the pyramidal system, subdividing it into a number of smaller, separate groups of fibers. 378 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Neur tlie junction of the stratum pi'ofundum and the tegmentum, a number of pyramidal fillers pass dorsally as if about to enter the tegmentum of the pons. These fibers constitute the pontile contingent of the aberrant pyramidal sydcm and serve to carrj^ vohtional impulses to the nucleus of the seventh, ninth, tenth, eleventh and twelfth cranial nerves. After leaving the stratum profunduju, the fibers of the aberrant pyramidal system be- come incorporated with those of the mesial fillet. Emergent and Entrant Root Fibers. The chief nerve roots at this level are the emergent fibers of the facial nerve. Arrangement of the Gray and White Matter at the Level of the Decus- sation of the Trochlear Nerve. The Gray Matter in the Tegmentum. 1. The Central Gray Matter. The central gray matter surrounds the ven- tricle, which has been reduced to a small triangular cavity. In the floor of the ventricle the central gray matter is arranged as two lateral masses ex- tending obhquely up to the roof-plate. The roof consists of the superior medullary ■s'elum through which pass the decussating fibers of the trochlear nerve, the only motor nerve which undergoes complete decussation before its emergence from the Ijrain-stem. Beneath the median sulcus, the central gray matter contains the nucleus dorsaUs raphe, lateral to which is a collec- tion of large motor cells having a bluish or brownish color, the locus ceru- leus. ^"entral to these cells are some large gryochrome elements intermingled in part with those of tlie locus ceruleus, which constitute the mesencephalic nucleus of the trigeminal nerve. Dorsal to the locus ceruleus is the descend- ing portion of the trochlear nerve. In their emergent course the fibers of the fourth nerve descend to this level, make a sharp dorsal curve, reach the superior medullary velum and pass inward across the median line, where they meet the corresponding fibers from the opposite side. After this decus- sation the trochlear nerve emerges from the lateral margins of the superior medullaiy velum. 2. The Reticular Fonnation. The reticular formation has been sub- divided into a ventral and a mesial portion by the ventro-mcsial migration of the superior cerebellar peduncle, which is assuming a position prepara- tory to its decussation. The mesial portion of the reticular formation contains the formatio reticularis grisea. In the center of the tegmentum on either side of the raph6 is the nucleus centralis superior. The ChtAY Matter in the Basis Pontls. There is an increase in the size of the pontile nucleus, but no new elements have made their appearance at this level. The White Matter in the Tegmentum. 1. The Ventral White Column. It is difficult to recognize the limits of a ventral white cohunn, since many changes have occurred in the arrangement of the ascending and descending tracts. The ventral column is occupied bj- the mesial fillet which now lies directly transversely across the brain-stem, although it shows some tendency for its lateral portion to turn into a more dorsal position. In the circumferential zone there is a thin layer of gray matter, immediately mesial THE PONS VAROLII 379 to which are the following tracts: The ventral spino-cerebellar tract, which at this point is turning backward to cross the lateral surface of the superior cerebellar peduncle on its way to the cerebellum ; the lateral fillet or second- ary cochlear pathway; ventral to the lateral fillet is a narrow strip of white 3S0 FORM AND FUNCTIOiNS OF THE CENTRAL NERVOUS SYSTEM matter which contains the .spin(j-thalauiic tract ; iniiiiediatcly dorsal to the lateral pxtrcniit,v of the lateral fillet is the rubrospinal tract. All of these tracts are arranged in the form of the letter L, the vertical limb being rep- resented by the lateral fillet and the spino-thalamic tract, while the hori- zontal limb contains the rubrospinal tract and the mesial fillet. Interspersed among the fibers of the mesial fillet, and occupying a position at its mesial extremity, are fibers of a different category from those consti- tuting the bulk of the mesial fillet itself. These are descending fibers which have become associated secondarily with the fillet. They descend originally in relation with the pyramidal tract and represent the pj^ramidal fibers designed to Ijring volitional control to certain of the cranial nerve nuclei. Mesial to the circumferential zone is the ventral portion of the reticular formation, the mesial boundary of which is the superior cerebellar peduncle. INIany fibers of the superior cerebellar peduncle pass inward toward the median line preparatory to their decussation in the midbrain. The circum- griseal portion borders upon the formatio reticularis grisea, near the center of which courses the central tegmental tract and, in a more mesial position, the fasciculus predorsalis. Beneath the central gray matter, on either side of the median line, are the collected fibers which form the fasciculus longi- tudinalis posterior. Lying inuncdiately beneath the ependyma lining the ventricle are the fibers of the fasciculus longitudinalis dorsalis of Schtitz. The White Matter in the Basis Pontis. The arrangement of the transverse fibers of the pons is similar to that in the preceding section, although the stratum complexum pontis has become more complicated and has caused a further separation in the individual fascicuh of the pyramidal tracts. The stratum profundum has about disappeared, and the stratum supcrficiale is much reduced in its dimensions. The connection of the pons fibers with the middle cerebellar peduncle is not evident at this point, as the section carries the plane through the brain-stem at a point cephalad to the level of the peduncle. E.MERCiKNT Root Fibers. The only nerve roots connected with this level of the brain-stem are the emergent fibers of the nervus trochlcaris, which, after complete decussation in the superior medullary A'clum, emerge in a manner dissimilar to that of any other of the cranial nerves. The reason for this decussation in a motor nerve controlling one of the eye muscles, as well as for its aljerrant course and emergence, is not clear. This region of the brain-steiri connected with the emergence of the trochlear nerve has been referi'ed to as the islhmns iii-etenccphali. Summary of the Relations of the Gray and White Matter of the Pons Varolii. Cross sections through the pons show manj* changes as compared with the spinal cord and the medulla. These changes are occasioned by the appearance of certain elements not observed in other parts of the brain, as well as l>y tlie disappearance of several familiar landmarks. The principal change is the addition of the tran.sverse pontile fibers constituting the pars basilaris pontis, together with the appearance of the extensive pontile THE PONS VAROLII 381 nuclei. The distinction between the l)asis and the tegmentum of the pons is clearly indicated, but it is no longer possible to recognize dorsal, lateral or ventral gray columns. The central gra}' matter, however, retains a gen- eral resemblance to the conditions observed in the medulla oblongata. Features of the AIetencephalic Gray and White Matter. Cer- tain features of the gray and white matter are especialh^ characteristic of the metencephalon. The following are the principal characters in the gray matter: 1. The nucleus facialis. 2. The nucleus abducens. 3. The nucleus masticatorius (motor nucleus of the fifth nerve). 4. The vestibular nuclei of Bechterew and Schwalbe (nucleus angularis vestibularis, nucleus triangularis vestibularis). 5. The nucleus of the superior olive (superior olive). 6. The nucleus trapezoideus. 7. The pontile nuclei. 8. The mesencephalic nucleus of the trigeminal nerve. 9. The nucleus of the lateral fillet. The following features are characteristic of the white matter in the metencephalon : 1. The three strata of pontile fibers, including the stratum superfi- ciale, the stratum profundum and the stratum complexum. 2. The middle cerebellar peduncle. 3. The rearrangement of the mesial fillet from a dorso-ventral to a trans- verse position. 4. The appearance of the aberrant pyramidal fibers in connection with the mesial fillet. 5. The superior cerebellar peduncle. 6. The appearance of the lateral fillet. 7. The dorsal shift of the ventral spino-cerebellar tract. 8. The maintenance of the rubrospinal and spino-thalamic tracts in positions corresponding closely to those occupied by these fascicuh in the spinal cord. This part of the brain presents three principal decussations: 1. The trapezoid decussation. The decussation of the trapezoid body or crossing in the secondary pathway of hearing. 2. The complete decussation of the trochlear (fourth cranial nerve) in the superior medullary velum. 3. The complete decussation of the pallio-cerebellar pathway. Nerves Connected with the Pons. Five of the cranial nerves are connected with the pons "S'arohi. 1. The trochlear neive makes part of its descending intra-axial course and undergoes decussation in this region of the brain. 2. The trigeminal nerve has its motor nucleus and the cephahe extremity of its sensory receiving nucleus in the metencephalon. 3. The abducens nerve has its nucleus in the metencephalon; its emer- 382 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM gent fibers pass through both the tegmental and basal portions of the pons before emerging. 4. The facial nerve has the major portion of its motor nucleus and the cephalic extremity of its sensory receiving nucleus (the nucleus fasciculus solitarius) in the metencephalon. All four portions of the emergent fibers of the seventh nerve make their way through this part of the brain-stem. This includes: the first part, consisting of diffuse axones; the second part, mesial to the nucleus abducens and forming part of the eminentia abducentis in the floor of the fourth ventricle; the third part, the genu of the nerve; and the fourth part, by means of which the nerve fibers descend from the genu and finally emerge from the bulbo-pontile sulcus in relation with the two divisions of the eiglith nerve. .5. The vestibular division of the eighth nerve has important receiving nuclei in the metencephalon. The cochlear division of this nerve also receives a relay in the tegmental portion of the pons. CHAPTER XXII THE PONS VAROLII FUNCTIONS AND PRINCIPAL SYNDROMES OF THE PONS Functions of the Gray Matter. The inetencephalon acts in a comple- mentary capacity to manj^ of the functions of the medulla. Primitively the tegmentum of the myelencephalon and metencephalon constituted a com- mon autonomous area essential to the regulation of the vital processes. This autonomous area still exists in man, although pontile structures have been added to it. Splanchnic Motor Functions of the Pons. 1. Through the motor nucleus of the trigeminal nerve, the nucleus masticatorius, the pons in- nervates several glands as well as the following muscles of mastication through the portio-minor of the trigeminal nerve : the temporal muscle, the masseter muscle, the external and internal pterj'goid muscles, the mylohyoid muscle and the anterior belly of the digastric muscle. It supplies glandular effector impulses to the sul)maxillary and subhngual glands. In all probability, it innervates, in part at least, the lachrymal gland and also the sudoriferous and sebaceous glands of the face and fore part of the head. 2. Through the motor nucleus of tlie facial nerve, the pons innervates the following musculature: all of the muscles of expression, the intrinsic and extrinsic muscles of the external ear, the stylohyoid muscle, the posterior belly of the digastric muscle, the platysma myoides muscle, the stapedius muscle and perhaps some portion of the levator palati and azygos uvulae muscles. Through the seventh nerve, the pons contributes impulses to the sub- maxillary, subhngual and lachrymal glands. Clinically, the most significant feature of the pontile innervation of the facial musculature is the fact that the muscles of expression are grouped in three divisions, namely, those in the upper, middle and lower face. Each division receives its nerve supply througli a special branch of the facial nerve. When the facial nucleus is affected by disease or suffers from injury on one side, all of the muscles on the corresponding .side of the face become paralyzed. This is also true if the nerve fibers constituting the facial nerve are injured or diseased. A complete paralysis of all the muscles on one side of the face is known as the peripheral type of facial palsy. This paralysis differs from that in which the connection of the facial nucleus with the cerebral cortex is defective in any part of its course from the origin in the motor area to the nucleus. Such a lesion produces a paraly.sis hniited to the 3S3 384 FORM AND FtFNCTIONS OF THE CENTRAL NERVOUS SYSTEM Latera nilet Mesial nilet Mesial nilet (Cephahc Ventricular yeveloflheMedulla Mesial nilet ■Inferior Olive 282. — The pyramidal tract as it passes throuf^b the pons on its way from the giant cells of the precentral cortex to the ventral gray column cells of the spinal cord. This tract serves for the