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 Anatomy and physiology of the nervous sy 
 
 latomy and physiology o 
 
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 3 1924 031 294 089 
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Cornell University 
 Library 
 
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 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/cu31924031294089 
 
ANATOMY AND PHYSIOLOGY 
 
 OF THE 
 
 NERVOUS SYSTEM 
 
 BY 
 
 SEDGWICK MATHER, M. A., 
 
 PROFESSOR OF NEUROLOGY, THE AUEBICAH COLLEGE OP NEUROPATHY 
 
 JOHN JOSEPH McVEY 
 PHILADELPHIA 
 
 1909 
 
Copyright, 1909 
 JOHN JOSEPH McVEY 
 
PREFACE. 
 
 The preparation of this work has been undertaken in re- 
 sponse to what experience in the class-room has shown to be 
 the need of a text-book especially adapted to beginners — a 
 book giving, by itself, a concise, but complete, presentation 
 of the physiology of the nervous system, together with the 
 more important features of its anatomy. In dealing with the 
 physiological phase of the subject, it has seemed best, viewed 
 from the student's standpoint, to confine the statements 
 mostly to the established and generally recognized facts, leav- 
 ing the numerous theories — fully and admirably discussed in 
 many contemporary works — to be taken up at a later stage 
 of the study, after the facts have been acquired and mastered, 
 this plan, it is found, being the most effective as a time- 
 saver, and resulting in the clearest and most lasting impres- 
 sions. The anatomical matter included in the volume is 
 only that which seems most necessary for an intelligent 
 understanding of the physiology, and of the most frequent 
 service in clinical work, the general text-book on anatoniy 
 always being available for further details. Both the struc- 
 ture and the various functions of the sympathetic system 
 have been set forth'with a fullness commensurate with their 
 importance. Of the whole work condensation has been the 
 guiding principle. 
 
 S. M. 
 
 Phixadelphia, Pa., Sept. 10, 1909. 
 
 (3) 
 
CONTENTS. 
 
 PAGE 
 
 PART I. 
 
 GENEEAL STRUCTDEE OF THE NEEVOUS SYSTEM AND 
 THE PHYSIOLOGY AND PEOPEETIES OF NEEVES 13 
 
 PART II. 
 
 STEUCTUEE AND FUNCTIONS OF THE CENTEAL 
 
 NEEVOUS SYSTEM. 
 
 Chapter I. 
 The Cerebrum , 25 
 
 Chapter H. 
 The Isthmus Cerebri 41 
 
 Chapter III. 
 The Pons 44 
 
 Chapter IV. 
 The Cerebellum 46 
 
 Chapter V. 
 
 The Oblongata 50 
 
 Chapter VI. 
 Connections Formed by the Afferent Cranial Nerves and the Afferent 
 Eoots of the Mixed Nerves, after Beaching the Central Nervous 
 System 55 
 
 Chapter VII. 
 
 The Spinal Cord 59 
 
 (5) 
 
6 CONTENTS. 
 
 PAGE 
 
 PART III. 
 
 INNERVATION OF THE SKELETAL PAETS OF THE BODY. 
 
 Chapter I. 
 General Distribution of the Spinal Nerves 'J- 
 
 Chapteb II. 
 General Functions of the Cranial Nerves 73 
 
 Chapteb III. 
 Innervation of the Eye <" 
 
 Chapter IV. 
 Innervation of the Nassal Fossae 79 
 
 Chapter V. 
 Innervation of the External Parts of the Head 81 
 
 Chapter VI. 
 Innervation of the Mouth 85 
 
 Chapter VII. 
 Innervation of the Internal Parts of the Ear 88 
 
 Chapter VIII. 
 Innervation of the Soft Palate and Tonsils and the Pharynx and 
 Larynx ^ 90 
 
 Chapter IX. 
 Innervation of the Cervical Region 94 
 
 Chapter X. 
 Innervation of the Shoulder and Arm 96 
 
 Chapter XI. 
 Innervation of the Hip and Leg , 102 
 
 Chapter XH. 
 Innervation of the External Genital Organs and the Perineum 107 
 
 Chapter XIII. 
 Innervation of the Respiratory Mechanisms 109 
 
COMMM-&. 7 
 
 PAGE 
 
 PART IV. 
 
 THE SYMPATHETIC NEEVES AND THE INNEKVATION 
 OF THE BLOOD-VESSELS AND VISCERA. 
 
 Chapter I. 
 Formation and Relations of the Sympathetic System 117 
 
 Chapter II. 
 Innervation of the Blood-vessels 128 
 
 Chapter III. 
 Functions and Properties of the Vaso-motor Nerves 134 
 
 Chapter IV. 
 Innervation of the Visceral Organs and the Physiological Action of 
 the Visceral Nerves 138 
 
 Index 147 
 
LIST OF ILLUSTRATIONS. 
 
 PLATE PAGE 
 
 1. The Cerebrum Viewed from Above 25 
 
 2. Diagrammatic Kepresentations of the Fissures and Convolutions 
 
 of the Outer and Mesial Surfaces of the Cerebrum 30 
 
 3. The Brain as Seen from Below and in Front 34 
 
 4. Diagrammatic Kepresentations of the Outer Surface of the Left 
 
 Cerebral Hemisphere 37 
 
 5. The Floor of the Fourth Ventricle and Neighboring Structures. 54 
 
 6. The Bight Side of the Spinal Cord with the Spinal Nerves 
 
 Attached 59 
 
 7. Cross Section of the Spinal Cord 62 
 
 8. Nerves of the Eye and the Upper Part of the Mouth 76 
 
 9. Mandibular Division of the Trifacial Nerve 82 
 
 10. Deep Nerves of the Upper Cervical Eegion 92 
 
 11. The Cervical Plexus 94 
 
 12. The Brachial Plexus and its Principal Lateral Branches 96 
 
 13. Nerves of the Front of the Forearm 100 
 
 14. Nerves of the Back of the Thigh 102 
 
 15. Deep Nerves of the Back of the Leg 104 
 
 16. The Eight Sympathetic Trunk 120 
 
 (9) 
 
PART I. 
 
 GENERAL STRUCTURE OF THE NERVOUS SYS- 
 TEM AND THE PHYSIOLOGY AND 
 PROPERTIES OF NERVES. 
 
ANATOMY AND PHYSIOLOOY OF THE 
 NERVOUS SYSTEM. 
 
 PART I, 
 
 GENERAL STRUCTURE OF THE NERVOUS SYSTEM AND 
 THE PHYSIOLOGY AND PROPERTIES OF NERVES. 
 
 The nervous system consists of a central 'part, which com- 
 prises the brain and spinal cord, and & peripheral part, which 
 comprises twelve cranial nerves, thirty-one spinal nerves and 
 the sympathetic system, the cranial and spinal nerves being 
 arranged in pairs. 
 
 The tissue of the nervous system, as a whole, falls into two 
 general classes, nerve-cells and nerve-fibers. Nerve-cells are 
 found in the brain and spinal cord and in outlying ganglia. 
 Nerve-fibers are present in all parts of the nervous system. 
 
 The nerve- tissue of the brain and spinal cord is divisible into 
 two kinds, distinguishable by their color. These are the gray 
 matter and the white matter. The gray matter is characterized 
 by the presence of nerve-cells. The white matter consists of 
 nerve-fibers. In addition to the nerve-tissue, the brain and 
 spinal cord contain a special type of connective-tissue, termed 
 neuroglia, which serves as support for the nerve-tissue. 
 
 The cell of nerve-tissue is known as the neuron. . 
 
 Ganglia. 
 
 A group of nerve-cells situated outside the substance of the 
 brain or spinal cord, is surrounded by a fibrous sheath, and 
 known as a ganglion. From the functional standpoint a 
 ganglion may be either sensory or sympathetic. Sensory gang- 
 lia are found on the posterior or afferent roots of the spinal 
 nerves, on the trunks of the fifth, seventh, ninth and tenth 
 
 (13) 
 
14 GENERAL STRUCTURE OF THE NERVOUS SYSTEM. 
 
 cranial nerves, and at the peripheral end of the auditory- 
 nerve. Sympathetic ganglia are situated along the course of 
 the nerves and in the tissues of many of the visceral organs. 
 In size ganglia vary, the smallest being of microscopic 
 dimensions and the largest an inch or more in length. 
 
 Structure of the Neuron. 
 
 The neuron is the anatomical unit of the nervous system. 
 It consists of a central part, or nerve-ceU, with more or less 
 elongated outgrowths of its substance called processes. The 
 processes are of two kinds, axis-cylinder processes or axons, and 
 dendritic processes or dendrites. The so-called typical neuron 
 has a single axis-cylinder process, which is often of consider- 
 able length, and several dendritic processes, which are always 
 branching and microscopically short. There are, however, 
 many neurons with but two processes, both of which are of 
 the axis-cylinder type. Running through the processes, as 
 well as the nerve-cell, are minute threads of nerve-tissue, 
 termed neurofibrils, which constitute the conducting part of 
 the neuron. 
 
 The nerve-cell contains a nucleus, and very often a nucleo- 
 lus. The nerve-cell and the dendrites also contain many 
 small particles of matter known as chromophile material, or, 
 more commonly, as NisVs granules. This substance is be- 
 lieved to serve as nutrition for the neuron. In lesions of the 
 neuron involving a loss of function, the chromophile material 
 breaks up into finer particles, and sometimes dissolves- and 
 disappears, the process being known as chromatolysis. 
 
 The axis-cylinder process is always surrounded by either one 
 or two sheaths. These are the medullary or myelin sheath, and 
 the primitive sheath or neurilemm.a. The medullary sheath is 
 of a color approaching white, and is composed of a soft, fatty 
 substance called myelin. This sheath is formed in segments, 
 which are practically uniform and a millimeter or less in 
 length. The intervals between the segments, where the 
 
NEBVE-FIBERS. 15 
 
 myelin is interrupted, are known as the nodes of Ranvier, and 
 the segments are known as internodes. The neurilemma is a 
 thin, net-like membrane, of an elastic nature and a somewhat 
 firm consistency. This sheath forms a continuous covering. 
 On its inner surface are nuclei, corresponding in number 
 to the segments of the myelin sheath (where the myelin 
 sheath is present), and in position to the nodes of Ranvier. 
 
 Nerve-fibers. 
 
 An axis-cylinder process with one or both of the sheaths 
 described above constitutes a nerve-fiber. An axis-cylinder 
 process with either a myelin sheath alone, or with a myelin 
 sheath and a neurilemma, constitutes a medullated or white 
 fiber. An axis-cylinder process with only the neurilemmal 
 sheath, constitutes a non-medullated or gray fiber. Nerve- 
 fibers vary in length from a small fraction of an inch to three 
 feet or more, and in diameter from two-millionths to tweiity- 
 millionths of a meter, the largest fibers being found in the 
 spinal nerves, and the smallest in the sympathetic system. 
 
 All fibers in the olfactory nerve, and the greater part of 
 those in the sympathetic system, have only the neurilemmal 
 sheath. All fibers in the optic and auditory nerves and in 
 the gray and the white matter of the brain and spinal cord 
 have only the medullary sheath. But in all the spinal 
 nerves and in all the cranial nerves,, except the olfactory, 
 optic and auditory, both sheaths are almost invariably pre- 
 sent. In some cases both sheaths are also found in the 
 sympathetic system. 
 
 Classification of Nerve-cells According to 
 their Processes. 
 
 Nerve-cells are classified as bipolar or multipolar, accord- 
 ing to whether their processes consist of two axis-cylinders, 
 or of one axis-cylinder and dendrites. 
 
 The bipolar cells form the ganglia of the posterior roots of 
 
16 GENERAL STRUCTURE OF THE NERVOUS SYSTEM. 
 
 the spinal nerves and the ganglia of the trifacial, facial, audi- 
 tory, glosso-pharyngeal and pneumogastric nerves. The two 
 processes of a bipolar cell coalesce and leave the cell as an 
 apparently single process, but they soon separate and run in 
 opposite directions, one entering the central nervous system, 
 and the other running outward in a peripheral nerve. Prom 
 the functional standpoint the bipolar cells are sensory cells, 
 and they furnish all the sensory fibers of the nervous system, 
 except those of the olfactory and optic nerves. 
 
 The multipolar cells are of two kinds, Golgi cells of the first 
 type and Golgi cells of the second type, distinguished by the 
 behavior of their axons. 
 
 The cells of the first type are characterized' by an axon that 
 leaves the gray matter in which it arises and forms a single 
 nerve-fiber. These cells are the source of all the fibers in the 
 white matter of the brain and spinal cord, of the efferent 
 fibers in the cranial and spinal nerves and of the fibers in the 
 sympathetic system. The cells of the second type are character- 
 ized by an axon that divides into several branches, the course 
 of which is confined to the gray matter in which they arise. 
 These cells are found only in the central nervous system, and 
 principally in the cortex of the cerebrum. The branches of 
 the axons all terminate in contact with other neurons, so that 
 the impulses received by these cells are often widely dis- 
 tributed. They are frequently described as ' ' association 
 nerve-cells," in consequence of their role in the higher 
 activities of the brain. 
 
 Structure of Nerves. 
 
 The fibers that enter a peripheral nerve are grouped in 
 bundles or funiculi and held together by connective-tissue. 
 The tissue which surrounds each funiculus is called the peri- 
 neurium, that which extends among the fibers of the funiculus 
 is called the endoneurium, and that which envelops the whole 
 nerve is the epineurium. The perineurium and the endoneur- 
 
P17N0TWNAL CLASS! b'lOATtON OF NERVB-FIBEBS. 17 
 
 ium are continuous with each other. The epineurium con- 
 tains the lymph channels and the larger blood-vessels, and is 
 supplied with sensory nerves termed nervi nervorum. The 
 branches of the blood-vessels wind among the funiculi, and 
 the capillaries enter the funiculi and wind among the fibers. 
 When a funiculus divides, the perineurium is continued over 
 the new bundles, but grows thinner with each successive 
 division. Around each of the terminal divisions it forms a 
 thin envelope known as the sheath of Henle. 
 
 Functional Classification of the Fibers of the 
 Peripheral Nerves. 
 
 The activities of nerve-fibers are carried on under the in- 
 fluences of external agencies or stimuli. When a nerve-fiber 
 is acted upon by an external agency, that is, when it is stim- 
 ulated, a movement is started at the point affected by the 
 stimulus and the movement is propagated along the fiber. 
 This movement, whatever it may be, is called an impulse, and 
 its propagation along the fiber is termed conduction. 
 
 A nerve-fiber normally conducts in only one direction. In 
 the fibers of the peripheral nerves conduction is either from 
 the central nervous system to other parts of the body, or 
 from other parts of the body to the central nervous system. 
 The peripheral fibers, therefore, are of two general classes : 
 efferent jibers, whose conduction is outward or centrifugal ; 
 and afferent fibers, whose conduction is inward or centripetal. 
 
 The efferent fibers consist of the following groups : 
 
 (1) Motor Fibers. — These are distributed to muscles, 
 both voluntary and involuntary, and the effect of their activity 
 is muscular contraction. The motor fibers of the involuntary 
 muscles are divided into three sub-classes : the viscero-moior 
 fibers, which supply the visceral organs ; the pilo-motor fibers, 
 which supply the erector muscles of the hair, and the vaso- 
 constrictor fibers, which supply the arteries. 
 
 (2) Inhibitory Fibers. — These are distributed to the 
 2 
 
18 GENERAL STBVCTUBE OF THE NERVOUS SYSTEM. 
 
 visceral organs, where they are known as viscero-inhibitory 
 fibers, and to the arteries, where they are known as vaso-dila- 
 tor fibers. The activity of this class, of fibers is manifested 
 only in muscles in a state of contraction, and in these it pro- 
 duces a lessening of contraction or relaxation. 
 
 Note. — The efferent fibers of the arteries are known collec- 
 tively as vaso-motor fibers. 
 
 (3) Secretory Fibers. — These fibers have been physiol- 
 ogically demonstrated in connection with some of the glands, 
 particularly the salivary and gastric glands and the pancreas 
 and sweat glands. The secretory fibers of the sweat glands 
 are derived from the spinal cord and reach the glands by way 
 of the cutaneous nerves^ but those to all other glands reach 
 their_destinati«n in the nerves that supply the vaso-dilator 
 fibers. 
 
 (4) Trophic Fibers — The normal nutrition of all tissues 
 is dependent upon their connection with normally acting 
 nerves. But trophic nerve-fibers, or fibers whose exclusive 
 function is the regulation of nutrition, have not as yet been 
 anatomically separated, nor is there conclusive physiological 
 evidence that such fibers form a distinct class. Nutrition is 
 in intimate association with blood-supply. In disorders of 
 nutrition accompanied by hypertrophies it is commonly ob- 
 served that the blood-supply is increased, and in atrophies 
 that the blood-supply is diminished. From these and other 
 similar observations it is evident that the fibers controlling 
 nutrition, even if they have an independent existence, are at 
 least in close functional relation with the vaso-motor nerves. 
 Until fibers of a strictly trophic function have been discov- 
 ered, it may be assumed that the vaso-motor fibers are the 
 main nervous factors in nutritional control. 
 
 The afferent fibers are distributed to all classes of peripheral 
 tissues and to the cerebral and spinal meninges. These fibers 
 are so connected at the nerve-centers that the final effect of 
 their impulses is manifested both as reflex action in the peri- 
 
IRRITABILITY, CONDUCTIVITY AND STIMULI 19 
 
 phery and as sensation in the brain. They are commonly 
 known as "sensory nerves," and, in most cases, they each 
 mediate a distinct and characteristic kind of sensation. They 
 are classified with the different sense-organs, of which they 
 form the conducting parts. 
 
 Irritability and Conductivity. 
 
 The term irritability signifies the property or attribute in 
 consequence of which living animal tissue may be made to 
 manifest or modify its regular functional activities under the 
 infiuences of external agences or stimuli. The term conduc- 
 tivity is used to designate the power which tissue possesses 
 of conducting through its substance the effects produced upon 
 it by an external agency acting at a given point. These 
 properties are common, in some degree, to all tissues, but 
 attain their highest development in the tissues of the nervous 
 system, where they constitute indispensable conditions of 
 activity. Both properties may be modified by various means, 
 being increased, for instance, by moderate heat, and dimin- 
 ished by moderate cold, while by very high or by very low 
 temperatures they are entirely suspended. They are also 
 affected, in the way of reduction, by anaesthetics, narcotics 
 and mechanical compression. 
 
 . Nerve Stimuli. 
 
 The regular activities of nerves are carried on under the 
 influences of what may be termed their normal stimuli, in 
 contradistinction to stimuli employed artificially. 
 
 The normal stimuli vary for different nerves, the optic nerve 
 being stimulated by light waves, the auditory nerve by sound 
 waves, the olfactory nerve by odoriferous substances" in the 
 form of gas, and the gustatory nerves by sapid substances in 
 solution, while the other afferent nerves are stimulated by 
 such agencies as pressure, heat, cold, etc., according to the 
 special stimulus to which they are each adapted, by their 
 
20 GENERAL 8TRVCTVRB OF THE NERVOUS SYSTEM. 
 
 peripheral endirgs, to respond. The normal stimuli of the 
 afferent nerves act first on the structures in which these 
 nerves have their peripheral terminations, that is, on the 
 sensory end-organs, and these in turn act on the nerve-fibers. 
 The efferent nerves are normally stimulated at the nerve- 
 centers, either by an inflow of impulses through the afferent 
 nerves, or by impulses originating in the cortex of the cere- 
 brum or other parts of the brain. 
 
 The artificial stimuli capable of affecting the activity of 
 nerves are of four kinds, chemical, electrical, thermal and 
 mechanical. Any of these agencies applied to a nerve will 
 produce some change in the activity of its fibers, depending 
 on the manner in which they affect one or both of its proper- 
 ties of irritability and conductivity. 
 
 Nerve Impulses. 
 
 In the efferent nerves of the voluntary muscles the im- 
 pulses are transmitted with a velocity approximating one 
 hundred and twelve feet per second, and discharged from the 
 nerve-centers at an average rate of ten per second. The rate 
 of discharge, however, varies in different individuals, in dif- 
 ferent nerves, and in the same nerve under different circum- 
 stances, a rate as high as twenty or more per second not being 
 uncommon in some of the finer and more delicate muscular 
 inovements. The strength of the motor impulses may be 
 modified at will, within certain limits, and both the strength 
 and velocity may be affected by any of the agencies that pro- 
 duce alterations in the irritability and conductivity of nerves, 
 being either increased or decreased according to the action of 
 the agency on these properties. The strength alone is some- 
 times modified in the same ratio as the intensity of the 
 stimulus, though this is not an invariable rule. Very fre- 
 quently the intensity of the stimulus and the movement it 
 provokes are out of all proportion. 
 
 So far as known the quality of nerve impulses is the same 
 
DEGENEBA TION AND BEGENEBA TION. 2 1 
 
 in all nerves, and the difierent effects which they produce in 
 nerves of different functions is due to a difference either in 
 the mode of ending of the nerves or in the kind of tissue in 
 which they end. Motor and inhibitory nerves, for example, 
 conduct the same kind of impulses, but produce different 
 effects on muscle because they end differently in the muscle- 
 cells, and afferent and efferent nerves produce different effects 
 because of a difference in their terminal tissiies. 
 
 Nerve Degeneration and Regeneration. 
 
 A nerve-fiber is a branch of a nerve-cell and dependent for 
 its nutrition and physiological integrity upon connection 
 with the cell from which it originates. Any part of a nerve- 
 fiber cut off from its cell soon degenerates and dies. In a 
 peripheral nerve when cut the fibers on the distal side of the 
 section break up into fragments and are finally absorbed by 
 the lymphatics. But during this process the nuclei of the 
 neurilemmal sheath multiply and, in the place of the origi- 
 nal fiber, form a new strand of protoplasm called an embryonic 
 or hand fiber. If connection is now established between the 
 band fiber and the central stump of the original fiber, the 
 band fiber, brought under the nutritive influence of the 
 nerve-cell, eventually develops into a complete new nerve- 
 fiber, of which the axis-cylinder process is believed to be a 
 development from the central stump. 
 
 On the central side of the section the fiber undergoes 
 degeneration for a few internodal segments, but regenerates 
 again in the same way as the fiber on the peripheral side. 
 The nerve-cell is also affected, undergoing swelling and a loss 
 of Nisl's granules. These changes begin almost immediately 
 after the section and continue for about three weeks, when 
 restoration begins and the cell finally regains its normal con- 
 dition. In course of time, however, unless the fiber is re- 
 stored 9,nd its functions resumed, both the cell and the 
 
22 GENERAL STRUCT OBE OF THE NERVOUS SYSTEM. 
 
 attached segment of fiber undergo degenerative changes that 
 are chronic, or what is known as atrophy from disuse. 
 
 Regeneration of nerve-fibers is confined to the periphery. 
 In the central nervous system, where the neurilemma! sheath 
 is lacking, regeneration never takes place. 
 
PART II. 
 
 THE STRUCTURE AND FUNCTIONS OF THE 
 CENTRAL NERVOUS SYSTEM. 
 
PJjAtb 1. 
 
 fbe oprebrum viewed from above.— (Mpdifled from Spaltebolz.) 
 
CHAPTER I. 
 
 THE CEREBRUM. 
 
 The cerebrum is the largest and uppermost part of the 
 brain and occupies the greater part of the cranial cavity. It 
 consists of lateral halves, called hemispheres, between which 
 is the longitudinal fissure. In front and behind, this fissure 
 forms a complete separation, but at the middle twoTfourths 
 of its lower half it is interrupted by the corpus callosum, 
 which extends from one hemisphere to the other and forms 
 their chief connecting bond. Below the corpus callosum the 
 separation is continued by the third ventricle, a narrow, 
 vertical crevice bounded on each side by the optic thalamus. 
 Each hemisphere presents three surfaces, the mesial, the 
 outer and the lower. The mesial surface is flat and the outer 
 surface is convex. The lower surface is of varied conforma- 
 tion. Its front part, which lies in the anterior cranial fossa, 
 is flat and horizontal. Its middle part, which lies in the 
 middle cranial fossa, is irregular and slopes downward and 
 outward from the median line. Its hind part, which over- 
 lies the cerebellum, is irregular and sloping. 
 
 THE GRAY MATTER OF THE CEREBRUM. 
 
 The gray matter of the cerebrum comprises the cortex, 
 which covers the surface of each hemisphere, and several 
 masses embedded in the hemispheres at their base. These 
 latter are the amygdala, the caudate nucleus, the lenticular 
 nucleus, the claustrum and the optic thalamus. 
 
 (25) 
 
26 THE CEBEBBUM. 
 
 The Cortex. 
 
 The cortex is arranged in more or less distinct layers, the 
 cells of which vary in size and form and in the destination of 
 their processes. 
 
 The first or molecular layer, lying at the surface, contains 
 small cells the processes of which run in the gray matter and 
 end in the layer in which they arise. Their dendrites re- 
 ceive the terminal arborizations of fibers coming from other 
 regions, and their axons arborize either about cells of their 
 own layer or about the dendritic processes that extend out- 
 ward from cells in the layers underneath. These cells may 
 be considered as the receivers and distributors of impulses, 
 many of the impulses received coming through afferent 
 neurons and being distributed to efferent neurons. They are 
 classed as association cells and are generally considered as 
 the part of the brain in which the higher and more important 
 mental processes are mediated. 
 
 The second layer contains small cells, pyramidal in form, 
 with the apex directed towards the surface. Their dendrites 
 arise from the apex and end in the molecular layer. Their 
 axons arise from the base and terminate somewhere in the 
 gray matter, many of them dividing into branches that run 
 at right angles to the main stem. 
 
 The third layer, also, contains pyramidal cells, but of a 
 larger type than those in the second layer. Their dendrites 
 extend outward and end in the first layer, but their axons 
 enter the white matter of the interior of the hemispheres, 
 those that arise in the motor areas ultimately forming the 
 pyramidal tracts in the spinal cord. 
 
 The fourth layer is composed of small cells of irregular and 
 varied conformation, the processes of which, both dendrites 
 and axons, terminate in the gray matter of the cortex. 
 
 The fifth layer contains small, irregular cells, the dendrites 
 of which terminate in the pyramidal layers, while their axons 
 enter the white matter of the interior. 
 
GRAY MATTER OF THE CEREBRUM. 27 
 
 The Amygdala and the Caudate Nucleus. 
 
 The amygdala is a small, thickened area of the cortex, 
 lying at the apex of the temporal lobe, not far from the 
 under surface of the hemisphere. Continuous with it is a 
 narrow, oval-shaped band of nerve-tissue, which forms the 
 caudate nucleus. This at first runs backward in the lower 
 part of the lateral ventricle. Then curving upward to the 
 roof of the ventricle, it runs forward to the front of the ven- 
 tricle and expands into a large pyramidal mass, which forms 
 the lenticular nucleus. On its median border is a band of 
 nerve-fibers termed the taenia semidrcularis. 
 
 The Lenticular Nucleus. 
 
 The lenticular nucleus, extending deeply into the sub- 
 stance of the hemispheres, presents a rounded base that faces 
 outward, and an apex that points inward. In front and 
 below, it is continuous with the caudate nucleus, but in 
 other parts it is separated from it by a thick layer of fibers, 
 which forms the internal capsule. 
 
 The Claustrum. 
 
 The claustrum is a thin layer of polymorphic cells which 
 have become separated, by a layer of white matter, from the 
 island of Rail. It is situated outside the lenticular nucleus, 
 and is continuous with it at the anterior part of its lower 
 border. In other parts the two structures are separated by 
 ■ the external capsule. 
 
 The Optic Thalamus. 
 
 The optic thalamus is the largest of the gray masses. It 
 is situated farther back than the lenticular nucleus, and is 
 separated from it by the internal capsule. Though embedded, 
 for the most part, in the hemisphere, its flat, mesial surface 
 forms a side wall of the third ventricle, and a part of its 
 rounded, upper and posterior surfaces lies under the ven- 
 
28 THE CEREBRUM. 
 
 tricular roof. On its upper surface, in front, is a small 
 elevation, called the anterior tubercle, and on the rear of this 
 surface is another prominence which continues back to the 
 posterior surface and is known as the pulvinar. The two 
 thalami are connected by two commissures: the middle, which 
 crosses the third ventricle at about its center; and the pos- 
 terior, which crosses farther back. 
 
 THE FISSURES, LOBES AND CONVOLUTIONS OF 
 THE CORTEX. 
 
 The surface of the cortex presents many grooves or fissures, 
 which, though not unvarying, are of sufficient regularity to 
 serve as the boundary lines of fairly uniform and constant 
 divisions. These fissures divide the surfaces of the hemis- 
 pheres into lobes, and the lobes into convolutions or gyri. 
 
 The Outer Surface. 
 
 Three fissures, the central. Sylvian and parieto-occipital, 
 divide the outer surface into the frontal, parietal, occipital 
 and temporal lobes. 
 
 The central fissure or the fissure of Rolando begins at about 
 the middle of the upper margin of the hemisphere and runs 
 downward and a little forward, dividing the surface into two 
 nearly equal parts. 
 
 The Sylvian fissure, beginning about the middle of the lower 
 surface and extending upward and backward as a deep cleft, 
 cuts through to the outer surface and forms the anterior and 
 the posterior limb. The anterior limb is short and runs for- 
 ward ; the posterior limb is much longer and runs upward 
 and backward, ending about two-thirds of the way from the 
 front to the back of the hemisphere and about half way from 
 the vertex to the base. 
 
 The parieto-ocdpital fissure begins far back on the upper 
 margin of the hemisphere and runs downward and forward 
 on the mesial surface, cutting off a triangular area at its pos' 
 
THE OtlTER SURFACE OF THE CEREBRUM. 29 
 
 terior end. On the outer surface it is conceived as an imag- 
 inary line running in the same plane with the fissure and 
 ending at the pre-occipital notch. 
 
 The frontal lobe comprises the area lying in front of the cen- 
 tral fissure and above the Sylvian. Its convolutions are the 
 pre-central and the first, second and third frontal. The pre- 
 central convolution is situated in front of the central fissure, 
 occupying a narrow, elongated area that extends from the 
 posterior limb of the Sylvian fissure to the upper margin of 
 the hemisphere. Its anterior boundary is the pre-central 
 fissure. The first frontal convolution lies along the antero- 
 superior margin of the hemisphere, with the second and third 
 convolutions in numerical order below. The third convolu- 
 tion extends down to the Sylvian fissure, the anterior limb_ 
 of which it contains. 
 