conduc- tion of impulses of volitional control over the somatic muscula- ture. THE PONS VAROLII 385 middle and lower facial muscles of the opposite side. The upper portion of the muscles of expression, the occipito-frontalis and the corrugator super- cihi, remain normal. Paralysis of this kind is known as the central or supra- nuclear type of facial palsy. The explanation of the difference between the peripheral and central types of facial paralysis is that the cells in the facial nucleus supplying the upper facial muscles receive vohtional control from both sides of the motor cortex, while the part which supphes the middle and lower facial muscles receives volitional control from the opposite side of the cortex only. A lesion in the pallio-nuclear connection of the seventh nerve would thus cause a paralysis of the middle and lower facial muscles of the opposite side. But since the nucleus is still receiving impulses from the other palho-cortical connection for the upper facial muscles, these latter remain under the con- trol of the will. Splanchnic Sensory Functions of the Pons. The pons receives, by way of the pars intermedia of Wrisberg, the most cephalic fibers entering into the nucleus fasciculus solitarius. These fibers supply the sense of taste to the anterior two-thirds of the tongue. Somatic Motor Functions of the Pons. Through the nucleus abducens, the pons innervates the external rectus muscle of the eye-ball. The nucleus supplying this muscle is, perhaps, the most important nuclear center in the control of the oculomotor mechanism. It takes importance from the fact that it is the pace-maker of eye movements, especially those in the horizontal plane. Somatic Sensory Functions of the Pons. Through the large sensory nucleus which constitutes the cephalic portion of the substantia gelatinosa, whose caudal continuation extends into the medulla and the spinal cord, the pons innervates a portion of the front of the head, the face, part of the external ear, the nose and nasal cavity, the eye and orbit, the palate and nasopharynx in part, the tonsil, the cavity of the mouth, the tongue and a considerable portion of the dura mater fining the cranial cavity. The pons also contains relay stations in the formation of the secondary tracts in the auditory pathway. These relay stations are found in the supe- rior ohvary nucleus and the nucleus trapezoideus. The vestibular division of the eighth nerve receives part of its relay in the pons Varolii. Simple Reflexes Mediated Through the Pons. 1. The Mandibular Reflex. This reflex is ehcited by percussion over the chin, producing eleva- tion of the lower jaw. The reflex depends upon an arc whose afferent arm is in the trigeminal nerve. The nucleus of reception is in the substantia gelatinosa, from which impulses are transmitted to the nucleus masticator- 2US whose efferent arm is the motor division of the trigeminal nerve. 2. The Zygomatic Reflex. This reflex of the lower jaw is ehcited by per- cussion over the zj-goma, which causes lateral motion to the same side. The reflex depends upon an arc whose afferent arm is in the trigeminal nerve. It is relayed in the substantia gelatinosa and connected by reflex collaterals 380 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM -Agueductol Sylvius -CentialGrav^taller -Rubrospinal Tract -Levelof Islhmus r;r.5 Com.Tor. PaTfiway Fi< . 283. — The nibro-spinal tract passing through the pons VaroHi and representing the pontile diA'ision of the striato- niliro-spinal pathway for the condtiction of impulses necessary to aiitoniatic associated control of the somatic muscles. THE PONS VAEOLII 387 to the nucleus masticatorius. Its efferent arm is the motor portion of the fifth nerve bearing the motor impulses to the rnasseter and temporal muscles of the same side. 3. The Nasal Reflex oj Bechtercw. This reflex is elicited by tickling the mucosa of the nasal cavity with a feather or piece of paper which causes the contraction of the facial muscles upon the same side of the face. The reflex depends upon an arc whose afferent arm is in the trigeminal nerve, which bears the impulses to the substantia gelatinosa, transmitting them, by means of reflex collaterals, to the facial nucleus whose efferent arm, the facial nerve, brings the impulses to the muscles of expression of the same side. 4. The Supra-Orbital Reflex oj McCarthy. This reflex is elicited by per- cussion over the supra-orbital ridge, which causes the closure of the eyelid upon the same side. The reflex depends upon an arc whose afferent arm is in the trigeminal nerve, which conveys the impulse to the substantia gela- tinosa, from which it is transmitted by reflex collaterals to the nucleus of the facial nerve whose efferent arm, the facial nerve, conveys the impulse to the orbicularis palpebrarum. •5. The Conjunctival Reflex. This reflex is elicited by touching the con- junctiva over the cornea, which causes the closure of the eye-hd of the same side. The reflex depends upon an arc whose afferent arm is in the trigeminal nerve, which conveys the impulse to the substantia gelatinosa, whence it is transmitted to the nucleus of the facial nerve whose efferent arm, the facial nerve, conveys the impulse to the orbicularis palpebrarum muscle. 6. The Lachrymal Reflex. This reflex is elicited by touching the con- junctiva over the cornea, which causes the secretion of tears. The reflex depends upon an arc whose afferent arm is in the trigeminal nerve, which conveys the impulse to the substantia gelatinosa, whence it is transmitted to the cells controlling the glandular eft'ector activities of the lachiymal gland. The efl'erent arm of the arc is probably through the great superficial petrosal nerve, which, after passing through the Vidian canal, comes into relation with the spheno-palatine ganglion and from that point reaches the lachr3rmal branch of the ophthalmic division of the fifth nerve. 7. The Conjunctivo-Mandibular Reflex. This reflex is elicited by touching the conjunctiva over the cornea, which causes a drawing of the lower jaw toward the side of the stimulation. The reflex depends upon an arc whose afferent arm is in the trigeminal nerve, which conveys the sensory impulse to the substantia gelatinosa, whence it is transmitted by reflex collaterals to the nucleus masticatorius of the same side. The efl'erent arm of this reflex is in the motor portion of the trigeminal nerve. 8. The Auditory Reflex. This reflex isehcited by any sudden sound which causes a momentary closure of both eyehds. The reflex depends upon an arc whose afferent arm is in the cochlear division of the eighth nerve, which conveys the sensory impulses to the general receiving station of the cochlear division, and then transmits them by reflex collaterals to the nucleus of the facial nerve whose fibers form the efferent arm to distribute the motor im- 388 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Agueductol Sylvius Rubrospinal Tract DecuS6ation of Superior Cerebellar Peduncle ■Superior Cerebellar Peduricle evel-of Isthmus Superior Cere- bel lar Peduncle RuDrospinalTract Mesioinilei Interior Olive Pyi'amid rinal Co^r':n Painwgy Fig. 284. — The rubro-spinal tract passing through tlie pon.s. The origin of the superior cerebellar peduncle is also shown. These two tracts repre- sent the cerebello- spinal pathway for the conduction of impulses necessary to the syner- gic control of the soma- tic muscles. THE PONS VAROLII 389 pulses to the orbicularis palpebrarum. Extension of this reflex, probably through the reticular formation, produces a change in respiration resulting in momentary inhibition. A further spread so influences the general body musculature as to bring the individual to a sudden standstill or to hold the body immobile for the instant. 9. The Audito-Oculogyric Reflex. This reflex is elicited by a sudden noise which causes a turning of both eyes in the direction of the sound. The reflex depends upon an arc whose afferent arm is in the cochlear division of the eighth nerve, which conveys the auditory impulses to the receiving station of the cochlear nerve, whence it is transmitted by reflex collaterals from the superior olivary nucleus to the abducens nucleus. These collaterals constitute the peduncle oj the superior olive, and form a connection between the superior olivary nucleus and the sixth nerve. The efferent arm of the arc is in the fibers of the abducens nerve, which conveys the motor impulse to the external rectus muscle of the same side, and also to the opposite in- ternal rectus muscle by means of the fasciculus longitudinalis posterior, thus producing a movement of lateral gaze in the direction of the sound. The Pons in its Relation to Special Functions. Inasmuch as the pons is an auxiliary to the medulla in its tegmental portion, it serves in this capacity to the functions of respiration, phonation, deglutition and secretion. It does not, however, take part in the more exclusively vagal functions of the medulla, that is to say, in cardio-vascular control, or in the regulation of the gastro-intestinal canal. The Pons in its Relation to Respiration. By means of the tri- geminal and facial nerves, the pons innervates the muscles which act in conjunction with the respiratory mechanism in order to prepare the upper air passages for the reception of the inspired air and the delivery of the expired air. In ordinary respiration, the pons, through the fifth nerve, closes the mouth by drawing the lower jaw upward and bjr a slight compres- sion of the lips which is eflected through the facial nerve. In this wa}' it prepares the upper respiratory passage for inspiration, causing the inspired air to pass in through the nose, in order that it may be sufliciently warmed and partiafly dehydrated if the atmosphere is chflly or humid. In active res- piration, when the nasal passage is not sufficient to admit the volume of air required, this process is reversed, the mouth is held open by the fifth nerve and the anterior nares are dilated by the seventh nerve ; so that the pons regulates the intake of air according to the needs of the individual. In extremes of respiratory necessit)^ where there is marked dyspnea and gasping for air, the mouth is forcibly opened by depression of thp lower jaw and tongue, while the anterior nares are distended to their full extent. This wide opening of the mouth in the ePort of respiration resembles in many respects the respiratory activities carried on by the fish in its ordinary efforts to produce a circulation of water through the mouth and into the gills, each respiratory effort being attended by a marked depression of the lower jaw. This same action is observed during dyspnea, and is especially noticed in patients in extremis who, for a short time before death, show a 390 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Laleral Fillet Decussation of Superior Cere- ' ellar Peduncle Mesial nilet Caudal Level of Micfbrain rascicuius Lono- itud malls Posterior Cephalic Level of Pons rriQemi Nerve Auditorv Nerve Inferior Cere- bellar Peduncle Caudal Level of 1hePon5 Mesial nilef pYramidal fasciculi Tecto-spmal Tract Fasciculus LonQifud- n all's Posterior Fasciculus Solilarius Central Grav Matter "AudJtonv Nerve Substantia Gelatinosa Trigemmi Inferior Olive PYramida! Tract finsi CommonPatrrrtff/ -V^Tirrjl GraK ColumnCell' nndl Common Palllw^ . 285. — The fiisciculus longitudinalis pos- terior and the tecto- spinal tracts. This represents the pas- sage of the tracts through the pons. The tracts serve fur the conduction of impulses from tlie tectum of the mid- braui and the inter- stitial nucleus of Ca- jal to the ventral gray ci.