 The parietal lobe is an area of somewhat irregular outline, • 
 extending from the central fissure back to the parieto-occipital 
 line and from the posterior limb of the Sylvian fissure to the 
 superior margin of the hemisphere. Its convolutions are the 
 post-central, superior parietal, supra-marginal and angular. 
 The post-central convolution — an area of about the same 
 dimensions and conformation as the pre-central — lies along 
 the posterior side of the central fissure; the superior parietal 
 convolution, along the upper border of the hemisphere ; the 
 angular convolution, in the postero-inferior angle of the lobe, 
 and the supra-marginal convolution, above the termination 
 of the posterior limb of the Sylvian fissure. 
 
 The occipital lobe is the triangular area lying behind the 
 parieto-occipital line. Its convolutions are the first, second 
 and third occipital, numbered from above downward. 
 
 The temvporal lobe lies in the lower part of the hemisphere, 
 with the frontal and parietal lobes above and the occipital 
 lobe behind. Its convolutions are the first, second and third 
 temporal. The first convolution is situated along the lower 
 border of the Sylvian fissure, with the second and third con- 
 volutions running parallel with it below. 
 
30 THE CEREBRUM. 
 
 The Mesial Surface. 
 
 The lobes of the mesial surface are the frontal, parietal and 
 occipital, all of which are continuations of the corresponding 
 lobes from the outer surface. 
 
 The frontal lobe is here continued in the marginal convolu- 
 tion, which runs along the lower, front and upper margin of 
 the hemisphere, to a point a short distance behind the begin- 
 ning of the central fissure. In the posterior end of this 
 convolution is a small quadrangular area described as the 
 para-central convolution. It extends beyond the frontal lobe 
 and invades the territory of the parietal. 
 
 The parietal lobe is continued on to the mesial surface in 
 the pre-cuneus convolution, a quadrangular area that lies 
 behind the para-central convolution and extends back to the 
 parieto-occipital fissure. 
 
 The occipital lobe is continued in the cuneus, a triangular 
 area bounded by the parieto-occipital fissure above and by 
 the calcarine fissure below, the two fissures meeting and 
 forming the apex of the triangle. 
 
 The remainder of the mesial surface is occupied by the 
 callosal convolution, which runs along the free surface of the 
 corpus callosum, separated from the marginal convolution 
 by the calloso-marginal fissure. Its posterior end is con- 
 tinuous with the hippocampal convolution, of the lower 
 surface, and the two convolutions form what is sometimes 
 termed the limbic lobe. 
 
 The Lower Surface. 
 
 On this surface the first, second and third frontal convolu- 
 tions are continued from the outer surface and extend back 
 as far as the Sylvian fissure, the first convolution lying next 
 to the great longitudinal fissure, and the others running 
 parallel with it at its outer side. 
 
 The remainder of this surface is occupied by the temporal 
 lobe and is often designated as' the tentorial surface, from its 
 
Plate 2. 
 
 <«»/,?/</»"" 
 
 Diagrammatic representations of the Assures and convolutions of (A) the outer surface 
 and (B) the iqesial surface, of the cerebrum, left hemisphere, 
 
THE INSULA AND THE INTERNAL CAPSULE. 31 
 
 resting on the tentorium, which lies between the cerebrum 
 and the cerebellum. Its convolutions are the bippocampal, 
 subcalcarine, subcollateral and third temporal. The bippo- 
 campal convolution borders the central region and extends 
 from the rear end of the corpus callosum to the Sylvian fis- 
 sure. The subcollateral convolution lies below the bippo- 
 campal and is separated from it by the collateral fissure. 
 The subcalcarine convolution lies below the cuneus, from 
 which it is separated by the calcarine fissure. The third 
 temporal convolution is a continuation of the same convolu- 
 tion from the outer surface. 
 
 The Insula. 
 
 The insula, otherwise known as the central lobe or the 
 island of Reil, is a part of the hemisphere which, in early 
 foetal- life, was superficial, but which was later crowded to 
 the interior by the more rapid development of the surround- 
 ing tissues. It is situated externally to the claustrum and 
 separated frrf^m it by a layer of white matter. Its cortex 
 looks towards the surface of the hemisphere and is marked 
 off from the adjacent tissues by the circular fissure. It 
 presents five convolutions, named numerically. 
 
 THE INTERNAL CAPSULE. 
 
 The internal capsule is a narrow, fore-and-aft slit in the 
 base of the hemisphere, through which nerve-fibers pass on 
 their way to and from the cortex of the cerebrum. It is 
 bounded externally by the lenticular nucleus, and mesially 
 by the caudate nucleus and the optic thalamus, and its gen- 
 eral direction from above is downward and towards the 
 median line. Near its middle is a bend formed by the 
 rounded apex of the lenticular nucleus and known as the genu, 
 which divides the capsule into an anterior a.nA a posterior limb. 
 Within the hemisphere the fibers that pass through the cap- 
 sule spread out in nearly every direction towards the cortex, 
 forming what is known as the corona radiata. 
 
32 THE CEREBRUM. 
 
 THE EXTERNAL CAPSULE. 
 
 The external capsule, smaller than the internal, lies be- 
 tween the lenticular nucleus and the claustrum. It is com- 
 posed in part of afferent fibers entering the cerebrum aad in 
 part of commissural fibers derived from the anterior com- 
 missure. 
 
 THE ANTERIOR COMMISSURE. 
 
 The anterior commissure is a bundle of fibers that con- 
 nects the front part of the temporal lobes. It crosses the 
 median line a little below and behind the front part of the 
 corpus callosum, and then, curving downward and backward, 
 passes through the lenticular nucleus to the external capsule, 
 from which it spreads out in the temporal lobe. 
 
 THE CORPUS CALLOSUM. 
 
 The corpus callosum is a solid band of commissural fibers 
 that run transversely and connect the corresponding parts of 
 the cortices of the hemispheres. These fibers consist to a 
 large extent of the axis-cylinder processes of cortical cells, 
 but they also comprise many collaterals from the efferent 
 projection fibers that pass through the internal capsule. They 
 connect all parts of the cortices except those connected by the 
 anterior commissure. The corpus callosum, into which they 
 are compressed as they cross the longitudinal fissure, has a 
 fore-and-aft measurement of about five inches and a thick- 
 ness of nearly an inch at the ends, but less in other parts. 
 In front it curves downward and backward and forms the 
 genu. The genu grows thinner as it continues backward and 
 finally presents a sharp extremity, called the rostrum. The 
 rear end bends downward and forms the splenium. The in- 
 termediate part is the body. From each side the fibers radiate 
 to the various parts which they connect. The fibers that 
 make up the genu radiate in the frontal lobe and form the 
 forceps anterior; those that make up the splenium radiate 
 in the occipital lobe and form the forceps posterior ; those that 
 
ASSOCIATION FiBEM AND THE FORNIX. 33 
 
 form the body radiate in the remaining parts, and those pass- 
 ing to the temporal lobe form a plate called the iapetum. 
 These commisural fibers interlace with the projection fibers, 
 and the two sets of fibers constitute the white matter of the 
 interior of the hemisphere. 
 
 THE ASSOCIATION FIBERS. 
 
 The association fibers connect different parts of the cortex 
 and associate its various activities, their origin, course and 
 destination all being in the cortical gray. They are grouped 
 in bundles, which vary in length from those connecting ad- 
 joining convolutions to those connecting different lobes. The 
 longer of these bundles are the following : 
 
 (a ) The uncinate, connecting the third frontal convolution 
 with the uncinate process of the hippocampal convolution. 
 
 (b) The superior longitudinal, connecting the middle of the 
 frontal lobe with the upper part of the occipital lobe and the 
 anterior part of the temporal lobe. 
 
 (c) The inferior longitudinal, connecting the anterior part of 
 the temporal lobe with the lower part of the occipital lobe. 
 
 (d) The stria longitudinales, running in the callosal convo- 
 lution and connecting the Sylvian region in front with the 
 hippocampal convolution behind and below. 
 
 (e) The fornix, connecting the optic thalamus with the un- 
 cinate process of the hippocampal convolution. 
 
 Structure of the Fornix. 
 
 The fornix is situated under the corpus callosum, attached 
 to its under surface behind, but separated from it above and 
 in front by the septum lucidum. It consists of lateral halves 
 united in the middle, the union of these parts forming the 
 body of the structure. In front it takes a curving course 
 downward and forward, and the halves, becoming separated, 
 form the anterior pillars. Each pillar continues the curving 
 course and finally reaches the under surface of the cerebrtim. 
 3 
 
34 TEE CEREBRUM. 
 
 Here the pillar bends on itself and forms a loop known as 
 the corpus albicans or the corpus mammillare, after which it runs 
 upward as the bundle of Vicq-d'Azyr and ends in the optic 
 thalamus. The halves, also becoming separated behind, here 
 form the posterior pillars. These are connected with each 
 other by a thin band of fibers, called the lyra, and externally 
 they are bordered by fibers tha,t continue along the body of 
 the structure and form the fimbria,. Each pillar bends 
 downward, backward and outward and then runs forward, 
 ending in the hippocampal convolution and the neighboring 
 gray. 
 
 THE SEPTUM LUCIDUM. 
 
 This structure, which lies between the fornix and the cor- 
 pus callosum, forms the partition between the lateral ven- 
 tricles. It consists of two thin layers of nerve-tissue, an 
 outer of white and an inner of gray, inclosing a narrow 
 crevice, which contains serous fluid and has no communica- 
 tion with any other cavity of the brain. 
 
 THE LATERAL VENTRICLES. 
 
 In each hemisphere of the cerebrum is an irregularly 
 shaped cavity extending in a general fore-and-aft direction 
 and forming the lateral ventricle. It consists of a main part 
 or body, with a forward and outward projection in front, 
 called the anterior horn, a backward projection behind, called 
 the posterior horn, and a third projection which extends 
 downward, outward and forward and forms the middle horn. 
 Each lateral ventricle communicates with the third ventricle 
 by means of an opening situated near the front of the body 
 and known as the porta or the foramen of Munro. 
 
 THE THIRD VENTRICLE. 
 
 This is a narrow, vertical crevice, situated below the fornix 
 and in line with the longitudinal fissure. It is bounded in 
 front by the anterior pillars of the fornix, above by the body 
 
PliATE 3. 
 
 The brain as seen from below and in front : 1, olfactory bulb ; 2, olfactory tract ; 3, 
 optic nerre ; 4, optic chiasm ; 5, oculomotor nerve ; 6, trochlear nerve ; 7, abducent 
 nerve ; 8, Gasserian ganglion ; 9, 10, trifacial nerve ; 11, auditory nerve ; 12, facial 
 nerve ; 13, glosso-pharyngeal and vagus nerves ; 14, hypo-glossal nerve ; 15, spinal acces- 
 sory nerve ; 16, first cervical nerve ; 17, second cervical nerve ; 18, hypophysis ; 19, optic 
 tract ; 20, corpus albicans ; 21, pons ; 22, oblongata ; 23, cerebellum ; 24, decussation of 
 pyramids.— ^Modified fromSpalteholz.) 
 
PHYSIOLOGICAL AREAS OF THE CORTEX. 35 
 
 of the fornix, and laterally by the optic thalami. Behind it 
 are the epiphysis, the posterior end of the callosum, the 
 posterior commissure, and the opening of the aqueduct which 
 connects it with the fourth ventricle. It is crossed by the 
 middle commissure, and in the front part of its floor are the 
 corpora albicantia and the hypophysis. 
 
 PHYSIOLOGICAL AREAS OF THE CORTEX. 
 
 (1) The Motor Area, which controls the voluntary 
 movements, extends over the para-central and pre-central 
 convolutions. The uppermost part of this area— the para- 
 central convolution and the upper end of the pre-central — 
 controls the movements of the legs and trunk; and below 
 this come in succession the areas that control the movements 
 of the arm and hand, the neck, the head and eyes, and the 
 face, mouth and throat. Through the axons of its pyramidal 
 cells, this area is connected with the motor nuclei of the 
 cranial nerves and with the efferent spinal neurons whose 
 fibers are distributed to the voluntary muscles. 
 
 (2) The Sensory Areas are the cortical terminations of 
 the sensory paths and the centers in which sensations are felt 
 and interpreted. So far as these areas have been outlined 
 and the senses which they mediate discovered, they are as 
 follows: 
 
 (a) The body-sense area lies in the parietal lobe behind the 
 central fissure, occupying the post-central convolution and a 
 part of the superior parietal and supra-marginal convolutions. 
 It is connected with widely distributed afferent paths, and 
 the distinct senses which it mediates are, so far as known, 
 the sense of temperature, the sense of pressure, the sense of 
 touch and the muscle sense. 
 
 (b) The olfactory area, which mediates the sense of smell, 
 lies at the anterior end of the hippocampal convolution, 
 chiefly in its uncinate process. It is connected with the 
 olfactory end-organ in the nasal fossae, through the first 
 cranial nerve. 
 
36 THE CEBEBBUM. 
 
 (_c) The gustatory area, which mediates the sense of taste, 
 lies in the same convolution 'svith the olfactory area, being 
 situated directly behind it. It is connected with the taste- 
 buds through branches of the facial and glosso-pharyngeal 
 nerves. 
 
 (d) The vimal area, which mediates the sense of sight, lies 
 on the mesial surface of the occipital lobe, in the neighbor- 
 hood of the calcarine fissure. It is connected with the retina 
 through the second cranial nerve. 
 
 (e) The auditory area, in which all iijjpressions of sound 
 are received, is situated on the outer surface of the hemis- 
 phere, in the first temporal convolution. It is connected 
 with the ear through the eighth cranial nerve. 
 
 (3) The Motor Speech Area, or "Broca's convolu- 
 tion," is situated in the posterior part of the third frontal 
 convolution, its connections being with the motor area that 
 lies directly behind it and controls the movements of the 
 face, mouth and throat. In this area are recorded the mem- 
 ories of the motor innervations necessary for producing the 
 sounds habitually associated with the expression of words or 
 ideas. It is generally developed on only one side — on the 
 left side in the right-handed and on the right side in the left- 
 handed. Lesions in this area result in more or less loss of 
 the power to express thoughts in spoken language — a con- 
 dition termed motor aphakia. 
 
 (4) The Auditory Speech Area lies behind the audi- 
 tory area in the first temporal convolution. This area serves 
 as the center for recording the memories of words and sounds 
 heard and for associating them with the ideas which they 
 represent. Impressions produced on the auditory area are 
 here interpreted. Lesions in this area result in more or less 
 loss of the ability to understand spoken language — a form of 
 sensory aphasia known as word-deafness. 
 
 (5) The Visual Speech Area is situated on the outer 
 surface, in the angular convolution of the parietal lobe. In 
 
tliATl! 4. 
 
 occiPir'Jr 
 
 7?^^" 
 
 Diagrammatic representations of the outer surface of the left cerehral hemisphere : 
 A, showing the lohes ; B, showing the approximate location of the physiological 
 areas of the cortex. 
 
THE SENSES AND TBEIR PEBIPBERAL FIBEBS. 37 
 
 this area the memories of written or printed symbols are 
 recorded and such symbols are associated with their mean- 
 ings. Lesions in this area affect the power to understand 
 written or printed language-^a form of sensory aphasia termed 
 word-hlindness. 
 
 (6) The Writing Area is situated in the posterior part 
 of the second frontal convolution, adjoining the motor area 
 that lies behind it and controls the movements of the arm 
 and hand. In this area are recorded the memories of the 
 motor innervations necessary for forming the symbols by 
 which ideas are expressed in writing. Lesions in this area 
 cause agraphia — a loss of the power to write. Like the motor 
 speech area, the writing area is developed unilaterally, and 
 on the side opposite the trained hand. 
 