>Iumn cells of the cervical seg- ments of the spinal cord and between the nuclei of the oculo-niotor mech- anism. They fur- tluT serve as a part of the protective mechanism against excessive light im- pulses and other pos- sible injuries. The fasciculus longitudi- nalis posterior con- tains both ascending and descending fi- bers. THE PONS VAROLII 391 distinct depressor movement of the lower jaw as tire accompaniment of each respiratory movement. This depressor movement of the jaw continues even after all other respiratory action has ceased, a fact which seems to indicate that the mandibular movement observed prior to death is the persistence of one of the most primitive acts inherent in the respiratory mechanism. The Pons in its Relation to Phonation. The pons innervates muscle groups which serve to mochfy the production of voice sound by movements of the jaws and lips. This modification of the voice is especially witnessed in the effects of mandibular and labial movements in speech, but it is also to be observed in all animals capable of phonation. The Pons in its Relation to Deglutition. The pons serves to innervate the muscles of mastication. But this is not an act of the mastica- tory muscles alone; it is dependent upon the comljination of several nuclei situated in the pons, and also one in the medulla. The masticatory act is dependent upon the temporal and masseter muscles which press the lower jaw upward against the upper jaw, and thus approximate the upper and lower sets of teeth. In addition to this upward movement of the lower jaw, the pterygoid muscles, also supplied from the nucleus masticatorius, produce a grinding motion so that the food between the teeth may be sub- divided and prepared for permeation by the secretion from the salivary glands. During this act of chewing, it is necessary that the food be held in the proper position between the teeth, otherwise it would escape under pressure applied by the masticatorj- muscles and move out either into the vestibule of the mouth or remain in contact with the tongue. For these reasons each movement producing an occlusion of the teeth is accompanied by a compression of the cheek which momentarily obliterates the vestibular space of the mouth and thus prevents food from slipping into this lateral pouch. Simultaneously, the tongue is firmly pressed against the hard palate and thus obliterates for the moment the mouth cavity. These two acts, therefore, synchronized with the occlusion of the teeth, prevent the food from finding any available space along either the outer or inner sur- face of the teeth. When the facial muscles of one side are paralyzed so that the vestibule is not properly obliterated, food escapes on each attempt at mastication from the paralyzed angle of the mouth. Also when the tongue is paralj'zed, the food is not properly held Ijctween the teeth and mastication becomes difficult. The act of chewing, therefore, is a combina- tion of movements causing the occlusion of the teeth and the oblitera- tion of the vestibule and mouth cavity ])roper. To these acts should also be added one which produces a depression of the lower jaw in prepara- tion for each successive occlusion of the teeth under the action of the tem- poral and masseter muscles. This depression is performed mainly by the mylohyoid and the anterior belly of the digastric muscles. The pons also innervates the muscles acting in the first phase of swaUow- ing, which force the Ijolus of food, when properly prepared by mastication and permeated by sahvary secretion, out of the mouth into the pharynx. This is accomplished by pressure of the tongue against the hard palate, by 392 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Aqueduct ofSYlvius Decussalion of Superior Cerebellar Peduncle C enl ral Gray Mailer Laleral rniet Caudal Level of Midbrain nilet TriQeTninalNt Pvrsinidal Tasciculi Dentate .Nucleus Superior Cerebellar Peduncle Cephalic Level of '^ons Mesial Piliet AuditorY Nerve rourlh Ventrict Denlale Nucleus yeslibular Nuclei Caudal Leve) ,of Pons Inferior ^Cerebellar Peduncle. Subsla^nlia Gelatmosa Triaeminr PYramiddl rasciculi Mesial nilet Inferior Cerebellar Peduncle — N y Cephalic ^ W'entricular Level :rM\of Medulla l,^:;:?.-' I Inferior uh^ye P\'raiTiici ,Soniae5thetic Semor>'Are3 of Corlex --VSuperioT Tholamtc peduncle Fig. 286.— The mesial fillet passing through the pons and representing the pontile division of the spino-thalamo-cor- tical pathway. The tracts serve for the con- dnction of discrimina- tive som esthetic im- pulses from the skin, muscles, joints and bones. THE PONS VAROLII 393 closure of the lips and by compression of the cheeks in such a way as to obliterate momentarily the vestibule of the mouth. The combination of these acts depends upon nerve impulses received from the pons Varolii. The Pons in its Relation to Secretion. Through the trigeminal nerve the pons innervates the sublingual and submaxillary glands from the nucleus salivatorius superior. It also innervates the sebaceous and sudori- ferous glands of the face and fore part of the head and probably the lachry- mal glands. The Pons in its Relation to Eye Movements and Hearing. Through the nucleus of the sixth nerve, the pons innervates the external rectus muscle of the eye-ball. As already mentioned, this muscle serves as the pace-maker of all movements of lateral gaze. For this reason, the pons becomes one of the chief elements in the brain-stem controlling movements of the eyes. The greater number of oculogyric paralyses are attributable to lesions affecting this part of the brain. The pons is also important as afford- ing relay stations in the secondary tracts of hearing. These relays are found in the nucleus of the superior olive and the nucleus trapezoideus. The pontile nuclei, which constitute a large part of the massive structure of the pons, are recent acquisitions by the brain-stem. Their function is the relaying of impulses from the cerebral cortex to the cerebellum, thus bringing these two parts of the central nervous sj^stem into intimate relation for the purposes of synergic control in the regulation of skilled movements. FUNCTIONS of THE WHITE MATTER OF THE PONS As is the case in the medulla oblongata, so with the pons, continuity in the conduction paths of the brain-stem is afforded by this division of the brain. Bot'h ascending and descending tracts pass through the pons. Most of these have been encountered in the preceding segments; but in several instances new elements in the white matter have made their appearance. Descending Tracts Traversing the Pons. The descending tracts which pass through the pons consist of those already described in the medulla oblongata. The pyramidal fibers occupy a different position from those in any other part of the brain-stem, and have an arrangement which is characteristic of the pontile levels only. The pyramidal system, instead of being a solid, collected mass of fibers as in the medulla, consists of a number of fasciculi separated into bundles by the transverse fibers of the stratum complexum of the pons. The pyramidal fibers now occupy a position in the basis. The ventral shift of these fibers is due to the interposition of the stratum pro- fundum pontis between the pyramidal tract and the tegmentum. The actual boundary between the tegmentum and the pontile basis is the mesial fillet, whose ventral border is contiguous with the stratum profundum pontis. The tectospinal tract is also found in the pons occupying its former close relation with the jasciculus lojigitudinalis posterior. The rubrospinal tract lies in a position dorso-lateral to the superior olive. 394 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Lateral niiet Decussation of the Superior Cerebellar Peduncle Mesial nilet Caudal Level of tlie i^idbiain Spino-ttialamicTract Superior Cerebellar Peduncle Mesial fillet Cephalic Level of the Pons Pyrainidal fasciculi Dentate t\Jucleus nferior Cere- bellar Peduncle Caudal Level 'of the Pons SpinoThalamic Tract Central Gray Matter Auditorv Nerve Inferior Cerebellar Peduncle Substantia elatmosa TriQemini Cephalic Ventricular Level of I^^edulla nlerior Olive Pyramidal Tract FiG.'-S". — The spino-thala- luic tract passing i'lrough the pons and rcpresentinf; the pontile division of the spino- thalamo-cortical path- way. Tins tract serves to conduct impulses of affective sensibility, pain, discomfort and temperature. It is called the spinal tillet because it undergoes complete di'cussation m the spi- nal cord. THE PONS VAROLII 395 ^Queduct of SyIvius Lateral nilet- Mesial Fillet Caudal level of Midbrain Posterior Long- itudinal rasciculas Decussation of Superior Cere- be liar Peduncle -Ventral Spino- cerebellar Tract Superior Cerebellar Peduncle Mesial Fillet Cephalic Ventricular Level of Medulla /r^_r-': ,i^^=x\rMesial fillet CS^;;r\lnferior Olive pyramid CereDellum rerfninjtlon of Ventral Spino- cerebellar rracl Fig. 288.— The ventral and dorsal spino-cerebellar tracts. The ventral tract passes into the oerp- hellum by way of the inferior cerebellar ped- uncle at the upper level of the medulla. The dtirsal tract passes through the pons and part of the midbrain. It turns directly back- ward along the superior cerebellar peduncle to terminate in the cere- bellum. These tracts are part of the mech- anism \'i'hich is ac- tive in the synergic control of the muscles. y u% ■./t \' 396 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM The central tegmental tract occupies its usual position near the center of the reticidar formation. The jasciculus dorsalis longitudinalis oj Schiitz still holds its place in the central gray matter subjacent to the floor of the fourth ventricle. The reticular j ormation, while not so rich in gray matter, consists of the large formatio reticularis alba, in which are many descending fibers inti- mately connected with the splanchnic functions. The Ascending Tracts Traversing the Pons. The ascending tracts in the pons likewise show Init slight addition to their representation as seen in the medulla. The vtesial fillet is present but somewhat altered in its relation and position. It now extends transversely across the neuraxis forming the bound- ary between the tegmentum and pontile basis. This shift into a ventral posi- tion is consequent upon the removal of the pyramidal system out of relation with the tegmentum into the basis. The spino-thalamic tract lies ventral to the rubrospinal tract and mesial to the ventral spino-cerebellar tract. The Deitero-spinal tracts have already consummated their connection with the vestibular nuclei and consequently do not appear in the pontile levels. A few fibers of the ventral Deitero-spinal tract may occasionally be observed in the caudal levels of the pons. The fasciculus longitudinalis posterior occupies its usual position subja- cent to the floor of the fourth ventricle, mesial to the nucleus of the sixth nerve and ventral to the nucleus incertus and nucleus funiculi teretis. One tract, the latered fillet, a secondary connection in the cochlear path- way, has made its appearance in the pons. It is formed by fibers which have undergone decussation in the trapezoid crossing, or have reached the secondarj' stage in their course after decussating either in the floor of the fourth ventricle or immediately below it. This tract occupies a position lateral and adjacent to the mesial fillet. It serves to convey auditory im- pulses to tlie brain. At this level, three distinct fillet systems are discernible; First, the spinal fillet, consisting of a sensory pathway which has undergone decussa- tion in the spinal cord antl ascends into the medulla and through the pons as the spino-thalamic tract. 8(K'ond, the bulbar or mesial fillet, which has undergone decussation in the medulla; after crossing it has ascended through the remainder of the medulla and pons as the mesial fillet. Third, the pontile or lateral fidlet, which after decussation in the pons becomes a collected bundle ascending in a position lateral to the mesial fillet. xVll of these afferent tracts serve as parts of sensory pathways; the spino-thalamic tract for the purposes of pain-temperature conduction; the mesial fillet for the purpose of tlie conduction of critical somesthetic sensibility, and the lateral fillet for the purposes of auditory conduction. Decussations in the Pons. Two major decussations take place in the pons. The largest and nujst important of these is the pontile decussation consummated through tlie transverse fibers of the pons and serving to estab- lish a crossed connection between the cerebral cortex and the lateral lobe THE PONS VAKOLII 397 of the cerebellum. The fibers of this decussation are found in three layers, the stratum superficiale, the stratum profundum and the stratum com- plexum. Each fiber in the decussation is relayed in the pontile nuclei before it crosses the midline to enter into the formation of the opposite middle cerebellar peduncle. The purpose of this decussation and the communica- tion which it establishes are in the interest of synergic control in skilled movements. The second decussation of the pons is the cochlear or trapezoid decussa- tion which takes place in the tegmental portion of the hindbrain in intimate relation with the mesial fillet. This decussation affords a crossing in the auditory path which, after the fibers have decussated, is constituted as the lateral fillet, a secondary auditory tract on the way toward the cerebral hemispheres. PRIiVCIPAL SYNDROMES OF THE PONS VAROLII As in the medulla, lesions in the pons resulting from disease or injury seldom confine themselves to either the gray or the white matter, but involve some part of both of these elements simultaneously. Only the more frequent and illustrative symptom-complexes arising as the result of involvement of the pons will be considered in the following descriptions: Syndrome of the Head and Eye-Turning Contingent of the Aberrant Pyramidal System. History. A child, four years old, had complained of frequent headaches for five weeks. He was listless and fretful most of this time. There was a slight, irregular rise in temperature during the latter part of his illness. His parents noticed that both eyes were drawn toward the right and that he seemed unable to move his eyes toward the left. His head was also turned so that the chin pointed toward the right. The von Pirquet test was positive. The temperature rose gradually for several days, and after a bronchopneumonia lasting five days, he died. Examination. At the onset of his oculomotor symptoms, examination showed the following: The sotnatic motor com-ponent, with the exception of the oculomotor paralysis, was normal in all particulars. IcHodynainic, reflex, tonic, voli- tional, synergic and associated automatic control were normal. There was a paralysis of the left external and right internal recti muscles of the eyes, giving rise to a paralysis of left lateral gaze (levogyric ocular paralysis) which produced a right conjugate deviation. The intrinsic muscles of the eyes were normal. The somatic sensory component was normal. The splanchnic motor component showed a paralysis of the right sterno- cleido-mastoid and trapezius muscles which resulted in a dextrocephalogyric paralysis, so that the head was turned in such a way that the chin pointed toward the right under the action of the unopposed levocephalogyric muscles. In other respects the splanchnic motor control was normal. The splanchnic sensory control was normal. 