 (7) The Association Areas, which occupy the re- 
 mainder of the cortex, are three in number: the anterior 
 area, lying in front of the motor area; the posterior area, 
 lying behind the body-sense area; and the median area, or 
 the cortex of the island of Reil. Their connections are with 
 all the other areas of the cortex. Their function is to asso- 
 ciate sense impressions and record memories. They consti- 
 tute the organ of thought. 
 
 THE SENSES AND THEIR PERIPHERAL FIBERS. 
 
 Every distinct sense has, as its anatomical basis, what is 
 known as a sense-organ. This consists of three parts : a per- 
 ipheral structure or end-organ upon which the stimulus acts; 
 afferent fibers to conduct the impulses, and a cortical center 
 in which the sensation is finally produced. Besides the vis- 
 ual, auditory, olfactory and gustatory senses, each of which 
 is mediated through a single end-organ, there are other senses 
 which are quite as distinct and special as these, but of which 
 the peripheral organs and the mediating fibers are more or 
 less widely distributed. These are the sense of temperature 
 (heat and cold), the sense of pressure, the sense of pain, and the 
 
38 THE CEBEBRUM. 
 
 muscle sense. The fibers whose impulses give rise to the sen- 
 sations of temperature and pressure, are distributed in all the 
 cutaneous nerves and in the nerves supplying the mucous 
 membrane of the mouth and the lower part of the -rectum. 
 The fibers whose impulses produce sensations of pain, are 
 distributed in all peripheral parts of the body, being espe- 
 cially numerous in the nerves of membranes and the skin. 
 The skin areas, the stimulation of which will produce the 
 different cutaneous sensations, consist of mere points. They 
 are designated as "warm spots," "cold spots," "pressure 
 spots" and "pain spots." Each of these reacts only to its 
 own peculiar kind of stimulus. 
 
 The Muscle Sense is that by which we become con- 
 scious of the varying conditions in the voluntary muscles, 
 particularly the conditions that arise in connection with con- 
 traction. This sense is indispensable in the direction and 
 co-ordination of voluntary movements, and in this lies its 
 chief physiological value. The fibers concerned are a distinct 
 set, distributed to the muscles and tendons, and are estimated 
 to constitute from one-third to one-half of all the fibers in 
 the muscular branches of nerves. Their impulses produce 
 such sensations as those of weight and resistance, and, in 
 case of prolonged muscular effort, they also convey the sense 
 of fatigue. 
 
 The Sense of Touch, commonly counted as one of the 
 senses, is not a separate sense. A feeling of contact does not 
 arise apart from a sense of pressure, with which there may 
 also be associated a sense of heat or cold. Touch sensations 
 are generally composed of the pressure and temperature 
 elements. 
 
 The Sense of Hunger is mediated by nerves of the 
 stomach. But whether the fibers concerned are special or 
 general, whether they are distributed in the hning membrane 
 or the muscular coat, and what the acting stimulus is, are 
 questions to which, as yet, final answers cannot be given. 
 
MEMBRANES OF THE BBAIN. 39 
 
 The Sense of Thirst arises from the pharynx and is 
 mediated by nerves supplying the pharyngeal mucous mem- 
 brane. It is probable that the fibers which conduct the ex- 
 citing impulses are a distinct set, ending peripherally in a 
 special end-organ of thirst. 
 
 MEMBRANES OF THE BRAIN. 
 
 The cerebrum, as well as all other parts of the brain, is 
 surrounded by three meninges or membranes, all more or less 
 closely attached to one another and forming virtually a single 
 structure. 
 
 The inner membrane, known as the Pia or Pia Mater, is 
 a thin, delicate covering, consisting of blood-vessels supported 
 by areolar tissue. This is nutritive in function, and is 
 closely adherent to the entire surface of the brain, dipping 
 into all fissures and crevices and sending blood-vessels into 
 the underlying tissue. It also extends outward along the 
 nerve-roots and become continuous with the sheaths of the 
 nerves. The vascular structures, known as the choroid flex- 
 uses, are the fringed edges of the pial membrane projecting 
 into the cavities of the brain. Among these the plexus 
 known as the velum interpositum, which appears in the lateral 
 and third ventricles, is the most prominent. 
 
 The outer membrane, known as the Dura or Dura Mater, 
 is a thick, highly vascular membrane, of which, besides the 
 blood-vessels, white fibrous tissue is the main constituent. 
 Its outer surface is firmly attached to the cranial bones, of 
 which it forms the internal periosteum. The dura consists 
 of an inner and an outer layer, which, for the most part, are 
 in apposition. But in certain places the layers separate and 
 form channels or sinuses for the venous blood. This occurs 
 along the longitudinal fissure, along the fissure bet^veen the 
 posterior part of the cerebrum and the cerebellum, and along 
 the fissure between the cerebellar hemispheres. In each case 
 the two plates of the internal layer, after forming walls of the 
 
40 THE CEREBRUM. 
 
 sinus, reunite and project towards the center. In this way 
 are formed ihefalx cerebri, which projects into the longitudinal 
 fissure, the tentorium, which lies between the cerebrum and 
 the cerebellum, and the falx cerebelU, which enters the fissure 
 between the cerebellar hemispheres. By again separating 
 along their central edges, the layers of the falx cerebri and the 
 tentorium form other sinuses along the central structures of 
 the brain. The dura, like the pia, extends outward through 
 foramina at the base of the cranium and becomes continuous 
 with the sheaths of the nerves. 
 
 The third membrane, called the Arachnoid, lies between 
 the other two, to both of which it is more or less closely 
 attached by bundles of fibrous tissue. Between the arach- 
 noid and the dura is a space which, under normal condi- 
 tions, is only potential, but which sometimes becomes actual 
 in disease. It is called the subdural cavity. Between the 
 arachnoid and the pia is another space, more extensive than 
 the former and containing a little serous fluid. This is the 
 subarachnoid cavity. It is essentially a lymph space, and, by 
 means of openings into the fourth ventricle, is connected with 
 the brain cavities, which also subserve the same function. 
 The fluid contained in all these cavities, though resembling 
 lymph in its general character, is thinner than Ipmph and of 
 somewhat different constituents. It is designated as cerebro- 
 spinal fluid, being common to both, brain and spinal cord. 
 In some places, principally along the longitudinal fissure, the 
 arachnoid presents little outgrowths which press into the 
 dura and even make depressions in the bone. They are 
 termed Pacchionian bodies and often contain small particles 
 of calcareous matter, called "brain sand." 
 
 The membranes of the brain are innervated by sympathetic 
 fibers and by sensory fibers branching from the trifacial, 
 glosso-pharyngeal and pneumogastric nerves. 
 
CHAPTER II. 
 
 THE ISTHMUS CEREBRI. 
 
 Thk isthmus cerebri or midbrain extends downward and 
 backward from the base of the cerebrum to the upper end of 
 the pons, and connects the cerebrum with the lower parts of 
 the brain. Its main elements are fibers, but it also contains 
 some scattered collections of cells. Two columns of fibers, 
 the crura cerebri, converging from the base of the hemispheres, 
 are present on the anterior surface. Between them is a tri- 
 angular area that forms the posterior part of the interpedunc- 
 ular space. Four gray masses, the corpora quadrigemina, 
 mark the rear surface, and each lateral surface presents two 
 smaller masses, the corpora geniculata internum and externum, 
 or the internal and external geniculate bodies. 
 
 The isthmus is composed of lateral halves, with an inter- 
 mingling of transverse and longitudinal fibers and some cells 
 between them, the whole forming a median raphe or seam. 
 Each. half consists of the crusta, which forms its anterior part, 
 the tegmentum, which forms its posterior part, and the sub- 
 stantia nigra, a plate of gray matter between the crusta and 
 tegmentum. 
 
 The crusta is formed by efferent fibers that arise in the cor- 
 tex of the cerebrum and descend through the anterior limb 
 of the internal capsule. As nearly as their exact cortical 
 origin can be determined, the mesial fibers arise in the frontal 
 lobe, the outer fibers in the occipital and temporal lobes, and 
 the central fibers in the area that controls voluntary move- 
 ments. The outer group end by arborization in the gray 
 matter of the isthmus and pons; the central group enters the 
 
 (41) 
 
42 THE ISTHMTJS CEREBRI. 
 
 anterior pyramid of the oblongata; and the mesial group 
 have an uncertain ending, though it is probably, for the most 
 part, in nuclei of the oblongata. 
 
 The tegmentum presents a type of structure described as 
 formatio reticularis. It consists of longitudinal and transverse 
 fibers interlacing with each other and holding gray matter in 
 their meshes. Among the longitudinal fibers is one distinct 
 group, the •posterior longitudinal bundle, which is connected 
 with Deiters' nucleus and with the nuclei of the oculo-motor 
 and abducent nerves. It also extends downward through 
 the pons and oblongata into the antero-lateral tract of the 
 cord, where it is further connected with cells of the anterior 
 horns. The remaining longitudinal fibers are mainly afferent 
 fibers ascending from lower levels, either to end in the gray 
 matter at the base of the cerebrum, or to pass through the 
 internal capsule and end in the cerebral cortex. The major- 
 ity of the transverse fibers come from the cerebellum, by way 
 of the superior cerebellar peduncles. In the posterior part 
 of the tegmentum is the Sylvian aqueduct, which runs longi- 
 tudinally and connects the third and fourth ventricles of the 
 brain. 
 
 Besides the substantia nigra, the groups of gray matter in 
 the isthmus are: the lamina quadrigemina, which lies under 
 the quadrigeminal bodies; the red nucleus, which forms a 
 terminal station for some of the fibers in the superior cere- 
 bellar peduncle of the opposite side; and the oculo-motor 
 nucleus, the trochlear nucleus and the trifacial motor nucleus^ 
 which lie in the gray wall surrounding the Sylvian aqueduct. 
 
 The Corpora Quadrigemina. 
 
 The corpora quadrigemina are four rounded knobs of gray 
 and white matter, lying in the median region under the pos- 
 terior ends of the optic thalami. They consist of an upper 
 pair, the superior quadrigeminal bodies or the naies, and a 
 lower pair, the inferior quadrigeminal bodies or the testes. 
 
TSE COBPOBA QENICVLATA. 43 
 
 The two bodies of each pair are connected internally, but 
 superficially they are marked off by a longitudinal groove. 
 The pairs are separated by a transverse fissure. The superior 
 bodies serve as nuclei for some of the fibers in the optic 
 nerves, and the inferior bodies form one of the final relay 
 stations in the central course of the auditory nerves. 
 
 The Corpora Geniculata. 
 
 The internal and external geniculate bodies are small 
 masses of gray and white matter, lying at the sides of the 
 isthmus, the externsil body farther front and at a slightly 
 higher level than the internal. A bundle of optic nerve 
 fibers, the anterior brachium, runs back from the external 
 geniculate body to the superior quadrigeminal body and 
 unites the two structures. A bundle of commissural fibers, 
 the posterior brachium, unites in a similar manner the internal 
 geniculate body and the inferior quadrigeminal body. These 
 are fibers of Gudden's commissure, which runs round the 
 front of the isthmus with the optic nerves and connects the 
 inferior quadrigeminal and internal geniculate bodies of the 
 two sides. The external geniculate bodies are central nuclei 
 for some of the fibers in the optic nerves, and the internal 
 geniculate bodies are among the final relay stations in the 
 central course of the auditory nerves. 
 
CHAPTER III. 
 
 THE PONS. 
 
 The pons Varolii or the tuber annulare, commonly known 
 as the pons, extends from the isthmus to the oblongata, con- 
 necting not only these structures but other parts of the brain, 
 as well. Though containing a considerable quantity of gray 
 matter, its main elements are horizontal and vertical fibers. 
 The greater part of its horizontal fibers are derived from the 
 cerebellum, through the middle cerebellar peduncles, which 
 emerge from the cerebellum and run forward along each side 
 of the pons to its front, where they spread out and form its 
 anterior surface. In the front of the pons are tw-o vertical 
 bundles of fibers descending from the crustae of the isthmus 
 to the anterior pyramids of the oblongata, and behind these 
 descending bundles are two other vertical bundles ascending 
 from the oblongata to the isthmus and thence to the cere- 
 brum. These latter bundles are the lemnisci or the fillets, which 
 form the sensory path between the spinal cord and the brain. 
 
 The region behind these vertical bundles constitutes the 
 tegmentum, of the pons, which is continuous with the corre- 
 sponding region of the isthmus and like it in formation. It 
 contains some distinct groups of fibers and most of the pontal 
 gray matter. In its lower and anterior part are fibers that 
 run from one side of the pons to the other and form the trape- 
 zium or the corpus trapezoideum, which lies in the central 
 course of the auditory nerves. Farther back is the posterior 
 longitudinal bundle, continued down from the isthmus. 
 There are also numerous afferent fibers coursing upward 
 from lower levels to the cerebrum, and the roots of cranial 
 ■ (44) 
 
POSTERIOR SURFACE OF THE PONS. 45 
 
 nerves running in various directions between their nuclei and 
 the surface of the pons. The gray matter comprises the 
 motor and sensory nuclei of the fifth nerve, the nuclei of the 
 sixth, seventh and eighth nerves, and the trapezoidal and 
 superior olivary nuclei, which receive the terminal arboriza- 
 tions of the trapezial fibers. There are also a few smaller 
 collections of cells that have no individual names. 
 
 The posterior surface of the pons is concealed by the 
 superior cerebellar peduncles and a plate of nerve-tissue that 
 stretches between them, the peduncles running upward and 
 forward and converging at the lower border of the quadri- 
 geminal bodies. The plate of nerve-tissue, triangular in 
 shape, consists of an outer layer of gray and an inner layer 
 of white, and is variously referred to as the valvula, the valve 
 of Vieussens and the anterior medullary velum. Under the val- 
 vula and the mesial border of the peduncles lies the posterior 
 surface of the pons, which forms the upper part of the floor 
 of the fourth ventricle. 
 
CHAPTER IV. 
 
 THE CEREBELLUM. 
 
 The cerebellum is an ovoid mass, lying in the posterior 
 cranial fossa and beneath the posterior end of the cerebrum, 
 from which it is separated by a dural projection, termed the 
 tentorium. In front of it are the isthmus, pons- and oblongata, 
 with all of which it is physiologically related. It presents a 
 comparatively flat upper surface and a rounded lower sur- 
 face, which meet behind at the transverse fissure. Though one 
 continuous structure, it is considered as consisting of lateral 
 hemispheres and a median segment termed the vermis. On 
 the upper surface the vermis appears as a rounded elevation 
 running fore and aft through the middle and bounded on 
 each side by a groove that marks it off from the adjacent 
 hemisphere. On the lower surface the vermis is nearly con- 
 cealed in the valleaila, a deep depression which here forms the 
 dividing line between the hemispheres. Both surfaces are 
 marked by fissures that run in a generally transverse direc- 
 tion and cut deeply into the tissue, dividing it into segments 
 or folia: 
 
 On the upper surface the folia are continuous through the 
 vermis and the hemispheres. The folia of the vermis, from 
 front to back, are the lingula, the central lobe, the culmen, 
 the clivus and the cacumen. The corresponding folia of the 
 hemispheres are the frenulum, the ala, the anterior crescentic 
 lobe, the posterior crescentic lobe and the postero-superior 
 lobe. 
 