398 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Interpretation and Anatomical Analysis. Evidence of the focus of the lesion shows that the pathological process was situated in such a position that it involved the oculogyric and cephalogyric fibers of the right side. Such a focus exists near the cephalic limit of the pons. Here the pontile aberrant pyramidal contingent is still isolated between the fillet and pyra- midal system. The evidence of circumscription of the lesion is afforded by the absence of all other somatic and splanchnic motor and sensory disturbances. Fig. 289. — A and A'. Syiidrume of the head and eye- tnrning fibers of the alierrant pyramidal contingent: syndrome of paralysis of lateral gaze; syndrome of FoviUc. Blue indicates paraly,sis of the sterno- cleido-mast(jid and trapezius muscles. There is also a right conjugate deviation. C. Cro.ss section through the jjiins showing the location of the lesion in the xyndroiiie of Fovillf (paralysis of lateral gaze): involvement of the pontile oculo- ceiihalogyric contingent of tlie aberrant pyramidal SNStl'Ul. DrvGNosis ANr) Pathology. The diagnosis in this case is a tuberculoma of the pons on the left side. The actual lesion discovered was about the size of a small pea. Nomenclature. This is the snitdromc oj paralysis o) lateral gaze: it is also called the synclro-me oj Fanllc. Summary. The essential clinical features of the syndrome of Foville are: f. Paralysis of lateral gaze contralateral to the lesion producing ipsi- lateral cc^n jugate deviation of the eyes. THE POWS VAROLII 399 2. Paralysis of lateral rotation of the head contralateral to the lesion producing ipsilateral deviation of the head. 3. The absence of all other sensory and motor symptoms. Syndrome of the Pyramid and the Oculogyric Aberrant Pyramidal System. Htstoht. a man, sixtj^-seven years of age who had suffered fi'om the effects of prolonged high blood pressure and nephritis, had an apoplectic seizure. Upon recovering from the acute stage it was found that he had a left hemiplegia and a paralysis of left lateral gaze with right conjugate Fig. 290.— .1 and B. Syndrom(3 of tlie iivramidia triict, and the oculog3'ric_ aberrant pyramidal system. Syndrome of hemiplegia comliined "witli poralj'sis of lateral gaze. Hemiplegia with the syndrome of Foville. Red indicates au upper motor neurone paralysis with the appearance of pathological re- flexes. There is also a right conjugate deviation. C. Cross section through pons showing the location of the lesion in the syndrome of hemiplegia com- bined with paralysis «f alteral gaze: involvement of pyramidal tract and the pontile oculogyric contin- gent ol the aberrant .pyramidal system. deviation of the eyes. Several months after his initial seizure he had a second apoplectic attack in which he died. ExAMiXATiOX. Upon examination after his first seizure, he presented the following : The somatic motor component sliowed idiod3'namic control in all move- ments of the body normal. The deep reflexes of the left side were all more active than those of the right side. There was a Babinski and ankle clonus on the left but none on the right. The muscle tone of the left side was in- 400 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM creased as compared with that on the right. VoUtional control was lost in the left arm and leg and m these parts abnormal associated movements were observed. Equilibratory and synergic control could not be judged on the left side because of the paralyses, but elsewhere were normal. There was a paralysis of left lateral gaze involving both eyes and the head. The patient could not look to the left, and the eyes were held in right conjugate devia- tion. The head was turned so that the chin pointed to the right. The somatic sensory component was normal. The splanchnic motor component was normal. The splanchnic sensory component wa.s normal. Lnterpretation and Anatomical Analysis. The nature of the lesion was a vascular accident, in all probability a hemorrhage, because of the history of prolonged high blood pressure, the nephritis and the two apoplectic seizures. Evidence of the focus of the lesion resulting from the first apoplectic attack is given in the simultaneous involvement of the right pyramidal sj's- tem and the aberrant pyramidal fibers serving for oculogyric and ccphalo- gyric movements. Such a region is to be found in the pons near its cephalic extremity, where the aberrant fibers which have left their pyramidal associa- tion are passing obliquely backward toward the mesial fillet. In this region they lie in the stratum profunduin between the fillet and the pyramidal tracts. The evidence of circumscription of the lesion is given by the absence of all other sensory and motor symptoms. DiAONOsis AND Pathology. The diagnosis of this case is hemorrhage in the pons near its cephalic extremity upon the right side. Nomenclature. This is the syndrome oj hemiplegia combined with paralysis of lateral gaze. It is als(.) known as hemiplegia, with the syndrome ofFoville. SuMM.\RY. The essential clinical features of hemiplegia with the sjti- drome of Foville are: 1. Hemiplegia contralateral to the lesion. 2. Paralysis of lateral gaze contralateral to the lesion. 3. The absence of all other sensory and motor symptoms. Syndrome of the Mesial Fillet, the Pyramidal and the Oculogyric Aberrant Pyramidal Systems. History. A married woman, forty-one years of age, who had had four miscarriages and one still-born child, suddenly and with- out premonitory symptoms developed a partial hemiplegia of the right side. She was unable to look to the right, anil the eyes were turned in such a way that they were held turned toward the extreme left. In the course of several weeks she lost tactile sensibility in the right arm and leg and the right side of the body up to the interauricular line. Muscle, joint and vibratory sen- sibility were also defective in these areas. The Wassermann reaction in the blood and spinal fluid was ])ositivt'. After a course of intensive antiluetic treatment she made a complete I'ccovery. THE P<)N« VAROLII 401 Ex^uiiNATiON. Wlieu exMnunecl shortly aftc the appe^iranfc of the right hemiplegia, slio nuuiil'csted the following: The sornaUc viotor compone-nt showed that the idiodynamic control of the entire musculature of the body was normal. All the reflexes on the ri"ht side Avere more active than those ou the left. There was a right-sided Bab- inski and ankle clonus. The right alxlonunal reflexes were absent The tone of the muscles in the i-j-ht arm and le- was increased f,ver that upon the t'l 11. 291. — .1 ;ui(l Ji. Syiiflroiiic ,,[ the mesial fillet, |)yi-:i.ii]i(liil tr;ict iiiirl tlio oculogync aberrant py- I'aiiiiil.-il system. Hyiidi-oine of liemi;me.sthetic hemi- lilcffiii C(jml)iiie(l witti {he .syndrome oi' Foville. Keil iiiilieates an iipijor motor neurone paralysis \vitli (he a.i)])earance of abmirmal associated move- menls and ))a(li(jlogiraL reflexes. Also a hemi- anesl ln'sia. alfeetmg discriminative .sensibility. J)lue indicates a liemianesthesia affeetinn; dis- eriuiiMa.li\"e sensiliiljtv. TtKM-e is also a left ennjugate deviation. f'ro.ss section throiisli tlie jjoils showmg the location of the lesion in the :-:i/iulronic nf hemianesthelic liriiiiiili ijid niiiihinr:! irith. n pririil ijxla of Inlcrnl gnzr: in\'olvciiient of p\'raniiJal tract, njesial fillel. and oiadogyric (■(■ntingiait nf aberrant pyramidal system. left Side. Wjlitional control m the right ai'ni and Ice- was much diminishetl. Equilibratory and synergic control on the right side were difficult to estimate because of the paral3'sis. (..)n the left side coordination was normal. Abnormal associated movements were present in the right arm and leg. With the ex- ception of the (lord .■iiid si\lh nerves, ihc cr.'initd nery-cs were normal. There wa.s a marked paralysis of Ihc rij^ht (external rectus tind lid't internal rec- tus. This defect gave rise lo a paralysis nf ri^lil hitei'al gaze which resulted 26 402 FORM AND FrN('TI(INS OF THE CENTRAL NERVOFS SYSTEM in a left conjugate deviation, the eyes being drawn over by the unopposed antagonists to the side opposite the paralysis. The somatic sensory component showed a hemianesthesia of the dis- criminative type on the right side of the body exclusive of the head and face, ventral to the interauricular line. All other cjualities of sensibility were normal. The left side of the body showed no sensory defect. The Sphmclmic Motor Component. With the e.xception of the paralysis (if the cephal()g_yric muscles causing a paralysis of de.xtrogyric head move- ments, there were no disturbances in this component. The sjihmchnic sen.sorij component was normal. Interpretation and Anatomical An.ilysis. The lesion was due to syphilis, as shown by the Wassermann test and the ready response to antiluetic treatment. Evidence of the focus of the lesion is given by the simultaneous involve- ment of the pj'ramid, the fillet and the aberrant oculogyric and cephalogyric pyramidal sj'stems. Such an involvement might be tlctermined by a lesion in the cephalic portion of the pons atl'ecting the basis and tegmentum. Evidence of circumscription of the lesion is furnished by the absence of all other motor or sensor}^ symptoms. DiACiNOsis AND P.'lThology. The diagnosis of this case is a vascidor type oj nairosypJiilis involving the cephalic portion of the pons on the left side. Nomenclature. This is the syrulrome oj hemianesthetic hemiplegia combined inith, the syndrome oj Foville. Summary. The essential clinical features of the syndrome of hemianes- thetic hemiplegia with the syndrome of Foville are: 1. Upper motor hemiiilegia contralateral to the lesion, 2. Hemianesthesia of the discriminative type contralateral to the lesion. 3. Oculogyric paralysis contralateral to the lesion, producing conjugate deviation ipsilateral with the lesion. 4. Cephalogyric paralysis contralateral to the lesion, producing cepha- logyric deviation ipsilateral with the lesion. .5. Absence of all other motor and sensory symptoms. The Syndrome of the Pyramidal System and the Emergent Fibers of the Abducens Nerve. History. A man, thirtA'-eiglit years of age, who was eni]iliiyed as an insi)ector of gas mains, became unconscious while making an examination in a poorly ventilated conduit into which much illuminating gas had escaped. After being carried into the air he re- mained unconscious and stiqiorous for several ihiys. ^^'hell he regained sufhcient consciousness to make examination possible it was found that he was suffering from a left hemiplegia and a paralysis of the right ex- Icinal icclus wliicli gaA'c him an inteinal strabisnuis of the right eye with diplopia (double vision). 4'lii' subseiiuent course of events in this patient's case was of considerable iiilciest, as he icmaincd in the hospital for fifteen weeks, and was an im'alid una1)le to return to work for a j'ear and a half. At the end iif tliis time he had made a fair recoverv and was assigned to THE PONS VAROLII 403 work which, however, did not call upon him for further exposure to illumi- nating gas. Examination. Examination was made when he regained consciousness after his exposure to the gas. The somatic motor mmponent showed that there was normal idiodynamic control of all the musculature of the body. The deep reflexes on the left side were all more active than the right; there was a left ankle clonus and a left Babmskx. There was an absence of the abdomintil reflexes on the left. The Fig 292. — A and B. Syndrome of the pj-raniidal tract and the emergent fibers of the abducens nerve. S3rndromc of abducens alternating hemiplegia. Syndrome of Millard-Giibler. Red indicates an upper motor neurone paralysis with the appearance of abnormal associated movements and patho- logical reflexes. There is- a right internal strabismus. Cross section through the pons showing the posi- tion of the lesion in the syndrome, of Millard- Gubler: Involvement of the pyramidal tract and emergent fibers of the abducens nerve. muscle tone of the left side was distinctlj- increased as compared with that of the right side. The volitional control of the left side of the bodj' was defective so that the patient had verjr little voluntary movement in the left arm and leg. There were definite abnormal associated movements in the left arm and leg and none on the right side. Synergic'and equilibratory control could not be judged in the left arm and leg because of the existing paralysis, although they were normal in all other parts of the body. The right external rectus muscle was paralyzed, indicating an inA'olveracnt of the right alxlu- cens nerve. All of the other cranial nerves were normal. 