 On the lower surface the folia are not continuous through 
 the different parts and the arrangement is more complicated. 
 
 (46) 
 
TEE CEBEBELLAB GRAY MATTER. 47 
 
 Here the folia of the vermis, from front to back, are the 
 nodule, the uvula, the pyramid and the posterior tuber. 
 The folia of . the hemispheres, in the same order, are the 
 flocculus, the amygdala, the digastric lobe, the slender lobe 
 and the postero-inferior lobe. 
 
 The Cerebellar Gray Matter comprises the cortex, the 
 nucleus dentatus, the nucleus emboliformis, the nucleus 
 globosus and the nucleus fastigii. 
 
 The cortex covers the surface of the cerebellum and extends 
 inward along the fissures. Its cells are arranged in three 
 layers, an outer or molecular layer, an inner or granular 
 layer, and a middle layer consisting of Purkinje cells. The 
 connections of the cells of the different layers are as follows: 
 The dendrites of the Purkinje cells pass outward in numerous 
 branches and end in the molecular layer. The axons from 
 the cells in the molecular layer either remain in the layer 
 and connect with the dendrites of the Purkinje cells, or they 
 pass to the middle layer and arborize about their bodies. 
 The axons from the cells of the granular layer pass out to the 
 molecular layer and divide into two branches, which run at 
 right angles to the parent stems. The branches connect in 
 part with the dendrites of Purkinje cells and in part with 
 cells of the layer. 
 
 The dentate nucleus lies in the center of the hemisphere. It 
 consists of an outer layer of gray matter surrounding an 
 interior of white. On its median surface is an opening 
 through which the fibers from its gray matter make their 
 exit. 
 
 The remaining nuclei are smaller masses and are situated 
 in the vermis. 
 
 The Cerebellar White Matter consists of a central 
 part, termed the trapezium, with extensions into the folia, the 
 entire mass resembling a cedar tree and being known as ike 
 arbor vitse or the "tree of life." It is composed in part of 
 efferent fibers derived from the Purkinje cells of the cortex, 
 
48 THE CEREBELLUM. 
 
 and in part of afferent fibers derived from the pons, oblongata 
 and spinal cord. Of the afferent fibers some pass to the 
 molecular layer and end in direct contact with the dendrites 
 of the cells of Purkinje. The remaining afferent fibers end 
 about the cells of the granular layer, but are probably con- 
 nected with the Purkinje cells, through these intervening 
 neurons. 
 
 PHYSIOLOGICAL RELATIONS OF THE CEREBELLUM. 
 
 All connections of the cerebellum with other parts of- the 
 brain and with the spinal cord are formed through its supe- 
 rior, middle and inferior peduncles. 
 
 (1) Fibers arising from the cells of Purkinje course forward 
 in the middle cerebellar peduncles to the pons, where they 
 cross to the opposite side and end in the pontal nuclei. 
 Fibers from the nuclei ascend through the isthmus and 
 internal capsules and terminate in the motor areas of , the 
 cerebrum, thus completing a path through which each cere- 
 bellar hemisphere may affect the motor discharges from the 
 opposite hemisphere of the cerebrum. 
 
 (2) Other fibers arising from the cells of Purkinje end in 
 the dentate nuclei, from which new fibers, forming a second 
 relay, run forward in the superior peduncles to the isthmus, 
 where they cross to the opposite side and end, some termi- 
 nating in the red nucleus and the remainder in the optic thala- 
 mus. The fibers arising in the red nucleus cross to the 
 opposite side and descend in the rubrospinal tract of the cord, 
 where they end in relation with the efferent neurons of the 
 voluntary muscles, completing a path through which, with 
 its double crossing, each hemisphere of the cerebellum may 
 affect the action of the motor nerves of the same side of the 
 cord. Before the superior peduncles cross in the isthmus 
 they each give rise to a branch called Cajal's descending cere- 
 bellar bundle. These descend without crossing, and, by 
 means of collaterals, connect the cerebellum with the motor 
 
PHYSIOLOGICAL RELATIONS OF THE CEREBELLUM. 49 
 
 nuclei of the cranial nerves. The destination of the path 
 through the optic thalamus is undetermined. 
 
 (3) Afferent fibers entering the cerebellum by way of the 
 superior peduncles and the restiform bodies form connections 
 by which the cerebellum receives impulses from the end- 
 organ of equilibrium and the muscles, and perhaps, also, to 
 some extent, from the skin. 
 
 Through these various connections the cerebellum exerts a 
 co-ordinating influence on the movements of the voluntary 
 muscles — particularly the movements involved in locomotion 
 and the maintenance of equilibrium. 
 
 Note. — For the origin and course of the afferent paths to 
 the cerebellum, see pages 62, 63. 
 4 
 
CHAPTER V. 
 
 THE OBLONGATA. 
 
 The oblongata, otherwise known as the medulla and the 
 spinal bulb, lies on the basilar process of the occipital bone. 
 It is about an inch in length, and extends from the pons to 
 the spinal cord, with both of which it is continuous. Its 
 lower half is cylindrical in form, like the cord, and resembles 
 the cord in formation. Its upper half is widened trans- 
 versely, somewhat flattened from front to back, and con- 
 structed in a manner peculiar to itself. 
 
 The Anterior Surface of the oblongata is marked in the 
 middle by a longitudinal groove called the anterior median 
 fissure, which is an upward continuation of the fissure of the 
 same name in the spinal cord, and which here separates two 
 white masses known as the anterior pyramids. Each pj'ramid 
 is bounded laterally by the antero-lateral fissure, which has no 
 counterpart in the cord but is in line with the superficial 
 origins of the anterior roots of the spinal nerves. In the 
 upper half of the oblongata this fissure forms the dividing 
 line between the pyramid and an oval-shaped mass called the 
 inferior olive. The pyramids consist of efferent fibers which 
 arise in the motor areas of the cerebrum and descend through 
 the isthmus and pons to the oblongata. In the lower part of 
 the oblongata the greater part of these fibers — generally from 
 ninety to ninety-seven per cent. — cross from one pyramid to 
 the other, forming the pyramidal decussation. The remaining 
 fibers descend without crossing and form the direct pyramidal 
 tract of the spinal cord. In a few cases — about eleven per 
 cent. — the pyramidal decussation is complete and the direct 
 pyramidal tract is then wanting. 
 
 (50) 
 
THE SURFACES OF THE OBLONGATA. 51 
 
 The Posterior Surface is largely formed by an upward 
 continuation of the columns and fissures of the cord, but the 
 columns undergo changes in name and form on reaching the 
 oblongata. What is termed in the cord the postero-median 
 column becomes, in the lower half of the oblongata, the fasci- 
 culus gracilis, at the upper end of which is a group of cells, 
 the_ nucleus gracilis, corresponding to an enlargement called 
 the clava. From the middle of the oblongata the two fasciculi 
 diverge and run upward and outward through the upper half, 
 being here known as the posterior pyramids. The postero- 
 lateral column of the cord, on reaching the oblongata, be- 
 comes the fasciculus cuneatus, which lies at the outer side 
 of the fasciculus gracilis and is capped by the nucleus cuneatus. 
 This surface also presents the fasciculus of Rolando, a rounded 
 longitudinal elevation produced by the expansion of the sub- 
 stantia gelatinosa, which is continued upward from the tip of 
 the posterior horn of the cord. It extends through the 
 lower half of the oblongata and lies at the outer side of the 
 fasciculus cuneatus, with which it finally blends. Its upper 
 end contains the nucleus af Rolando, which corresponds to a 
 superficial prominence called the tubercle of Rolando. At the 
 outer side of each posterior pyramid lies the large bundle of 
 fibers which forms the restiform body or the inferior cerebellar 
 peduncle. The triangular area between the posterior pyra- 
 mids is continuous with the posterior surface of the pons and 
 forms the posterior half of the floor of the fourth ventricle. 
 The downward-pointing apex of the triangle is called the 
 calamus scriptorius. 
 
 The Lateral Surfaces are formed by the upward con- 
 tinuation of the lateral columns of the cord. They are each 
 bounded in front by the antero-lateral fissure, and behind by 
 the postero-lateral fissure. 
 
 The Internal Structure of the oblongata exhibits 
 marked changes in passing from the lowest level upward. 
 At the lower extremity the gray matter is centrally located 
 
52 TSE OSLOls^GATA. 
 
 and forms a single mass. Above this the gray is gradually 
 invaded by the white and divided by it into smaller and 
 smaller masses, some of which approach the surface in the 
 floor of the fourth ventricle. 
 
 The first pronounced change in arrangement is seen at the 
 pyramidal decussation, where the crossing fibers, running at 
 first horizontally from one pyramid to the other and then 
 obliquely backward to the lateral columns, sever the heads 
 of the anterior horns, each head henceforth forming the lateral 
 nucleus. . Here, too, the posterior horn becomes thicker and 
 turns outward, and the nucleus gracilis appears, projecting 
 backward from its base. 
 
 Above the pyramidal decussation a change occurs in the 
 posterior region similar to the preceding in the anterior 
 region. Here the posterior horn presents a new structure, 
 the nucleus cuneatus, which also projects backward from its 
 base, outside the nucleus gracilis. These two nuclei give rise 
 to a bundle of fibers that constitutes the greater part of the 
 lemniscus or fillet. This runs horizontally forward and in- 
 ward across the median line to the back of the opposite 
 anterior pyramid, where some of the fibers turn upward 
 towards the cerebrum. In their forward passage the two 
 fillets each sever the head of the posterior horn of their own 
 side, and form with each other, at the mid-line, a criss-cross 
 of fibers called the sensory decussation or the crossing of the fillets. 
 
 From this level upward the important changes are more in 
 the position of the gray matter than in its division. The 
 nucleus gracilis begins to curve outward and to come nearer 
 and nearer to the surface, and at the upper end of the ob- 
 longata it is blended with the posterior horn, the resulting 
 mass lying near the median line in the floor of the fourth 
 ventricle. The nucleus cuneatus retains its identity and is 
 more deeply situated in the interior. 
 
 The anterior area of the oblongata contains a little gray 
 and much white, the white consisting principally of the 
 
TBE GRAY MATTER OF THE OBLONGATA. 53 
 
 pyramids and the fillets. The lateral and posterior areas 
 consist of longitudinal and horizontal fibers and many collec- 
 tions of cells. They are often referred to as the tegmentum. 
 The Gray Matter comprises the following groups: (1) 
 the cells whose fibers form the first cervical nerve; (2) the 
 nucleus ambiguus, which extends nearly the entire length of 
 the oblongata and gives origin to the motor fibers of the 
 ninth and tenth nerves and to the spinal fibers of the eleventh 
 nerve; (3) the hypoglossal nucleus, which also extends nearly 
 the entire length of the oblongata and gives origin to the 
 twelfth nerve; (4) a long column of cells that serves as the 
 sensory nucleus of the seventh, ninth and tenth nerves ; (5) 
 the dentate nucleus, which lies in the interior of the inferior 
 olive and gives rise to fibers that join the inferior cerebellar 
 peduncles and pass to the cerebellum ; (6) the vaso- constrictor 
 center which lies near the median line in the floor of the 
 fourth ventricle ; (7) the cardio- inhibitory center, which is 
 closely related to the nucleus ambiguus and probably forms 
 a part of it ; (8) the respiratory center, which lies at the level 
 of the calamus scriptorius ; (9) the nucleus gracilis, which 
 forms the terminal station for the main fibers that ascend in 
 the postero-median column of the cord, and (10) the nucleus 
 cuneatus, which forms the terminal station for the main fibers 
 that ascend in the postero-lateral column of the cord. 
 
 DISTRIBUTION OF THE FIBERS FROM THE NUCLEI 
 GRACILIS AND CUNEATUS. 
 
 A few of the fibers that arise in these nuclei — the posterior 
 external arcuate fibers — pass directly to the cerebellum, through 
 tlie inferior cerebellar peduncle of their own side. The great 
 majority, however, cross in the decussation of the fillets to 
 the opposite side of the oblongata. Of these fibers those 
 known as the anterior external arcuate fibers continue forward 
 to the anterior surface of the oblongata, and then, winding 
 outward round the anterior pyramid and the inferior olive, 
 pass to the cerebellum by way of the inferior cerebellar 
 
54 THE OBLONGATA. 
 
 peduncle of the side opposite to their origin. The rest of the 
 decussating fibers — the internal arcuate fibers — turn upward 
 behind the anterior pyramid and form the lemniscus or fillet, 
 which courses upward to the cerebrum. In the oblongata 
 and pons the fillet receives some accessions from the sensory 
 nuclei of cranial nerves, and in the isthmus it is further aug- 
 mented by fibers from the spinal tract of Gowers. The fillet 
 eventually reaches the cortex of the cerebrum, in part directly 
 and in part through fibers from the optic thalamus. Its 
 cortical terminations are about association neurons. It forms 
 the main sensory channel through which impulses from each 
 side of the body reach the opposite side of the brain. 
 
 THE FOURTH VENTRICLE. 
 
 The fourth ventricle presents a roof, a floor, an upper 
 angle, a lower angle and two lateral angles. The roof is 
 formed in front by the superior cerebellar peduncles and the 
 intervening valvula, and behind by the inferior cerebellar 
 peduncles and an intervening projection of the pial mem- 
 brane, termed the metatela. The valvula and the metateld 
 are continuous with the cerebellum, through the lingula and 
 the nodule, respectively. The floor, which slopes downward 
 and backward from above, is formed in its upper part by the 
 ■ posterior surface of the pons, and in its lower part by the 
 posterior surface of the upper part of the oblongata. It is 
 rhomboidal in form, with the angles at the endfe and sides. 
 Its upper boundaries are the superior cerebellar peduncles, 
 and its lower boundaries are the posterior pyramids of the 
 oblongata. The lower angle, formed by the pyramids, lies 
 at the upper end of the central canal of the spinal cord. The 
 upper angle, formed by the superior peduncles, lies at the 
 lower end of the Sylvian aqueduct. At each of the lateral 
 angles is an opening, called the foramen of Key and Retzius, 
 which connects the ventricle with the intermeningeal spaces 
 of the brain. Extending from the upper to the lower angle 
 is a median cleft that forms the dividing line between the 
 lateral halves of the floor. 
 
tliATE S. 
 
 The floor of the fourth ventricle and neighhoring structures : 1, Sylvian aqueduct . 
 2, corpora quadrigemina ; 3, strise acustiese ; 4, superior cerebellar peduncle ; 6, inferior 
 cerebellar peduncle ; 6, calamus scriptorius ; 7, fasciculus gracilis ; 8, fasciculus cunea- 
 tus ; 9, posterior median fissure ; 10, clava ; 11, tubereulum acusticum.— (Modified from 
 Spalteholz.) 
 
CHAPTER VI. 
 
 CONNECTIONS FORMED BY THE AFFERENT CR\NIAL 
 
 NERVES AND THE AFFERENT ROOTS OF THE MIXED 
 
 NERVES, AFTER REACHING THE CENTRAL 
 
 NERVOUS SYSTEM. 
 
 The Optic Nerve. — The fibers of the optic nerve — which 
 begins in the retina— end mainly in the external geniculate 
 body, though some extend farther back and end in the 
 superior quadrigeminal body and the posterior part of the 
 optic thalamus, these three structures serving as the optic 
 nuclei. Fibers from the nuclei, forming the optic radiation, 
 ascend through the posterior part of the internal capsule and 
 thence through the corona radiata to the visual area of the 
 occipital lobe. Mingled with theseafferent fibers are efferent 
 fibers which arise in the occipital cortex and end in the 
 nuclei of the oculo-motor, trochlear and abducent nerves, 
 forming a path through which rays of light may reflexly 
 cause movements of the eyeballs. 
 