404 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM Till' sDiiKilii- .N' iisiirij I'oiiijxiiiriil sliiiwcd iKi delect. The Kjilitiirliiiir iiKilor i-iiiii jiiininl was iiniiual. Tlie Hjildiii-hiiic Kcvsorii nuii jidiiiiiI was noriiial. L\Ti;ui'Ki;rATi()X axd Axathmkal Analysis. Tlie nature of this lesion \\as a tliidinlxisis I'esiill in"ric fillers, in w liicli ease (his t^'])e ol' a! I erieit inu hemi|ile;;ia would lie I'omplicatcd 1 ly an aiics- tliesia of the oppiisite side, eomliincd with ihe syndrome of Fox-ille. Sr.M.MAin. 4'he esseiit lal elinical features of the syndrome of abducens allernal inii; lieiiiiplegia (s.\'ndriime of Millard-CUibler) are: 1. }Ienii]ilei^i,'i contralateral to the lesion. L'. In\-ol\ eiiieiit of the al idiieeii.-; ner\-i' causing ipsilateral paralysis of (he external reetiis wi(li internal siraliisiims and diplopia.. 3. 4"lir alisence of all other motor .-ind sensory sym|)(-sis of tlie left arm and leg was not complete, so that it was jjossible to discern a certain degree of ataxia in them. The |)atii'nt survived the de\'elo))ment of these brain ,s3'mi)toms i'or several weeks, l)ut finally succumlied suddenly as the i-esult of pulmonrii>' embolism. t~iG. 29?..- .1 anil il SxiKJronir iif llic iiMaiiud, fillrt, inferior cciitjcllav peduncle and pii.-^tcriur longi- tudinal fascirulus: pontile s>-ndnimc iit Raynioiid- (.'cKtnii. Red nnlicates an iijipcr motor siourone pai-alvsis with ahnoiinal assoriatf-d movements. ]iatliolo|j;i(':d reflexes ami an a^^•nerl>;ia witli a loss ot sensiliilit,\-. Blue mdirales a loss of dis- eiimin.'itna- .m^usM jditx". ttreeu indieates a partuil jiarah'sis of the sterno-idcido-mast(jid and trapezius muselrs. Tliere is p. right eonjugate (k'\iatioii with dissi>riatioii of the e>-e-iu()vements. I'. Ci'oss sertion through tlie pons showing t lie location of the lesion in the /)e;,///c xi/i,Jruiiir ,if Riiijnioinl- Ci:j the pons Varolii. N(>MENCLATr}u:. This is the pontile syndrome oj Raymond-Cestan. Summary. Tlie esscutnil clinical features of the pontile syndrome of Raymond-Cestan are: 1. Hemiplegia contralateral to the lesion. 2. Hemianesthesia contralateral to the lesion. 3. ContraIat(_'ral oculogyric j^aralysis with dissociation of the eye move- ments giving rise to a transitory diplopia. 4. Hemiasjmergia ipsilateral with the lesion. .5. The aljscnce of all (filler motor and sensory symptoms. CHAPTER XXIII THE CEREBELLUM A GENERAL VIEW OF ITS EVOLUTIONAL SIGNIFICANCE A Suprasegmental Portion of the Nervous System. The cerebellum, or "httle brain," is the expanded dorsal portion of the metencephalon. In mammals it is next in point of size to the cerebral hemispheres, from which it is separated by a membranous or bony plate, the tentorium cerebelli. In the lower vertebrates the cerebellum, although variable in size, is constant in its general characters. Because of its position above the segmented parts of the neuraxis, it is called suprasegmental. This designation recognizes not only the cerebellar relation to the rest of the central nervous system, but is meant even more to imply a sublimation in this organ of a certain control of special functions over which the cerebellum stands supreme. There are two other suprasegmental structures in the brain besides the cerebellum, the tectum oj the midbrain and the cerebral hemispheres. All of these suprasegmental organs, however, have the same general signiiic- ance; they serve the purposes of some special functions for which the seg- mented portion of the neuraxis in itself does not provide; and they are, by their morphological nature, capable of great expansion where the demands of adaptation recjuire the most complex correlations of nerve impulses. Contrasted with the suprasegmental parts of the brain, the segmental portion of the neuraxis presents a decided inflexibility in its morphological character, and is susceptible of but a small degree of expansion. It was originally endowed with and persistently retains the control of the definitely fixed and fundamental organic reactions. It is the foundation without which a super- structure would be impossible. The ground plan of the segmented portion of the central nervous system in vertebrates is constant. The decisive differences in the form of the brain occur in its suprasegmental parts, and as these latter vary in their degree of development, so animals differ in their range of adaptability to their environment. The cerebellum, like the other suprasegmental organs of the brain, difl'ers from the segmented portions of the neuraxis in certain essential particulars : 1. The cerebellar gray matter forms a cortex surrounding the white matter. This is a reversal of the relation of the graj^ to the white matter in the segmented portion of the nervous sj^stem. Such a position of the cell- containing substance greatly enhances the opportunity for expansion, since the cortex is not hampered, as is the case in the spinal cord and medulla, by a heavy investment of white matter. 2. The cerebellar connection, by means of peripheral nerve fibers, with receptors and effectors of the body, is much less direct than that of the 407 408 FORM AND FX'NCTIONS OF THE CENTRAL XERVOI^S SYSTEM segmented parts. This undoubtedly provides for less inunediate reflex action, but also makes possible a greater degree of coi'relatiou of ner\'e impulses in each cerelxdlar reaction. The Phyletic Constancy of the Cerebellum. The cereljellum is an organ of great antiquity. ]']vcii among uiveitelirates, certain arthropods (crabs), according to Betlie, ha\'e a structure in the central nervous system whose functions appear to be analogous to those of tlie cereljellum. Among vertebrates it is a constant element of the brain, although subject to pro- nounced variations. The \'arial)ility of its devehjpment depends upon a definite I'ule. Those animals which are capable of limited and simple move- ments ])ossess a. small and sim])le I'erebelhim, whereas animals having Fig. 2(1)-. — Dinnitunmatic rc])iosentati(iii of tlie ccrclicll.iin in the vci'toliriite series- flnrsiil view. Dai'kfiicd area. C.-trornyzon lliiiiipn-; : ;ilin\r Srylliuiii i-Hiirula l,li ,L'-fi.^lil br-liiw. a wide range of motor acti\'ity possess a highly de\cloped cerebellum., The organ apjiears in its simplest fo)'m in cyclostomes and amiiliibia, animals whose aclivilies are relatively the most sluggish. A b)rief l'e\-ie\v of the ap|>earanee of the eei'ebellum m the se\'eral classes of vertebi'ales sei-\-es Id emphasize the imiioiiance of tliis ruli'. The Cerebellum in the Different Classes of Vertebrates. In cycJos- totiKs. (lie eerebellum is but little developed; it a|i|>ears as 1 wo slight dorso- lateral e\-agmalions of the me( euceplialon eoiuiected across the fourtll ventrii'le by a central ai'i'hed portion. The niosl conspicuous paiis are the dorso-lat eral evaginatioiis. These are m direct coniKM'tion with 1 h(> somatic sensory ti'acfs and receive some general and sjiecial cutaneous neiA'C fibers. It is probalile that the cerebellum is conn(M'(ed with the guslatoiy sense in THE CEREBELLUM 409 these forms. Histologicalljr, there is evidence of liegiiiniiiK (lifferentiation into the types of cells characteristic of the cei-ebelluni, for certain large cellular elements are prc^sent, both in the dorso-lateral evaginations and in the central arch. Many medium sized nerve-cells are also present and tend to take up positions in a deeper stratum. These cellular elements are doubt- less the forerunners of the Purkinje cells and the cells of the granular layer. Axones from some of the large cells follow a course similar to those seen in secondarjr cutaneous tracts and decussate in the mesencephalon. Johnston believes they may represent fibers in the superior cerebellar peduncle of the higher vertebrates which arise in the dentate nucleus and reach the red nucleus in the midbrain. If such is the case, these large cells themselves Vic. 29,5. — DiaKiaiiiiuatic representation uf the cere>lielliim in the vertebrate series, dorsal view. D.arkeneil area. SiiliMO sal.Tr (salmon) above. Rana cscnliaita ifr..<;) li'-lov, . are the prototypes of the celhdar elements later found in the dentate nucletis. This simple form of cercljenimi corresponds with the sluggish motor habits of the cyclostomes. In selachians (the sharks and rays), the cerclx-llum shows a, marked advance in develoijment ; it c.,nsists of a large arch in the reduplicated ro-.f- plate of the metcncephalon, having many evaginations mto which recesses from the cavity of the fourth ventricle extend. Its greater volume as com- pared with the cvclostcjmes is consequent upon the greatly increased size and complexity of its somatic sensmy ])ortion. Histologically, the organ shows much further s])ecialization tlian in the cA'clostomes. There are many more granular cells, which form a dense, compact ' sim|")le in radrnis, whose loc(.(motion carries them near tlie ground and whese general nnitor ca|)aeity is iidt extensive. In contrast to the rodent, the nirnivores, li(>causc of a locdmotion whicli carries the Ixidy at a distance from tli(> ground, have a more complex cerebellum. The great i)ower of these animals, eitliei' in springing or climbing, makes still furtlier demands u]ion the cerebellum. Tlie iiiKjiiltilcs ha\'e ;iii especialh' well developed cer(4i(.'lluni, ])articularly those wlidse extremdies .'ire lung, such as the camel and gira.''e. In the pro- hos{-/(l/ii, the cei'eliellimi :ittains an exceptidiial size. 4'liis IS the case in ele- ])hants whdse great liddy weiulit, liemg sustaiiie(l and carried at Sdine dis- tance IVdin the grdund, i'e(|iui'es an exteiisi\'e synergic conti'ol to maintain efiuilililiuiii. ('ei'taiij dl llie (iiiuiilif ciiin iron s. inr exaiii|ile t he seals, ha\e a large and highly de\-eld|ie(l ceicliellnni by iiieans df wliicli they ,a]'e enabled to execute tlie cdiiiplex acis iiecessai-y td s\\ iniiiiing and I lie pei'l'drmancc of the swift correlated m(i\-eiiient s di ilie head and tiaiiik by wliiidr they defend them- selves and prd(aire their fudd. But by far (he most. Iiighh' de\'el(i]ied cei'ebellum is seen in tlie prinintes. ddie inilliropo/il (//le.s-, repi'csent ing as they do the transitidii fidm the (.[Uad- iu|ied Id the biped, pdssess a i-dm])lex cerebellum winch, in the main, is THE CEREBELLVM 413 the morphological response to the needs of coordination m arboreal life but which also foreshadows the inception of the process that has freed the upper extremities from responsibility in locomotion. This process has re- sulted in the establishment of a motor organ which eventually has come to have the widest rauRe of motor activity, the human hand and arm. The relative size and complexity of the cerebellum among ilu- diflerent forms of primates are of interest.. Those living a strictly arb.n'eal life show a pronounced development in the vei-ims and the tentorial surfaces of the hemispheres -"••s. — f'crebelluni of mountaiii- coat {Orenmnns inonlaiins]. Vic. 2!lll.— Cereliellum of ,|i)u; (Canix faniilarri:^}. Fig. 300. — Cerebellum of sloth bear (Aldiirsris labiaiiis). Fic, .'JOl. — Cerebellum of ape (Macocus rhef:vs). Those forms in which the biped tendency has made further ath'auce. with the gradual freeing of the upper extremities from tlirect participation in locomo- tion, such as the gnrilla, chimpaiizcp and orong-ovtnng, have a greater degree of development in the occipital surfaces of the hemispheres. This morphologi- cal fact is of much significance, since it is in full accord with the now generallj- accepted conceptions of cerel^ellar localizations. Considering the re(|uirements of such a moliile organ as the human hand and arm, and the demands of synergic control m the jierformance of l)i])ed locomotinn, it is not surprising to find the most highly developed cerebellum in man. 414 FORM AND FUNCTIONS OF THE CENTRAL NERVOI'S SYSTEM Generalized Pattern of the Cerebellum in Mammals. Descriptions of the cerebc41um liave caused much confusion, because they have been based upon the conditions of the most complex of all forms, man. Elliot Smith and Bolk have demonstrated that such divisions as have been employed for the hunuin cerebellum will not meet the reriuirements in the different orders of mannnals. A sim]:ilifiefl scheme for the divisions of this organ has been devised by Elliot Smith and supplemented in a later work by Bolk. Smith's studies were Inised upon the cerebellum in the edentata; those of Bolk were made upon the cerebellum of lemur albifrons. Both investigators recognize an anterior and a posterior cerebellar lobe separated from each other by a large fissure which appears early in development, the fissura prima. The posterior lobe is further subdivided by a second fis.sure Fig. 302. — Cerebellum of cliimpanzee {Troglodytes niger). appearing later in development, ihc Jissura secnn.dii. As growth proceeds, the anterior lolje becomes sulidi\ided l;>y other secondary fissures, i.e., (1) the fissura preculminata and (2) the Jissnra lingulis. These fissures deternune three sulxlivisions in the anterior lobe, the most cephalic of which is the linguhi; the middle, the pars preculminata; and the most caudal, the pars culniinis. The posterior l()l)e shows much more sub- division. In it are rcci)giiiz(Ml a median portion corresponding in position to the vermis, which is di\i(I('(l into four parts by three parallel fis,sures, (1) the fissura suprapyraniniali^, (2) the fissura secuncla, and (3) the fissura prenoilularis. These fissures divide the median portion into the pars supra- 'pyniiii.idall^, 1lic pijraiii.iil, the ariila and tire iiodula. The lateral expansion connecU.'d wi1 h this |)ortion of tlie vermis is divisilile into two parts, the pars lateralis and the pars Jlocciili. The pars lateralis is the lateral expansion of all that i)art of the vermis ce])lialad of the fissura secunda, while the pars THE CEREBELLUM 415 flocculi is the lateral expansion of the nodule and uvula. The pars lateralis is subdivided into eertani smaller areas by the appearance of three radiating fissures which converge upon the vermis. These fissures are the fissura postlunata, the fissura postpteroidea and the fissura parapijramidalis. The area cephalad of the fissura postlunata is the area lunata. Caudal to this in regular succession are the area pteroidea, the area postpteroidea and the areei parapyramidcdis. The pars flocculi is divided by a fissure which extends inward from the lateral extremity about one-third of the distance toward the nodule; this is the fissura floccularis, which separates the paraflocculus from the flocculus. The fissura parafloccularis intervenes between the pars lateralis and pars flocculi. ^^^ __, '"^^^ . ^1. insula \ Area Lunata^ ^y^ ^ , ^\_ t, , -r^ ,-, ■ . ! Lobus Fissura Postlvmata Paraflocculus Fissura Parapyramidalis Fissura Floccularis Culniinis J Fissura Prima Area Ptcruitlca.j Fissura PostpteroideaA^ ^ ^^ :^ J-Pars SupmpyrLinii.laHs Fifisiira Secunda^ Fissura Parafloccularis m._a ~— ~,*^ \ "^ /^ ■ -' Aii'a PostptcToid- Area ParapyraiJiidi'a U^-ula Flocculus Z*^ yf — ■ _ ~~—-- -- — J__ Lobus Po-stcrius Fissura -5^^<,A^v2^>C j^^^ ^""'^ Nodulus Fig. 303. — Schematization of the fundamental arrangement of the parts of the mammalian cerobeUum spread out in one plane, according to Elliot Smith, as a result of his original work on the cerebellum of the edentata. This pattern, according to Elliol 8mith, may fie applied to the analysis of the cerebellum of all vertebrates with the possible exception of the monotremes. Bollv, as the result of a study of the cerebellum in a large compara- tive series, still further advanced the ideas put forward by Elliot Smith. He concluded that the several parts recognizaljle in the mammalian cere- bellum have definite functional significance, and represent areas of central control over definite motor performances in the bod}^ According to Bolk, the cerebellum is divided into an anterior and posterior lobe Ijy the sulcus primarius which corresponds to the fissura. prima of Smith. The anterior lobe is diA'idcd by a series of three fissures into four lobules which Bolk numbers 1, 2, 3, and 4. A small and shallow fissure parallel to the sulcus primarius delimits the lolrulus sim]ili:x, wliich extends fi'om the A'crmis out upon the lateral expansions of the hemispheres. The major portion of the posterior lobe, however, that which lies caudal to the lobulus simplex, is divid(>d inti> a median lobule and \\\o lat(>ral lobules. The median lobule constitutes the vermis and is separated from the lateral lobules by the two sulci paramediani, one of which lies on either side of the vermis. The vermis itself is divided into four lobules, respectivt'ly indicated as C~2 and C-1, 4U» FORM AND I'^UNCTIONS OF THE CENTRAL NERVOUS SYSTEM j; and A. The fispura sci'imda passes ljct\v(-en C-1 and B. The lateral lobules aic divided into two main portions, lhe lobuhis ansifonnis and the form aiio veriidcularis. These lolmles are separated Ijy a deep incisure, the largest fis- suiv in the ceivljelluiu, the hssura parailoccula. The lobulus anciformis is divided l:iy a transverse hssure, the :-:nlcii:< tnlri-cruraUs, into Crus I and Crus II. Where the loluilus aiicil'omiis and 1 he foiinatio verinicularis come into relation with the |)oslei'ii)r ine(han iuliule, there is a poi'lion of the cerebellum which B(jlk dehnes as tlie lohiis piimiiirilicniis. Bolk exjilains the strikinR variations of the cerebellum on the grounds that form is de])endent upon function, and there must, tli<'i-efoie, Ije some direct functional rclalionship between these variations in the cerelxdlum and the contif.l of the muscular system whose tonic, sthenic and static activities ai'e dependent upon this ..'rgaii. He concludes that all of the muscles of the body may be divided into two groups: liaise wha'li act l)datei-al!y together, such as the trunk muscles, . 1 ra I'aranoc-culus Lobvilas Ans Florrularis liitili ruralis iiatio Vrrraicularis Lobus I^arainodiani]^ Fissuia Sc'-'i Fissura Paianifdi; C 2 C 1 B A Fic. -jOt. — Scliciaatizution ef tlio fundamental arrannoment of tlic parts of tlie mammalian cereljclluni sprcail out in one |)lani', according to Bolk, who selected for liis type the cerebellum of linnir nlhifron.^. and those which, allhoiigli bdaterally present, ha\a' a certain independence in their activity, like the muscles of the tirms and legs. The muscle groups which show this inrlepenclence cif action are unilaterally synergic, while those which depend uiion a simultaneous coordination are l)ilaterally synergic. To the latter group fielong the muscles whii'h prodtice movements of the head, of the eyes, of the mouth and jaws, of the tongue, pharynx and laiynx, and of the trunk, in addition to certain movements of the upper and lower extremities which i-etjuii-e Itilateral innerA'ation and act together as in locomo- tion. Upon tliis hypothesis Bolk bases his localization in the cerebellum of control for the two major group.s of muscles. The cerebellar cortex is com- posed in mammals of a number of coordinating centers, some of which are paired for unilateral synergic control, while some are unpaired for Ijilateral synergic I'ontrol. The loh'idns anterior cercbrUi contains the coordinating centers for the muscles whieli are active in mo\-{'menls of tlie ln'ad. The most anterior lobule is for the eyes; the seeond hilmle, for the tongue; the third, for the muscles of mastication, and the fourth, for the muscles of expi'ession and ot the larynx and pharynx, ^riie lohiihi.^ simplex contains the unpaired synergic THE CEREBELLUM 417 centers for the muscles of the neck. In the upper portion of the lobulus medianus posterior are the unpaired centers for movements of the left and right extremities. The lobuh ansiformes and paramediani contain paired centers for the extremities, the arrangement of the centers in each case being homolateral, Crus I corresponding to the arm of the same side and Crus II to the leg of the same side. The remainder of the cerebellum contains co- ordinating centers for the trunk and the tail region, the formatio vermicularip particularly having control of the tail. This localization in the cerebellum by Bolk on the grounds of compara- tive anatomy was subsequently confirmed by Andr^ Thomas and Durupt and by Van Rijnberk by experiments upon animals. Uniformity of the Internal Structure of the Cerebellum. Throughout the vertebrate series, the cerebellum presents a striking uniformity in its internal structure, and is so different from other parts of the central nervous Lobus Anterius; Caput Lobus fLobulua Posterior [ Anaiformis Lobus Paramedianus, Lobus (Lobulus ^ r'r.io tt Posterior \ Ansiformis \ ™ Formatio Vermieularis; Pars Tonsillaris Fissura Secunda Lobus Simplex Crus I Formatio Vermicularis ; Lobus Petrosus Formatio Vermicularis ; Flocculus Cauda C 1 ] I anus Posterior Lobus Medi- FiG. 305. — Schematization of the parts of the mammahan cerebellum spread out in one plane. (Van liijnherl:.) system as to suggest a definite specialization of function which has been present almost from the first in vertebrates. This uniformity in the internal structure appears in the arrangement of the nerve cells and the fibers participating in the formation of the cerebellum. The innermost layer of nerve cells consists of medium sized elements which are placed closely together and give the area a granular appearance. This is the granular layer. The dendrites of the cells of this layer extend toward the surface and spread out to form a second layer of about the same depth consisting mainly of end branches of axones, among which are scattered a few nerve cells. This is the molecular layer. On the border between the granular and molecular layers, there develops a row of large cellular elements placed in regular order along this boundary line, the tells of Purkinje. Running along this border-hne, in relation with the cells of Purkinje, is a thin stratum of nerve fibers, while internal to tlie granular layer is a stratum of fibers 27 418 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM mm '-"' ■ --. ■•' Fi(.i. 306. — Cortex cerelH-Ui in shark (Squahis acantli- ias), showing three strata of cells. sr* "{-^^.•»S>,. 7 /. Viii. 307. — Cortex cerebelli in turtle [Chdonia mijdes), showing three strata of cells. T " . t Fii:. :>( '»* / in fr ' . '^ > show ' >.• -•' cells. ^f * •-6- '. »•)' t . . IN. — Cortex cerebelli og [Uiuia sijhmtica), ing three strata of I Fig 309— Cortex c(rel)elh m alligator ( [llnjnl n Mi\- S(SSi/J/J(( HS/ I SJiOTling three strata of cells. 3' I- '.i'^"-^ ■ Fin. 310. — Cortex cerebelli m codfish {fladtis morrhua), showing three strata of cells. ^^sao^- THE CEREBELLUM 419 Fig. 311. — Cortex cerebelli m pigeon Fig. 312.— Corte.\ cerebelli in dog (Canis (Columba), showing three strata of familiaris), showing three strata of cells. cells. ■iV^^'Kasa. "' J T FiG. 313. — Corte.x cerebelli in raljbit Fic (Lepua), showing three strata of cells. 314.^Corte.x cerebelli in chimpanzee {Troglodytes niger), showing three strata of cells. 420 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM of somewhat greater thickness. These are known respectively as the ex- ternal and internal medullary strata. On the outer surface of the molecular layer is a thin stratum of nerve fibers called the marginal zone or zonal layer. In summary, the internal structure of the cerebellum presents: 1. The outermost zonal layer, made up of the end branches of axones from cells in the granular layer. 2. The molecular layer, containing the axones of the granular cells and the dendrites of the Purkinjc cells, among which are scattered afew nerve- cells. 3. The Purkinje layer, consisting of a single row of large Purkinje cells. 4. The external medullary stratum. 5. The granular layer, consisting mainly of granule cells. 6. The internal medullary stratum. This type of internal structure is seen inall vertebrates with the exception of the cyclostomes, in which the differentiation into layers, although indis- tinct, is far enough advanced to foreshadow the ultimate cerebellar strati- fication. In the lower vertebrates, a recess or series of recesses connected with the fourth ventricle extends into the cerebellar evagination. In mammals, the diverticula from the ventricle are not present, because this space is now occupied by a branching mass of white matter which constitutes the arbor vita. In addition to these histological elements which are constant in the verte- brate series, several other more diffuse masses of gray matter appear in relation with the medullary substance. (3ne of these bodies of gray matter consists of a bilateral collection of nerve cells, the nucleus globosus, one situ- ated upon either side in the vermis near its cephalic extremity. These two nuclei are well developed in mammals and in birds. Thej' are present, though less well defined, in reptiles and amphibia. There is some evidence of their presence in certain groups of fish. In birds and reptiles, there is a small collection of nerve cells lateral to the nucleus globosus, constituting the nucleus lateralis, which is prol.iably identical with a liighly developed nucleus in mammals, the nucleus denta.tus. In reptiles, birds and mammals, two distinct nuclei appear in the roof of the fourth ventricle mesial to the nucleus globosus. These are the nuclei Iccli or jastigii, while somewhat ventro-mesial to the nucleus dentatus in mammals is a large collection of nerve-cells, the nucleus emboliformis. CVjlleeti\'ely, these nuclei occupying positions in the white matter are spoken of as the medullary nuclei of the cerebellum. Even within the narrow limits of the primates, these medullary nuclei vary nuich in their distinctness and prominence. It is only in man, gorilla, chimpanzee, orang-outang and gibbon, that the nucleus dentatus has the typical convoluted appearance which reseml)les the inferior olive of the medulla, a fact which has led to the term, olira cerebelli. In the lower apes, the convoluted appearance of the cereliellar olive is scarcely discernible. Primitive Connections of the Cerebellum. The cerebellum receives root fibers from several somatic sensory ner\'es, notably the fifth, which, in the fish, establish a primary connecticm with lateral line organs of the THE CEREBELLUM 421 supra-orbital, infra-orbital and hyornandibular rows. In many of the fish there is also a large vagus connection. In all of the lower vertebrates, in- cluding birds, the cerebellum is connected with secondary somatic sensory tracts of the somesthetic, optic and auditory centers. There is a primary splanchnic sensory connection in the cerebellum serving the gustatory sense, and likewise a secondary pathway through the cerebellum for this type of sensibility. All of the more exact connections of the cerebellum among vertebrates are difficult to enumerate at the present time. The verte- brates, exclusive of birds and mammals, possess two tracts which connect the diencephalon with the cerebellum. These are particularly well developed in teleosts and selachians, although less well defined in amphibians and reptiles. They are the traciiis diencephalo-cerebellares. In fish, amphibia and reptiles, the brachium conjunctivum anterius contains three main tracts : 1. The tractus tegmento-cerebellaris, which arises in the ganglion at the caudal end of the tegmental portion of the diencephalon and is a crossed connection having its decussation in the cephalic extremity of the midbrain. 