 The Auditory Nerve. — The auditory nerve — which be- 
 gins in the internal ear — consists of a cochlear and a vestibu- 
 lar division, both of which enter the pons, the cochlear divi- 
 sion entering behind the restiform body, and the vestibular 
 division in front of it. 
 
 As the cochlear division enters it divides into two branches, 
 one of which ends in the accessory nucleus, and the other in 
 the tuberculum acusticvm. The fibers from the accessory 
 nucleus, running in the trapezium (which they form), cross 
 to the opposite side of the pons, some crossing directly and 
 the others by first winding outward round the restiform body 
 and then re-entering the tegmentum. They end in the 
 
 (65) 
 
66 CONNECTIONS OF THE AFFERENT CRANIA L NER VES. 
 
 trapezoidal nucleus and the superior olive of the opposite 
 side, from which new fibers, running upward in a bundle 
 called the lateral fillet, continue the path. The fibers from the 
 tuberculum acusticum run backward and outward across 
 the median raphe and across the opposite half of the floor of 
 the fourth ventricle — where they form the acoiostic striae — and 
 then turn upward and join the other fibers in the lateral 
 fillet. 
 
 The lateral fillet runs upward through the lateral part of 
 the pons and the isthmus to the final stations in the auditory 
 path. These are the internal geniculate body, the posterior 
 quadrigeminal body and a group of cells called the superior 
 nucleus of the fillet. Their fibers, forming the auditory radia- 
 tion, ascend through the posterior end of the internal capsule 
 and thence through the corona radiata, to the auditory area 
 in the temporal lobe. 
 
 As the vestibular division .enters the pons its fibers bifur- 
 cate and form ascending, and descending divisions. The 
 descending divisions extend to the lower end of the oblongata 
 and terminate in the nucleus posterior, a collection of gray 
 matter derived from the base of the posterior horn. Their 
 further relations are unknown. The ascending divisions join 
 the inferior cerebellar peduncle and pass to the cerebellum, 
 giving off in their course many collaterals to the nucleus of 
 Deiters and the nucleus of Bechterew, which lie near the lateral 
 angle of the ventricular floor. The flbers from the nucleus 
 of Deiters descend in the spinal cord and form the vestibulo- 
 spinal tract. They end in relation with the motor neurons 
 of the voluntary muscles. The fibers from the nucleus of 
 Bechterew take a descending course, but their destination is 
 unknown. 
 
 The Afferent Root of the Trifacial Nerve. — The 
 afferent root-fibers of the trifacial nerve arise from cells in the 
 Gasserian ganglion, which lies on the anterior surface of the 
 petrous bone. They enter the pons on its anterior surface 
 
THE AFFERENT ROOT OF THE FACIAL NERVE. 67 
 
 and bifurcate, forming ascending and descending divisions. 
 The ascending divisions end in the trifacial sensory nucleus, 
 situated in the pons. The descending divisions end mainly 
 in the nucleus gracilis, the nucleus cuneatus and the gelatinous 
 substance of Rolando, though some extend as low as the second 
 or third cervical segment of the spinal cord and end in the 
 posterior horn of the ppinal gray matter. Through fibers 
 arising in the two nuclei and the Rolandic substance, the 
 path is continued to the cerebrum by way of the fillet, and 
 to the cerebellum by way of the inferior peduncle. The 
 physiological relations of the fibers that descend in the cord 
 are undetermined. 
 
 The Afferent Root of the Facial Nerve. — The afferent 
 root-fibers of the facial nerve, which form the pars intermedia, 
 arise in the geniculate ganglion, situated in a canal in the 
 petrous bone. They enter the pons on its lateral surface and 
 run downward, terminating in the upper end of the sensory 
 nucleus, which also receives fibers from the ninth, and tenth 
 nerves. From the nucleus the path is continued by Abel's 
 which pass in the fillet and through the internal capsule to 
 the interior of the hemisphere and thence in part to the body- 
 sense area in the parietal lobe and in part to the gustatory 
 area in the temporal lobe. 
 
 The Afferent Roots of the Glosso-pharyngeal and 
 Pneumogastric Nerves. — The afferent root-fibers of the 
 glosso-pharyngeal nerve arise in the jugular and petrosal 
 ganglia, and those of the pneumogastric nerve arise in the 
 root-ganglion and the trunk., ganglion. These ganglia are 
 attached to their respective nerves and situated in the jugular 
 foramen. The fibers enter the oblongata between the olive 
 and the restiform body and bifurcate into ascending and de- 
 scending divisions. The ascending divisions terminate in 
 the column of gray matter that forms their nucleus. The 
 descending divisions, forming a bundle called tJie fasciculus 
 solitarius, run downward along the outer side of the sensory 
 
58 GONNECTIONS OF THE AFFERENT CRANIAL NER VES. 
 
 nucleus and terminate in the nucleus gracilis and the gela- 
 tinous substance of Rolando. Fibers arising in the various 
 nuclei continue the paths to the cerebrum and the cerebellum. 
 Some of the fibers in the glosso-pharyngeal nerve convey the 
 sense of taste. These form connections by which their im- 
 pulses reach the gustatory area in the temporal lobe. 
 
 Note. — For the central relations of the olfactory nerve, see 
 Part III., Chapter IV. 
 
Plate 6. 
 
 
 1 'H 
 ' 5 
 
 ^^H^^^v^ 
 
 'fis 
 
 
 -ifll 
 
 W^Br-M 
 
 fifl 
 
 fKfM 
 
 ■ 
 
 
 1 
 
 
 1 
 
 BMRVfB 
 
 ■ 
 
 
 9 
 
 
 ^1 
 
 H^BiJJ 
 
 9 
 
 
 mk 
 
 ^^^ '^m 
 
 1 
 
 The right side of the spinal cord with the spinal nerves attached. 
 {Modlfled from Spalteholia.) 
 
CHAPTER VII. 
 
 THE SPINAL CORD 
 
 The spinal cord extends through the vertebral canal from 
 the level of the base of the cranium to the body of the second 
 lumbar vertebra, and from its lower end the filum terminale 
 continues down to the coccyx. In the adult the cord proper 
 is about eighteen inches long and a half inch or less in diam- 
 eter and weighs nearly an ounce. Its surface presents the 
 anterior median fissure in front and the posterior median, 
 postero-intermediate and postero-lateral fissures behind, the 
 median fissures marking the lines of division between the 
 lateral halves of the cord. A minute channel, called the 
 central canal of the spinal cord, runs longitudinally through 
 the interior. 
 
 In each half of the cord is a continuous column of gray 
 matter commonly described as consisting of an anterior and 
 a posterior horn. The anterior horn projects a short dis- 
 tance ontward and forward. The posterior horn projects 
 outward and backward to the surface, ending at the postero- 
 lateral fissure. In this horn, near its termination, is a small 
 area in which the cells are mingled with fibers of the poster- 
 ior nerve-roots, and which is known as substantia gelatinosa. 
 The anterior horn contains the cells whose fibers form the 
 anterior roots of the spinal nerves, and throughout the entire 
 column are cells whose fibers form tracts in the cord. Of 
 these cells there are some whose fibers travel in the tracts of 
 their own side, others whose fibers cross to the tracts of the 
 opposite side, and still others whose fibers bifurcate and dis- 
 tribute a branch to each side. There are also Golgi cells of 
 
 (59) 
 
60 THE SPINAL COBD. 
 
 the second type, the fibers of which both run and end in the 
 gray matter. The columns of the two sides are united by 
 the anterior and posterior gray commissures. 
 
 The white matter in each half of the cord comprises the 
 anterior column, bounded by the anterior median fissure and 
 the anterior horn and nerve-root, the lateral column, bounded 
 by the anterior horn and nerve-root and the posterior horn, 
 and the posterior column, bounded by the posterior horn and 
 the posterior median fissure. The postero-intermediate fis- 
 sure and a fibrous septum divide the last-named column into 
 an inner part, called the postero-median column or the column 
 of GoU, and an outer part, called the postero-laleral column or 
 the column of Burdach. About the head of the anterior 
 horn is an area consisting of the adjoining parts of the an- 
 terior and lateral columns and often referred to as the antero- 
 lateral column. Its limits, however, are not very definitely 
 fixed. The two anteHor columns are connected with each 
 other by the white commissure. 
 
 On a functional basis the white matter of the cord is 
 divided into tracts, of three general classes. These are the 
 efferent tracts, the fibers of which are derived from the brain, 
 the association tracts, the fibers of which are derived from the 
 cord, and the afferent tracts, the fibers of which are derived in 
 part from the cord and in part from the ganglia of the pos- 
 terior nerve-roots. 
 
 The Efferent Tracts. 
 
 The Pyramidal Tracts. — The pyramidal fibers, which 
 connect the motor areas of the cerebrum with the motor 
 neurons of the cranial and spinal nerves, constitute the inter- 
 central paths through which the brain directs the movements 
 of the voluntary muscles. The fibers that make connections 
 with the cranial nerves cross to the opposite side in the 
 isthmus, pons and oblongata, at the levels of the various 
 motor nuclei in which they are destined to end. Of the 
 
TliM EMERENT TRACTS. 61 
 
 fibers that reach the spinal nerves, the greater part cross in 
 the pyramidal decussation and then descend in the posterior 
 part of the lateral columns of the cord, where they form the 
 crossed pyramidal tracts. The remaining fibers, which form 
 the direct pyramidal tracts, run in the anterior columns on the 
 same side as their origin, but pass through the white com- 
 missure to the opposite side before terminating. In their 
 course through the brain the pyramidal fibers distribute col- 
 laterals to the commissural fibers that connect the two hem- 
 ispheres of the cerebrum, and to the lenticular and caudate 
 nuclei. In the cord collaterals ar^ given off to the motor 
 neurons along the entire course of the pyramidal tracts. 
 
 The Rubro-spinal Tract. — The rubro-spinal tract, also 
 known as the pre-pyramidal tract and Monakow's bundle, 
 occupies a triangular area of the lateral column, in front of 
 the crossed pyramidal tract. Its fibers arise in the red 
 nucleus of the opposite side and end about the motor neurons 
 of the voluntary muscles. Together with the superior cere- 
 bellar peduncles, the rubro-spinal tracts constitute the paths 
 by which, as stated previously, each hemisphere of the cere- 
 bellum is connected with the motor neurons of the same side 
 of the cord. 
 
 The Vestibulo-spinal Tract. — This tract is situated in 
 front of the rubro-spinal tract and extends round the head of 
 the anterior horn. Its fibers arise in Deiter's nucleus (the 
 nucleus of the vestibular division of the auditory nerve) and 
 end in connection with the motor neurons of the voluntary 
 muscles. While its function is not definitely determined, it 
 may be supposed, in view of its anatomical connections, that 
 it forms a path through which vestibular impulses may 
 automatically affect the contraction of the muscles in the 
 maintenance of equilibrium. 
 
 The Sulco-marginal Tract. — This runs along the an- 
 terior median fissure in the anterior column. Its fibers 
 originate in the anterior quadrigeminal bodies and terminate 
 
62 THE SPINAL COBD. 
 
 in the anterior horns. Little is known of their physiology. 
 It is possible, however, that they form connections through 
 which visual impulses may in some way influence muscular 
 contraction. 
 
 The Anterior Marginal Tract. — This runs along the 
 periphery of the anterior column. Its fibers are thought to 
 arise in the nucleus fastigii of the cerebellum. Their desti- 
 nation is entirely unknown — likewise their physiology. 
 
 Helweg's Tract. — This tract is situated at the periphery, 
 near the front of the lateral column. Its fibers arise in the 
 nucleus of the inferior olive, but nothing is known of their 
 terminal relations or of their functions. 
 
 The Afferent Tracts. 
 
 As the central processes frgm the spinal ganglia enter the 
 cord, they bifurcate and form ascending and descending di- 
 visions. The descending divisions, which are short, pass to 
 the postero-lateral column and in this run downward in an 
 area known as the comma tract, so called from its resemblance 
 to the punctuation mark of the same name. They end in 
 the gray matter of the posterior horn. A few of the ascend- 
 ing divisions run upward a short distance in what is known 
 as the tract of Lissauer, which lies at the periphery beneath 
 the postero-lateral fissure. These, too, end in the posterior 
 horn. The remaining ascending fibers enter the posterior 
 columns. Of these there are some that end in the adjacent 
 gray matter of the cord, but the main fibers' continue up- 
 ward into the oblongata and end in the nuclei gracilis and 
 cuneatus, from which their subsequent connections are with 
 the cerebrum and the cerebellum. When the long fibers 
 first enter the posterior columns they travel in the postero- 
 lateral column or the tract of Burdach, but as they ascend they 
 are gradually crowded inward by fibers entering at higher 
 levels, until, at the upper end of the columns, the fibers from 
 the lumbar and sacral nerves are mainly in the postero- 
 median column or the tract of Goll. 
 
Plate 7. 
 I. 
 
 , t 
 
 UrosB-seotlon of the spinal cord : 1, posterior median fissure ; 2, central canal ; 3, sub- 
 stantia gelatinosa; 4, anterior median fissure ; 5, anterior white commissure ; 6, anterior 
 gray commissure ; 7, anterior horn ; 8, posterior horn ; 9, posterior commissure — (Modi- 
 iied from Spalteholz. ) 
 
THW'AFFERENT TRACTS. 63 
 
 
 Both the ascendir^'and the descending divisions give off 
 collaterals, which, after "tourses of varying length, enter the 
 gray matter and end about cells of the anterior and the pos- 
 terior horn. In part from the cells thus connected and in 
 part from cells about which the main fibers from the ganglia 
 end, arise other fibers which form the direct cerebellar tract 
 or the tract of Flechsig and the antero-lateral ascending tract or 
 the tract of Gowers. 
 
 The direct cerebellar tract arises from cells that lie at the 
 base of the posterior horn and form what is known as the 
 ' column of Clarke. This tract begins near the lower end of the 
 cord and runs upward along the margin of the lateral column, 
 directly in front of the posterior horn. On reaching the 
 oblongata it bends backward and enters the inferior cere- 
 bellar peduncle, of which it constitutes the greater part. Its 
 fibers, following the course of the peduncle, cross to the 
 opposite side and enter the cerebellum. They end mainly in 
 the middle lobe, but give off numerous collaterals to the 
 hemisphere of their own side, thereby connecting each hemi- 
 sphere with the afferent nerves of the same side of the cord. 
 
 The antero-lateral ascending tract is formed by fibers that 
 arise throughout the entire length of the cord. It runs 
 upward along the margin of the lateral column, in front of 
 the direct cerebellar tract, and appears on the lateral surface 
 of the oblongata. Its fibers continue upward through the 
 oblongata and pons into the isthmus, where they divide and 
 take different courses. Some unite with the fillet and ulti- 
 maltely reach the cortex of the cerebrum. The remainder 
 turn backward, enter the superior cerebellar peduncle and 
 pass to the middle lobe of the cerebellum, where they end. 
 