2. The tractus mesencephalo-cerebellans, which is also a crossed connection with its decussation in the superior medullary velum in close relation with the decussation of the trochlear nerve. 3. The tractus tecto-cerebellaris, which is likewise a crossed connection arising in the tectum of the mesencephalon and having its decussation in the velum forming part of the decussatio veli. In all vertebrates, the brachium posterius, known in mammals as the inferior cerebellar peduncle, contains fibers from the following sources : 1. Tractus spino-cerebellaris, both a direct and crossed connection. 2. Fibrce arcuatce anteriores and posteriores. 3. Tractus vestibulo-cerebellaris and, in selachians and teleosts, a tractus trigemino-vago-cerebellaris. In mammals, the posterior brachium is augmented by a large contingent from the inferior olive constituting the tractus olivo-cerebellaris. From these connections it is evident that the cerebellum, even from its earliest history, has borne an extensive relation to all the different forms of sensibihty, including somesthetic, optic, auditory and gustatory. It is also provided with an ample association system, which permits the organ to serve as a center for correlation. This sensory correlation has had, from the inception of cerebellar development, a definite purpose, as shown by the internal structure of the cerebellum, which has maintained a constant morphological character. The function of the organ must, therefore, have been constant, and its correlation of sensory impulses derived from so many different sources must have had a common aim. All of the facts seem to in- dicate that this correlation was in the interest of regulating motion by the addition to motor performance of that essential element termed synergic control. The Connections of the Cerebellum in Mammals. With the exception of the gustatory connection, which no longer plays a part in the sensory contributions entering into cerebellar correlation, the sensory tracts to the 422 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM cerebellum in mammals indicate that the essential nature of the organ has remained unchanged through the later stages of evolution. Three peduncles with certain accessoi-y connections serve to connect the mammalian cere- bellum with the rest of the central axis. These are the superior cerebellar peduncle, corresponding to the brachium conjunctivum anterius ; the m/en'or cerebellar peduncle or rvatijonn body, corresponding to the brachium pos- terius, and the middle cerebellar peduncle, a mammalian accjuisition not pre- sent in the lower vertebrates. According to the observations of Van X'!" 'V Fii;. 31.5. — Cortex cerebcUi in man, showing three strata of cells. Gehuehtcn, the following functional groups of fibers participate in the •cerebellar connections : 1. Through the inferior cerebellar peduncle, which contains: (a) The dorsal spino-ccrebellar tract from the muscles, joints and tendons. (6) A secondary connection with the columns of CJoll and Burdach through the anteiior and posterior arcuate fibers establishing direct and crossed connections, also from the muscles, joints and tendons; and possibly from the skin. ic) The olivo-cerebellar tract, direct and crossed, connecting both THE CEREBELLUM 423 inferior olives with the cerebelhim, coordinating the movements of the head with those of the eyes. 2. Through the juxtarestiform body, which contains: (a) A Deitero-cerebehar tract connecting the nucleus of Deiters with the nucleus tecti of the cerebellum for equilibratory control. (6) A secondary connection between the substantia gelatmosa, (rep- resenting the trigeminal nerve) and the vermis of the cerebellum. 3. Through the superior cerebellar peduncle, which contains the Lenticultir ~ f- Nucleus / Exte rnal Capsule Internal Capsule Vestibular Nerve Cochlear Nerve Ventral Cochlear Nui 1) u- Tuberculum Ac()U-.licuii ^vfp. ^ Y-i Fig. 310. — Course of some of the greater conduction paths in the brain. {Held.) On the left side the cerebellum has been completely removed, as has the cerebrum, with the exception of the large ganglia; on the right side the posterior superior part of the cerebral hemisphere has been removed by a vertical (not e.xactly frontal) and a horizontal section. The brain is viewed from the left and from behind. {Spalteholz.) dentato-mesencephalic and the dentato-diencephalic fibers, the former ending in the red nucleus after a complete decussation in the mid- brain, and the latter extending to nuclei of the thalamus. It is possible that some fibers extend from the red nucleus to the dentate nucleus; but the superior cerebellar peduncle serves as the chief pathway for impulses leaving the cerebellum. 4. Through the middle cerebellar peduncle, which contains fibers serving as a connection between the frontal, occipital, parietal and temporal lobes of the cerebral hemispheres and the lateral lobes of the cerebellum. This establishes a completely crossed connection through the pontile decussation. 424 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM 5. Through the fibers of the ventral spino-cerebellar tract, which enter the vermis of the cerebellum after traversing the lateral aspect of the superior cerebellar peduncle. It is evident that the cerebellar connections in mammals indicate the same functional capacity as in the lower vertebrates. The fibers in the in- ferior cerebellar peduncle re- present an extensive connec- tion between the muscles, bones and joints and, per- haps, to some degree the cutaneous surfaces of the body. The juxtarestiform body is indicative of a con- nection between the semi- circular canals, utricle and saccule of the internal ear on the one hand and the cere- bellum on the other, still re- taining the ancient relation which in many of the lower vertebrates is much more extensive, because it includes the organs of the lateral line. The connections through the middle cerebellar peduncle provide opportunity for more efficient sensory associations than in the primitive forms, since they mediate sensory impulses arising in the oc- cipital, temporal, parietal and frontal lobes of the cere- bral hemispheres, and serve respectively for the ultimate elaboration of visual, audi- tor}', somesthetic and kines- thetic impressions. The superior cerebellar peduncles represent ampli- fied pathways by means of which fibers leave the cere- bellum for the spinal cord and brain-stem. This is a more voluminous con- nection, because the correlation which occurs in the cerebellum of mammals, being more extensive and complex, needs a larger pathway for tlistribution. The Evolutional Significance of the Cerebellum. From the early stages of vertebrate history, the cerebellum has served as an organ of association O'P Fig. 317. — Diagram of the afferent and efferent tracts of the cerebellum. The arrows indicate the directions of the impulse. {Cajat.) A, B — Vostibulnr ci.Ils whose nxoncs prohably send tln'ir asoendinp bifurcatin/j; brunches to join with the Purkinjo cells. C — Fibers of the vestibular nerve. CB — Crossed cerebeUo- bulbar tract. Ct — Decussation of the superior cerebellar ped- uncle. D — Ascending branch of the vestibular axone, probably joining with tlie Purkinje cells. E — Dentate nucleus giving rise to the superior cerebellar peduncle. F — Ganglion of the roof, at the point where the crossed cerebeljo-bulbar tract commences. G — Nucleus giobosus and emboliforniie. H — .Superior cerebellar peduncle. / — Direct descending branch of superior cerebellar peduncle. J — Crossed descending branch of the peduncle. A' — Ascending sensory tract originating in Clarke's column and probably joining with the granule cells by the intermediation of the mossy fibers, hf — Spinal ganglion. .V — Termination of the crossed cfescending branch of the superior cerellellar peduncle in the anterior horn cell of the cord. O — Muscle tendon organ of KQhne. /■* — Posterior root partly joined in Clarke's eolunin. Q — Anterior or motor root. R — Spino-cerebellar sensory tract. S — Purkinje cell. T — Mossy fibers. V — Clarke's column giving rise to the ascending cerebellar sensory tracts THE CEREBELLUM 425 for sensory impulses which are correlated and distributed in order to maintain the muscles of the body in a state of synergy. The advantages accruing to this process from the combination of vestibular, auditory, somesthetic and optic impressions cannot be called in question. The most primitive vertebrate motion depends upon the harmonious in- nervation of the axial musculature, whose action must be coordinated from body-segment to body-seg- ment, and synchronized upon the two sides of the body. Such animals as depend upon swimming move- ments for their locomotion, and in which swimming movements repre- sent the maximum motor achieve- ment, require a bilateral synergic control. The mechanism best calcu- lated to supply this control would consist of unpaired interdependent collections of coordinating cells. Such an organ is the cerebellum in all of the fish. In some lower verte- brates the necessity for this bilateral synergic control is much less than in others, as for example the cyclostomes, which are animals solely dependent upon a vermicular Fig. 31S. — Diagram of the superior and movement for all their motor ac- inferior motor tracts of the cerebellum, tivity. A similar vermicular move- (Cajal.) , , . „ ^ . *^ A — Motor zone of the bram. B — Cortico-ponto- ment is sufficient in the reptiles to cerebellar tract. C— Cortioo-splnal tract fl— Pontile nuclei. E — Ponto-cerebellar tract or middle cerebellar carry them over the surface of the peduncle. F— Purkinje axoncs. G— Dentate nucleus. ^ H — Bifurcation of the superior cerebellar peduncle. ground. This is also true of the J— .Ascending tract of Marchi. /^Descending " 1 .1 • dentato-spinal tract. L — Crossed pyramidal tract. more sluggish of the amphibia M— Anterior root of the cord. A'— Red nucleus. ^ . . N' — Oculo-motor ner-\'e. whose movements are of a similar character. Even the more active amphibians, such as the frog, are funda- mentally dependent upon vermicular movement. In their larval state, locomotion resembles that of other swimming animals. The extremities when acquired have no great independence one from the other but are regulated in such a way as to cooperate almost as a single organ. In the same manner the movement of the birds, both tnose depending upon the wing and the running birds, require bilateral synergic control. This is especially true in flight, where the innervation of the wings must be subjected to the most exact sort of bilateral control. In the mammal, a new phase of motion is developed with the appearance of extremities, each of which has actual independence of action. An increasing degree of such independ- ence determined the semibiped condition, and finally released the upper extremities from responsibility in locomotion. But even before this inde- 426 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM pendence of the arms was achieved in the biped, many of the quadrupeds gained the ability to control one foreleg independently of the other, and had a similar independence in the hind extremities. It was largel}' in con- sequence of these unilaterally synergic activities that the hemispheres of the cerebellum made their aiijiearance. This fact becomes significant in the light of Bolk's investigations, which go to show that in all mammals the lobulus ansiforniis in its two divisions, the anterior and posterior crura, is present, and furthermore that these parts become increasingly more complex with the increased complexity in the independent movements of each limb. In summarizing the evolutional significance of the cerebellum, it ma}^ be concluded : 1. That the cerebellum has Ijcen added to the neuraxis as a supraseg- mental structure in the interest of coordmation. 2. That in its primitive form it correlates sensory impulses received from all of the chief rec<'ptors of the body, and utilizes the impulses thus associated most advantageously to accomplish the purposes of coordination. 3. That in the lower vertebrates this coordination requires the harmoni- ous action i)f the axial musculature, and depends upon the bilaterally synergic control (jf the central arched portion of the cerebellum, correspond- ing in position to the vermis, although certain lateral structures, such as the paraflocculus and flocculus, were added for the more or less independent movements of the tail. 4. That when the upper and lower extremities made their appearance and became capable of independent movements, they needed something more than bilaterally sj-nergic control. Out of this necessity grew the ex- pansive lateral portions of the cerebellum, the cerebellar hemispheres, which provide unilateral synergic contrnl for the arms and legs, exercising regu- lation over such independent and individual movements as these extremi- ties have the capacity to develo]). .5. That, as a natural (■(;)risefiuence, the greater the range of independent movement in the extremities, the greater has become the cerebellar area required for its c(.)ntrol. 6. Tlrat the greatest range of independent movement is seen in the skilled performances which are the special attributes of man, who, as a result, has the most highly developed cerebellar hemispheres. 7. That the central or vermal portion of the cerebellum not only still retains its primitive control of the bilaterally synt-rgic movements of the eyes, face, tongue, jaws, larynx, n(>ck and trunk, Ijut also maintains a similar relation to movements of the extremities which rec]uire bilaterally SA'nergic control. CHAPTER XXIV THE CEREBELLUM RELATIONS, SURFACE APPEARANCE AND ANATOMY General Relations and Boundaries. The cerebellum is situated in the posterior fossa of the skull. It lies beneath the tentorium and caudal to the posterior surface of the petrosal portion of the temporal bone. In the base of the cranium it occupies all except that mesial portion of the posterior fossa which affords support to the pons and the medulla oblongata. Al- I*arictal Bone Frontal Bono Lobus Frontalis Frontal Sinu^ Sphenoid Pituitarj- Gland Pons \"arolii Basi-Ofcipital Bone Medulla Oblongata Lobus Parietalis Corpus Callosum ra Mater Lobus Occipitalis Tentorium Cerebellum I Vermis) Occipital Bone Fig. 319. — Sagittal section of brain in situ. though distinguished from the segmented portion of the brain-stem by its general character, it has no well defined boundaries. A boundary hne may be drawn, however, at the junction of either middle cerebellar peduncle with the cerebellum. This junction is referred to as the kilus ccrebelli. Surface Relations. The cerebellum by its dorsal or tentorial surface is m contact with the tentorium ccrebelli, which separates it from the occipital lobe of the cerebral hemispheres. The straight sinus ma.kes its way m the dura mater at the junction of the tentorium and falx cerel:)ri in the midline above the cerebellum. The ventral or occipital surjace rests upon the dura covering the two 427 428 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM cerebellar fosste of the occipital bone; in the midline it is in relation with the occipital smus and the cisierna magna. The cephalic or petroso-ventricular surjace lies in contact with the dura mater covering the posterior surface of the petrosa, and with the roof of the fourth ventricle. The most lateral aspect of this surface is in close relation with the sigmoid and bulbar portions of the lateral sinus. It is separated from the 7nastoid cells of the temporal bone by the thin inner osseous cortex and the dura attached to the bone. This relation has especial importance in con- nection with suppurative processes in the mastoid cells which may, upon occasion, erode the bone and thus gain access to the cerebellum. This surface is also in intimate relation with the internal auditory meatus which transmits the seventh and eighth nerves. Mesial to the meatus is the jugular foramen for the transmission of the lateral sinus, the vagus and the glossopharyngeus nerves. The junction of the dorsal and ventral surfaces is indicated by a rounded border which, extending from the midline, is successively in rela- tion with the torcular Herophili and the lateral sinus. At the junction of the ventral and cephalic surfaces, the lateral sinus turns downward to form the sigmoid and bulbar portions of this venous channel. Dimensions, Weight and Coverings. The greatest transverse diameter of the cerebellum is 10 cm. Its greatest cephalo-caudal diameter is 5 cm. Its greatest ventro-dorsal diameter is 5 cm. It weighs 140 gm., or about one- tenth of the entire brain weight. By its ventral surface, the cerebellum is in close relation with the occipital bone. The cephalic surface is in relation with the petrosal portion of the temporal bone. The dorsal surface of the cerebellum in man is in contact throughout its entire extent with the tentorium cerebelli. In certain mam- mals, this membranous plate is replaced by a bony structure forming an osseous tentorium. In some instances, partial ossification of the tentorium has been observed in man. The dura mater forms a complete investment about the cerebellum. In the posterior fossa it forms the endosteum of the occipital bone and petrosa of the temporal bone. The dural investment of the cerebellum is completed by the tentorium, which is stretched across its dorsal surface. Several special processes of the dura mater are in relation with the cerebellum. One of these, the./o/:r cerebelli, is attached to the under surface of the tentorium in the midline and also to the internal occipital crest. It extends toward the foramen magnum, where it bifurcates into two pro- cesses, each of which gradually fades out along its respective margin of the foramen. The falx cerebelli is inserted between the two halves of the cere- bellum in the po.stcrior cerebellar notch. Its attachment to the bone in the occipital region forms the occipilcd sinus. Another specialized process of the dura is the lateral sinus, which is situated at the attachment of the tentorium to the occipital and temporal bones. In and near the midhne this sinus becomes dilated to form the torcular Herophili. Laterally it extends in both directions toward the groove of the sigmoid portion oj the lateral sinus, where it turns directly downward THE CEREBELLUM 429 to approach and enter the jugular foramen. The tentorium is attached to the superior border of the petrosal portion of the temporal bone, and in this line of attachment forms the superior petrosal sinus. The arachnoid affords its usual covering situated between the pia and the dura, forming a large subarachnoid space, which spreads about the dorsal aspect of the medulla and along the ventral as well as the dorsal surface of the cerebellum immediately adjacent to the midline. This exten- sion of the subarachnoid space is part of the cisterna magna. The subarach- noid space in connection with the cerebellum elsewhere is not so ample, and makes provision only for a thin layer of cerebrospinal fluid. The pia mater is a close vascular investment of the cerebellum, as it is of other parts of the nervous system. It contains the arteries and branches of the arteries which supply this organ. The membrane dips into all of the larger cerebellar fissures as well as into the primary and secondary sulci. In order to disclose the actual surface of the cerebellum, this membrane must be stripped off. Arteries of the Cerebellum. The cerebellum receives its arterial supply from the superior cerebellar and the anterior inferior cerebellar arteries, both branches of the basilar artery. It is also supplied by the posterior inferior cerebellar arteries, branches of the vertebral arteries. Parts of the Cerebellum. The cerebellum consists of three parts: A central portion or vermis, and two lateral lobes or hemispheres. In man, a still further subdivision is estabhshed by following the course of the great horizontal fissiire which divides both the vermis and the hemi- spheres into an upper and lower portion. The part lying above the horizontal fissure is the superior portion of the cerebellum, and that lying below is the inferior portion. After removal from the skull and detachment from the rest of the brain- stem, the cerebellum has much the appearance of a butterfly with wings outspread. The body of the butterfly is the vermal portion, while the wings correspond to the hemispheres. The great horizontal fissure is located by noting the position and relations of two prominent triangular areas which appear on the petroso- ventricular surface, into which the middle cerebellar peduncles enter. The apex of each triangular space is directed outward, and from this point the great horizontal fissure begins. It passes around the entire circum- ference of the cerebellum, dividing it into its superior and inferior portions. Sometimes, however, it is interrupted on the vermis, being deep enough only to make an incisure upon the more lateral aspect of the central portion. It is visible on the dorsal surface of the cerebellum for a short distance as it approaches the posterior notch, while in the remainder of its course it tra- verses the ventral and cephalic surfaces. Although important as a landmark in the description of the human cerebellum, the sulcus horizontalis cere- belli is, from the morphological standpoint, of secondary importance. It appear.s as a fissure developed late m man, and in many mammals is alto- gether wanting. 430 FORM AND FUNCTIONS OP THE CENTRAL NERVOUS SYSTEM Fig. 320. — The tentorial surface of the cerebellum. Fm. 321. — The occipital surface of the cerebellum. Fig. 322. — Tlie petrcjso-ventricular surface of the cerebellum. THE CEREBELLUM 431 Surface Appearance of the Cerebellum. After removal of the pia mater, the cerebellum presents a characteristic appearance which identifies it in all mammals and in most of the lower vertebrates. It consists of a series of fissures and sulci which run more or less regularly in parallel hnes trans- versely across the surface. These parallel fissures are fairly close together, so that they give the surface of the organ the appearance of a series of suc- cessive narrow strips, each strip being comprised between two fissures. The area between two of these transverse sulci constitutes ajolium. In some cases the sulci descend to a considerable depth; in other instances they are shallow. In the human cerebellum, the transverse fissures and folia extend completely across the surface. As a consequence, each fohum has a vcrmal portion and two hemispheral representatives, one extending to the right Lobulus Centralit Anterior Cerebellar Notch Sulcus Postceatralis Sxilcua Preclivalis Ala Lobuli Centralis Culmen Clivus Lobulus Lunatus Anterior Lobulus Lunatus Posterior Lobulus Postero- Superior Lobulus Postero-Inferior Sulcus Postclivalis Lobulus Postero-Superior Sulcus Tlorizontalis Posterior Cerebellar Notch Fig. 323. — Tentorial surface of the human cerebellum showing fissures and lobes. and one to the left. The deeper fissures constitute the lines of division which make possible the identification of certain lobes and lobules. From the ana- tomical as well as from the histological point of view, the jolium is the cere- bellar unit o/ structure. Surfaces of the Cerebellum. The surfaces of the cerebellum have been described in several ways; but for practical purposes, three surfaces may be distinguished : 1. The tentorial surjace, which occupies a dorsal position and takes significance from its relation with the tentorium ccrebelli. 2. The occipital surjace, which occupies a ventral position and is in re- lation with the occipital foss£e. 3. The 'petroso-ventricular surjace, which occupies a cephahc position and 432 FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM is in relation with the petrosal portion of the temporal bone and the roof of the fourth ventricle. This designation of the surfaces is of value from the surgical standpoint, inasmuch as it gives the leading anatomical character of each surface which may be readily visualized and made use of in operative procedure. The tentorial surface lies immediately beneath the tentorium and takes its general contour from this structure. It presents a central ridge-like elevation which extends from the cephalic to the caudal extremity of its surface. Its cephaUc extremity comes into relation with a small incisure, the anterior cerebellar notch (incisura ccrebclli anterior) . Its caudal extremity terminates in a much larger incisure, the posterior cerebellar notch (incisura cerebelli posterior). The central ridge of the tentorial surface represents the superior TonsiUa Anterior Cerebellar Notch Cerebelli Mediua ^;^,^^[^ ] [ If I.obulus Postero-Inferior P\'ran]i3 I Lobulus Biventralis ^■alIecula Tonsilla Fig. 324. — Occipital surface of liuman ceretiellum showing fissures and lobes. vermis which, with the exception of a very small portion, is situated entirely in this region. A smaller portion of the superior vermis, however, is lod;;ed in the anterior cerebellar mAvh an<:l brought to view upon investigation of this incisure. In the midline the ridge lies beneath the straight sinus. In a lateral po,sition are the greatly expanded cerebellar hemispheres. Each folium of the vermis extends to the right and k'ft upon this surface of the cerebellar hemispheres. In general contour the tentorial surface is concavo-convex and starting at the ridge of the vermis, the surface slopes away obliquely toward the lateral extremity of the hemispheres. The dural relation of this surface is important in surgical explorations of the posterior fossa, for if the tentorium be incised it is lik(