 There are other collaterals which, either directly or through 
 an intermediate neuron, make connections with the anterior 
 foot neurons and thus form the arcs for spinal reflexes. As 
 such collaterals arise along the entire course of the fibers, it 
 becomes possible for impulses entering the cord at one seg- 
 
64 ^SE SPINAL COM). 
 
 nient to cause reflexes in several segments either above or 
 
 below the level of their entrance. 
 Concerning the source of the impulses which the different 
 
 aSerent tracts conduct, there is some uncertainty. But 
 
 experimental study and pathological states have shown that 
 
 /the tracts of Goll, Burdach, Flechgig and Gowers, at least, 
 
 ( conduct impulses from the muscles, and that they are con- 
 
 \ sequently essential factors in the co-ordination of muscular 
 
 \iovements. That they also have other functions is believed 
 
 tu some extent, but not conclusively determined. 
 
 The Association Tracts. 
 
 The association tracts adjoin the gray matter in the antero- 
 lateral columns, being often referred to as the fundamental 
 or ground bundles of the cord. They consist of fibers which 
 arise in the gray matter of the cord, and which, after running 
 a distance of one or more segments in the white matter, 
 either up or down, again enter the gray matter and end about 
 other cells, thus connecting the different levels of the cord 
 and associating their activities. They conduct by a system 
 of relays, the impulses passing from one to another of the 
 neurons whose fibers form the tracts. Some of the ascending 
 or afferent association tracts are the principal paths for the 
 conduction of cutaneous impulses, and there is evidence that 
 the impulses which produce the different cutaneous sensa- 
 tions — pressure, pain and temperature — travel in different 
 parts of the tracts. There is further evidence that these 
 impulses, though conducted mainly on the side of the cord 
 that they enter, are conducted to some extent on the opposite 
 side — that is, that their conduction is bilateral. 
 
 Reflex Action. 
 
 Reflex action is that produced by sensory stimulation of 
 the efferent nerves. It occurs in glands and muscles, and in 
 the glands and the involuntary muscles is the regular mode 
 
heflex action. 65 
 
 of activitj'. In the voluntary muscles three types of reflexes 
 are recognized — namely, the simple reflex, affecting a single 
 muscle, and the co-ordinated and the convulsive reflex, each 
 affecting a number of muscles. Co-ordinated reflexes are 
 purposeful in character and are generally movements which 
 have become more or less habitual by training and experi- 
 ence, as walking, dancing and piano-playing. In such 
 movements the sensory impulses that arise from a given 
 stimulus and enter the cord through a given set of afferent 
 channels, find their way to a fairly constant set of efferent 
 channels and thus produce practically uniform effects on the 
 muscles. Convulsive reflexes are disorderly movements 
 made without purpose. They are possible under intense 
 sensory stimulation, with normal conditions prevailing, but 
 are not common. Their greatest frequency is in pathological 
 conditions in which the irritability of the nerve centers has 
 been greatly increased, as in strychnine poisoning, hydro- 
 phobia and uremia. In such conditions even a slight sen- 
 sory stimulus will often provoke spasms. In these cases, 
 owing to the heightened irritability of the central nervous 
 system, the sensory impulses radiate widely and affect many, 
 or even all, of the efferent neurons, instead of following the 
 usual, habitual path. From the physiological standpoint 
 convulsive reflexes are of interest as indicating an intimate 
 relation between all efferent and all afferent neurons. 
 
 The responses from reflex stimulation may be either in- 
 creased or decreased or entirely suppressed. "VS'ithin certain 
 limits the brain has an inhibitory influence on the reflex 
 activities of the centers for respiration, micturition and 
 defecation — that is, the activities of these centers may be 
 controlled to a certain extent by the will. The same in- 
 fluence may also be effective in restraining the reflexes of 
 the voluntary muscles. In tickling, for exaniple, an effort 
 of the will may suppress the usual convulsive movements 
 that the stimulus tends to produce. Whether this influence 
 5 
 
66 THE SPINAL COMB. 
 
 is exerted by the brain through a special set of fibers or by 
 some modification of the activity of the pyramidal fibers, is 
 an unsettled question. It is certain, however, that an in- 
 hibitory influence may emanate from the brain to all the 
 motor neurons of the voluntary muscles. A reflex may also 
 be partly or wholly suppressed by simultaneous sensory 
 stimulation in two places. Sneezing, for example, which 
 results from stimulation of the sensory nerves of the nasal 
 fossae, may often be checked by stimulating some of the 
 nerves of the skin; or a reflex movement in one limb may 
 be inhibited by simultaneous sensory stimulation of the 
 other limb. 
 
 On the other hand, simultaneous stimulation of the cord 
 from two sources will sometimes result in augmentation of a 
 reflex. If a strong voluntary movement is made simulta- 
 neously with a sensory stimulation, the response from the 
 latter is often increased. This result is explained by sup- 
 posing that the impulses originating in the brain and destined 
 for a definite set of neurons in the spinal cord, overflow, as 
 it were, from their customary channels and exert an influence 
 on the entire cord, with the effect of increasing its irritabil- 
 ity. This phenomenon, taken in connection with that in 
 which stimulation from two sources inhibits activity, evi- 
 dences a fact of importance on the physiological side- 
 namely, that the activity of any part of the cord may have 
 the effect either of increasing or decreasing the irritability of 
 the cord as a whole. It is also a further indication of the 
 intimate relation existing between all parts of the motor 
 apparatus. 
 
 Eefiex (responses are greatly affected by changes in the 
 irritability of the nerve-centers, being increased or decreased 
 by whatever increases or decreases this property. The 
 blood-supply has a marked influence in this respect, and so 
 also have many drugs, such as strychnine, chloroform and 
 opium. A pronounced increase in irritability is manifested 
 
THE KNEE-JERK. 67 
 
 in certain pathological states, being especially noticeable in 
 some of the diseases produced by germs. 
 
 The Knee-jerk. 
 
 This may be produced by a slight blow on the patellar 
 tendon, at a time when the quadriceps muscle is under ten- 
 sion. While it has the appearance of being a reflex move- 
 ment, it is not regarded as a reflex, in the true sense. It 
 is rather an evidence of the irritability of the quadriceps 
 muscle, by the contraction of which the movement is caused. 
 Since, however, the irritability of the muscle is dependent 
 upon adequate innervation, the movement is also an evi- 
 dence of the integrity of the afferent and efferent paths be- 
 tween the muscle and the spinal cord, as well as of the 
 condition at the nerve-centers. 
 
 The knee-jerk can be obtained in all normal individuals, 
 but varies even with the changing normal states, being abol- 
 ished during sleep and increased during mental excitation. 
 It is also affected by pathological conditions. For exa;mple, 
 if the afferent paths are functionally deficient, as in tabes 
 dorsalis, or the efferent paths, as in chronic anterior myelitis, 
 the blow on the tendon gives little or no response: or, on the 
 other hand, if lateral sclerosis is present, diminishing the 
 inhibitory influence ordinarily exercised by the brain, the 
 response is greatly intensified. Finally, it is increased or 
 decreased by an increase or decrease in the irritability of the 
 cord. It is therefore evident that the knee-jerk may be of 
 valuable service in diagnosis. 
 
 The Spinal Nerve-roots. 
 
 The anterior "roots, which arise from cells in the anterior 
 horn, leave the cord a short distance from the anterior med- 
 ian fissure, and form, at the surface, a vertical series of small 
 bundles, which extends the entire length of the cord. The 
 posterior roots, which consist of the central processes form 
 
68 THE SPINAL CORD. 
 
 the cells of the spinal ganglia, enter the cord at the postero- 
 lateral fissure. The roots of the upper cervical nerves are 
 short and horizontal, but below this they gradually increase 
 in length and run more and more obliquely downward, the 
 lowest descending perpendicularly from the end of the cord 
 and forming the cauda equina. The union of the two sets of 
 root-fibers forms the trunks of the spinal nerves. 
 
 The Spinal Membranes. 
 
 In all essential characteristics the membranes of the cord 
 are counterparts of the membranes of the brain, with which 
 they are continuous at the foramen magnum. The dura of 
 the cord, instead of forming the internal periosteum for the 
 vertebrae, is separated from them by the epidural space, 
 which contains areolar tissue and plexuses of veins. The 
 pia of the cord is somewhat less vascular than that of the 
 brain, and a lateral process of the pia forms the ligamentum 
 denticulatum, the outer edge of which is attached to the dura 
 between the openings for the spinal nerves. The arachnoid 
 presents no peculiarities of structure, but in the rear it forms 
 a median partition in the subarachnoid space. 
 
 The membranes are innervated by the recurrent branches 
 of the spinal nerves. 
 
PART III. 
 
 INNERVATION OF THE SKELETAL PARTS 
 OF THE BODY. 
 
CHAPTER I. 
 
 GENERAL DISTRIBUTION OF THE SPINAL NERVES. 
 
 The first cervical nerve emerges from the vertebral canal 
 between the occipital bone and the atlas; the coccygeal nerve, 
 through an opening at the lower extremity of the canal, and 
 all the other spinal nerves, through the inter-vertebral fora- 
 mina. Outside the vertebral column, each nerve gives off a 
 recurrent branch, which re-enters the vertebral canal, and then 
 divides into an anterior and a posterior division. 
 
 The Anterior Divisions. 
 
 In the cervical region the anterior divisions of the upper 
 four nerves form the cervical plexus, which innervates chiefly 
 the skin and muscles of the neck, and those of the lower four 
 nerves, 'uniting with a part of the first thoracic nerve, form 
 the brachial plexus, which innervates the arm and its related 
 muscles. 
 
 The anterior divisions of the first eleven thoracic nerves 
 form intercostal nerves, which course round the chest wall 
 between the internal and external intercostal muscles. The 
 upper six intercostal nerves, as they approach the anterior 
 ends of the external intercostal muscles, pass to the inner 
 surface of the internal intercostal muscles and then run for- 
 ward t3 the side of ,the sternum. Here they return to the 
 surface and end by becoming cutaneous. The lower five in- 
 tercostal nerves enter the abdominal wall and run forward as 
 far as the rectus muscle, here becoming superficial and being 
 finally distributed to the skin. The twelfth thoracic (sub- 
 costal) nerve runs along the lower border of the last rib and 
 
 (71) 
 
72 GENERAL DISTRIBUTION OF THE SPINAL NER VES. 
 
 thence among the abdominal muscles. The anterior thoracic 
 divisions, as a whole, innervate the intercostal, subcostal and 
 abdominal muscles, the levatores costarum, serrati posteriores 
 and triangularis sterni muscles, and the skin on the lateral 
 and anterior surfaces of the trunk. 
 
 The anterior divisions of the first three lumbar nerves, to- 
 gether with a part of the twelfth thoracic and a part of the 
 fourth lumbar nerve, enter the psoas muscle and there form 
 the lumbar plexus, the distribution of which is mainly in the 
 thigh, but to some extent in the genital organs. The re- 
 maining lumbar nerves unite with the first, second and third, 
 and a branch of the fourth, sacral nerves and form the sacral 
 plexus, which is distributed in the leg, gluteal region, genital 
 organs and perineum. Another branch of the fourth sacral 
 nerve and a branch of the fifth sacral nerve, form the coccy- 
 geal plexus, distributed in the perineum. 
 
 The Posterior Divisions. 
 
 The posterior divisions, which are smaller than the anter- 
 ior in all nerves except the first and second cervical, run 
 backward to th« dorsal tissues, where all but four — those of 
 the first cervical, fourth and fifth sacral and coccygeal nerves 
 — divide into an internal and an external branch. The in- 
 ternal branches — larger than the external branches from the 
 middle of the thorax upward, but smaller than these in the 
 region below — are distributed mainly to the skin, while the 
 external branches are distributed mainly to muscles. The 
 posterior divisions, as a whole, innervate the skin on the 
 back of the head, neck, trunk and gluteal region, and all the 
 posterior spinal muscles except the serrati posteriores and 
 levatores costarum and those connected with the upper limb. 
 
CHAPTER II. 
 
 GENERAL FUNCTIONS OF THE CRANIAL NERVES. 
 
 The First or Olfactory Nerve, the Second or Optic 
 Nerve and the Eighth or Auditory Nerve contain only 
 afferent fibers. The third, fourth, sixth, eleventh and 
 twelfth nerves contain only efferent fibers. But the fifth, 
 seventh, ninth and tenth nerves contain fibers of both classes. 
 
 The Third or Oculo-motor Nerve supplies efferent 
 (motor) fibers to both voluntary and involuntary muscles, 
 the latter innervating unstriated muscles of the eye. 
 
 The Fourth or Trochlear Nerve, the Sixth or Abdu- 
 cent Nerve, the Eleventh or Spinal Accessory Nerve 
 and the Twelfth or Hypoglossal Nerve are distributed 
 entirely to voluntary muscles. 
 
 The Fifth or Trifacial Nerve is the principal sensory 
 nerve of the face. It contains but few efferent fibers, and 
 these innervate onl}' voluntary muscles. 
 
 The Seventh or Facial Nerve and the Ninth or 
 Glossopharyngeal Nerve supply voluntary muscles with 
 motor fibers and blood-vessels with dilator fibers. They 
 also contain some secretory fibers. Among their afferent 
 fibers are those which mediate the sense of taste. 
 
 The Tenth, Vagus or Pneumogastric Nerve supplies 
 motor fibers to voluntary muscles, motor and inhibitory 
 fibers to viscera, dilator fibers to blood-vessels and secretory 
 fibers to glands. Among its afferent fibers are some that 
 perform special functions in the cardiac and respiratory 
 mechanisms. The pneumogastric nerve is an important 
 factor in a number of the so-called vital processes — digestion, 
 
 (73) 
 
74 GENERAL FUNCTIONS OF THE CRANIAL NERVES. 
 
 respiration, circulation and the action of the heart. It is 
 also widely distributed, as the characterizing term ' ' vagus ' ' 
 ("wandering") implies, some of its fibers innervating the 
 skin on the back of the ear, and others ramifying as far away 
 as the visceral organs of the abdomen. 
 
CHAPTER III. 
 
 INNERVATION OF THE EYE. 
 
 The nerves of the eye include the second, third, fourth 
 and sixth cranial nerves, the greater part of the first division 
 of the fifth nerve and some of the terminal branches of its 
 second division. 
 
 THE FIRST OR OPHTHALMIC DIVISION OF THE 
 FIFTH NERVE. 
 
 The first division of the fifth nerve, arising from the Gas- 
 serian ganglion, runs forward through the outer wall of the 
 cavernous sinus, under the fourth nerve, and passes through 
 the sphenoidal fissure into the orbit. Before entering the 
 orbit, it divides into three branches, lachrymal, frontal and 
 nasal. 
 
 The lachrymal nerve, entering the orbit at the outer angle 
 of the fissure, runs upward along the upper border of the ex- 
 ternal rectus muscle to the lachrymal gland, and thence to 
 the upper eyelid. It is distributed to the skin on the outer 
 part of the upper lid, to the outer part of the conjunctiva 
 and to the lachrymal gland. 
 
 The frontal nerve, running forward through the orbit on the 
 upper surface of the levator palpebrse muscle, gives off, mid- 
 way in its course, the supro-trochlear nerve. Then, becom- 
 ing the supra-orbital nerve, it continues forward and leaves 
 the orbit through the supra-orbital foramen, thence running 
 upward and being distributed over the forehead and front of 
 the scalp. The supra-trochlear nerve, running forward and 
 inward over the tendon of the superior oblique muscle, leaves 
 
 (75) 
 
76 INNERVATION OF THE EYE. 
 
 the orbit at its inner angle and becomes cutaneous between 
 the eyebrows, where it ends. It distributes branches to the 
 inner part of the conjunctiva and the upper eyelid. 
 
 The basal nerve, entering the orbit between the two divi- 
 sions of the third nerve, runs forward and inward a short dis- 
 tance and then passes upward through the anterior internal 
 orbital canal into the cranium. Here it runs forward on the 
 cribriform plate of the ethmoid bone, and then, turning 
 downward, descends through the nasal slit into the nasal 
 fossa, where it continues its downward course on th^ nasal 
 septum, ending in the skin near the end of the nose. Its 
 branches to the eye arise in the orbital fossa. These are the 
 short ciliary nerves, the long ciliary nerves and the infra- 
 trochlear nerve. 
 
 The short ciliary nerves, piercing the ciliary ganglion, spread 
 out on its peripheral side and are distributed to the coats of 
 the eyeball. 
 
 The long ciliary nerves, which arise behind the eyeball, join 
 the inferior group of the short ciliary nerves and pierce the 
 sclerotic. In the coats of the eyeball they continue forward 
 as far as the iris, innervating structures along their course. 
 
 The infra-trochlear nerve runs forward under the superior 
 oblique muscle and its tendon, to the inner angle of the eye, 
 distributing branches to the lachrymal sac, conjunctiva and 
 the skin on the inner part of the eyelid. 
 
 THE SECOND OR MAXILLARY DIVISION OF THE 
 FIFTH NERVE. 
 
 The second division of the fifth nerve, arising from the 
 Gasserian ganglion, leaves the cranium through the foramen 
 rotundum, crosses the spheno-maxillary fossa and passes 
 through the fissure of the same name into the orbit. Here it 
 continues forward, first in the infra-orbital groove and then 
 in the infra-orbital canal, from which it emerges through the 
 infra-orbital foramen into the tissues of the face. Here it 
 
f»LATE 8. 
 
 . Showing the nerves of the eye and the upper part of the mouth : 1, Supra-orbital 
 nerve ; 2, short ciliary nerves ; 3, optic nerve ; 4, upper division of the oculomotor 
 nerve ; 5, ciliary ganglion ; 6, lovfer division of the oculomotor nerve ; 7, trunk of 
 oculomotor nerve ; 8, trochlear nerve ; 9, ophthalmic division of trifacial nerve ; 
 10, Gasserian ganglion ; 11, trunk of the trifacial nerve ; 12, mandibular division of 
 the trifacial nerve ; 13, maxillary division of the trifacial nerve ; 14, spheno-palatine 
 gangUon ; 15, 16, 17, 18, palatine nerves ; 19, frontal nerve ; 20, supra-orbital nerve ; 
 21, Bupra-trochlear nerve ; 22, infra-orbital nerve ; 23, dental nerves ; 24, dental 
 plexus ; 25, 26, branches of dental nerves.— (Modified from Spalteholz. ) 
 
THE THIRD, FOURTH AND SIXTH NERVES. 7? 
 
 divides into superior labial, lateral nasal and inferior palpe- 
 bral branches, of which the last-named runs upward to the 
 conjunctiva and the lower lid. 
 
 THE THIRD OR OCULO-MOTOR NERVE. 
 
 The third nerve, arising from a nucleus in the floor of the 
 aqueduct and passing forward through the posterior longi- 
 tudinal bundle and the red nucleus, gains the oculo-motor 
 groove on the inner side of the crus cerebri, from which it 
 emerges -above the pons. From this point its course is for- 
 ward through the outer wall of the cavernous sinus to the 
 sphenoidal fissure, at the entrance of which it divides into a 
 superior and an inferior division. The superior division dis- 
 tributes lateral branches to the rectus superior muscle and 
 terminates in the levator palpebrse superioris. The inferior 
 division forms three branches : one to the internal rectus 
 muscle (derived from the sixth nucleus of the opposite side); 
 another to the inferior rectus muscle, and the third to the 
 inferior oblique. From this last branch springs a short offset 
 that ends in the ciliary ganglion and forms part of the 
 pupillo-constrictor path to the iris. 
 
 THE FOURTH OR TROCHLEAR NERVE. 
 
 The fourth nerve, which arises directly behind the third 
 nerve, crosses the median line and leaves the central axis on 
 the posterior surface of the pons. Winding outward over 
 the superior cerebellar peduncle and forward round the outer 
 side of the crus cerebri, it passes through the outer wall of 
 the cavernous sinus and the inner angle of the sphenoidal 
 fissure into the orbit. Here it runs over the levator palpe- 
 brse superioris muscle, to reach and supply the superior 
 oblique. 
 
 THEfSIXTH OR ABDUCENT NERVE 
 
 The sixth nerve, whose nucleus forms the eminentia teres 
 in the floor of the fourth ventricle, runs forward through the 
 
78 INNERVATION OF THE EYE. 
 
 ports and emerges at its lower border, a short distance from 
 the median line. Thence it runs forward through the cav- 
 ernous sinus and the sphenoidal fissure into the orbit, where 
 it is finally distributed to the external rectus muscle. 
 
 Note. — Fibers from the nucleus of the sixth nerve ascend 
 in the posterier longitudinal bundle and cross to the opposite 
 side. Here they join the third nerve and accompany it to the 
 internal rectus muscle. Thus the sixth nerve, which inner- 
 vates the external rectus of its own side, is in reality the 
 nerve which innervates the internal rectus of the opposite 
 side. 
 
 THE OPTIC NERVE. 
 
 The optic nerve, arising from cells of the retina, passes 
 back through the optic foramen to the optic groove on the 
 sphenoid bone. In this groove the fibers from the inner half 
 of each retina cross to the opposite side, forming what is 
 known as the optic chiasm,. Thence both the crossed and the 
 uncrossed fibers, forming i/te optic tracts, pass backward round 
 the outer side of the crura cerebri and end in the external 
 geniculate bodies, the superior quadrigeminal bodies and the 
 posterior part of the optic thalami. From these structures, 
 which constitute the optic nuclei, the path is continued, by 
 way of the optic radiation, to the visual area in the occipital 
 lobe of the cerebrum. In consequence of the decussation of 
 the inner fibers from each retina, each hemisphere of the 
 cerebrum receives visual impulses from the outer half of the 
 retina of its own side and from the inner half of the retina of 
 the opposite side. 
 
 Running in the optic chiasm and in the optic tracts is a 
 bundle of fibers which connects the inferior quadrigeminal 
 body and the internal geniculate body, both with each other 
 and with the corresponding structures of the opposite side. 
 It is known as Gudden's commissure. Its functional rela- 
 tions are with the auditory nerves. 
 
CHAPTER IV. 
 
 INNERVATION OF THE NASAL FOSSAE. 
 
 The nerves of the nasal fossae are the first cranial nerve 
 and branches of the first and second divisions of the fifth 
 nerve. 
 
 The first division of the fifth nerve contributes the nasal 
 nerve, already partly described. After entering the fossa it 
 divides into two branches: an internal branch, which supplies 
 the mucous membrane on the front part of the septum, and 
 an external branch, distributed to the front part of the lateral 
 wall. 
 
 The branches of the second division supplying the fossa 
 are the swperior nasal and the naso-palatine nerves, both of which 
 reach the fossa by piercing the spheno-palatine ganglion and 
 passing through the spheno-palatine foramen. In the fossa, 
 the naso-palatine nerve, running downward and forward 
 across the vomer and distributing branches to the septum on 
 its way, finally passes through the anterior palatine canal to 
 the roof of the mouth, where it unites, in a plexiform 
 manner, with its fellow nerve of the opposite side. The 
 superior nasal nerves — several small twigs — are distributed 
 to the mucous membrane that covers the upper and hind 
 portion of the superior and middle turbinated bones, and to 
 the corresponding region of the septum.' 
 
 Note. — The second division also supplies to the fossae a few 
 small branches that arise from the anterior superior dental 
 nerve and the anterior palatine nerve, which for the most 
 part are distributed in the mouth. 
 
 (79) 
 
80 INNERVATION OF THE NASAL FOSSAE. 
 
 THE OLFACTORY END-ORGAN AND THE FIRST OR 
 OLFACTORY NERVE. 
 
 In an area covering the upper third of the nasal septum 
 and the surface of the superior turbinated bone, are the cells 
 that constitute the olfactory end-organ. These cells are epi- 
 thelial-like in character and are mingled with columnar 
 epithelium that serves as support. At the peripheral or free 
 end of each cell are from six to eight fine, ciliary processes; 
 the proximal end is prolonged into a single, slender, non- 
 meduUated fiber. The proximal fibers from all the cells are 
 gathered into about twenty small bundles, which ascend 
 through the cribriform plate of the ethmoid bone and arbor- 
 ize about cells of the olfactory nucleus. This nucleus is con- 
 tained in the olfactory bulb, an oval body, two-fifths of an 
 inch in its long diameter, which lies on the cribriform plate 
 of the ethmoid and is covered above by the olfactory fissure. 
 From the nucleus fibers pass backward in the olfactory 
 groove of the sphenoid bone and the olfactory fissure of the 
 cerebrum, to the anterior perforated space, where they divide 
 into internal, middle and external divisions. From this 
 point the exact course of some of the fibers is imperfectly 
 traced. It is certain, however, that most of them finally 
 reach the olfactory area in the cortex of the cerebrum. It is 
 possible that some fibers decussate in the anterior com- 
 missure. 
 
CHAPTER V. 
 
 INNERVATION OF THE EXTERNAL PARTS OF THE HEAD. 
 
 TfiE external parts of the head, including the face, scalp 
 and external ear, receive their motor innervation from the 
 facial and trifacial nerves, and their sensory innervation from 
 the trifacial and pneumogastric nerves and the second and 
 third cervical nerves. 
 
 INNERVATION FROM THE FIRST AND SECOND DIVISIONS 
 OF THE TRIFACIAL NERVE, 
 
 From the first division of the trifacial nerve the branches 
 distributed in these parts are the following : 
 
 (1) The nasal nerve, which passes downward and supplies 
 the skip on the front and lower part of the nose. 
 
 (2) The infra-trochlear nerve, which passes downward and 
 supplies the skin on the front and upper part of the nose. 
 
 (3) The mpra-trochlear nerve, which passes inward and up- 
 ward and supplies the skin of the glabella. 
 
 (4) The supra-orbital nerve, which runs upward and sup- 
 plies the forehead and the anterior part of the scalp. 
 
 The branches from the second division are the tempero- 
 malar, superior labial and lateral nasal nerves. 
 
 2 he tempero-malar nerve, arising in the spheno-maxillary 
 fossa and passing through the fissure of the same name into 
 the orbit, there divides into a temporal and a malar branch. 
 The temporal branch, couraing upward along the outer wall 
 of the orbit and passing through the temporal canal of the 
 malar bone, turns upward under cover of the temporal mus- 
 cles and becomes superficial, being distributed in a narrow 
 strip of skin over the anterior part of the temple. The malar 
 branch, running forward and passing through the malar 
 6 (81) 
 
82 INNER VATION OF THE EXTERNAL PARTS OF HEAD. 
 
 canal of the malar bone, is distributed in the skin of the 
 malar region of the face. 
 
 Ihe superior labial and the lateral nasal nerves — ^terminal 
 branches of the second division — are distributed in the face, 
 in the regions corresponding to their names. 
 
 INNERVATION FROM THE THIRD OR MANDIBULAR 
 DIVISION OF THE TRIFACIAL NERVE. 
 
 The third division of the trifacial nerve contains both 
 afferent and efferent fibers. The afferent fibers arise in the 
 Gasserian ganglion ; the efferent fibers, from a column of 
 cells that begins in the pons and extends upward into the 
 isthmus. These latter fibers emerge from the anterior surface 
 of the pons and run forward to the foramen ovale, through 
 which, in company with the afferent fibers, they leave the 
 cranium. Outside the cranium the two. sets of fibers unite 
 and form a single trunk, which almost immediately divides 
 into an anterior and a pbsteribr division. 
 
 The trunk, before dividing, gives off the internal pterygoid 
 nerve, which supplies the muscle of the sanie name. 
 
 The Anterior Division forms the long buccal nerve, the 
 anterior and posterior deep temporal nerves and the masse- 
 teric nerve. • 
 
 The long buccal- nerve emerges between the heads of the 
 external pterygoid muscle, which it supplies through a few 
 small twigs, and then runs forward between the masseter and 
 buccinator muscles, distributing branches in the skin of the 
 cheek. 
 
 The anterior and the posterior deep temporal nerves, emerging 
 over the upper border of the external pterygoid muscle, run 
 upward and innervate the temporal muscles. 
 
 The masseteric nerve, also emerging over the upper border 
 of the external pterygoid muscle, turns downward and inner- 
 vates the masseter muscle. 
 
 The Posterior Division forms three main branches, the 
 
Plate 9. 
 
 Mandibular division of the. trifacial uerve : ], external pterygoid nerve; 2, buccinator 
 nerve ; 3, Gasserian ganglion ; 4, mandibular trunk ; 6, chorda tympani ; 6, aurionlo- 
 temporal nerve ; 7, branch to digastric muscle ; 8, facial nerve ; 9, inferior dental nerve ; 
 10, Ungual nerve ; 11, hypoglossal nerve ; 12, mylohyoid nerve ; 13, submaxillary gang- 
 lion ; 14, buccinator nerve.— (Modified from Spalteholz.) 
 
INNERVATION FROM THE CERVICAL NERVES. 83 
 
 lingual nerve (of the tongue), the auriculo-temporal nerve 
 and the inferior dental nerve. 
 
 The auriculo-temporal nerve ascends in front of the external 
 ear and divides into terminal branches in the skin of the 
 temple. It also distributes lateral branches to the tympa- 
 num, the external auditory meatus and the anterior border 
 of the pinna, and to the parotid gland and the skin of the 
 face. 
 
 The inferior dental nerve, which runs through the inferior 
 dental canal, leaves the canal at the mental foramen and 
 distributes its radiating terminal branches in the tissues of 
 the chin and the mucous membrane of the lower lip. 
 
 INNERVATION FROM THE CERVICAL NERVES. 
 
 The Great Auricular Nerve (2. 3. C), passing to the 
 hind border of the sterno-mastoid muscle and running upward 
 across it, divides into a facial, a mastoid and an auricular 
 branch. The facial branch is distributed to the skin in the 
 parotid and buccal regions of the face; the mastoid branch, 
 to the mastoid region of the scalp; and the auricular branch, 
 to the skin on the lower part of the back of the pinna. 
 
 The Small Occipital Nerve (2. C.) passes to the hind 
 border of the sterno-mastoid muscle and then upward to the 
 level of the mastoid process, where it divides into an auric- 
 ular, a mastoid and an occipital branch. The auricular 
 branch is distributed to the skin on the upper part of the 
 back of the pinna; and the mastoid and occipital branches 
 are distributed in the mastoid and occipital regions of the 
 scalp. 
 
 The Great Occipital Nerve, consisting of the internal 
 branch of the posterior primary division of the second cer- 
 vical nerve, is distributed in the occipital and parietal regions 
 of the scalp. 
 
 The Third Occipital Nerve, consisting of the internal 
 branch of the posterior primary division of the third cervicaj 
 nprvCj is distributed to the scalp in the mid-occipital regioij, 
 
84 INNERVATION OF THE EXTERNAL PARTS OF HEAD. 
 
 INNERVATION FROM THE PNEUMOGASTRIC NERVE. 
 The Nerve of Arnold, arising from the tenth nerve 
 at its root-ganghon and running back to the jugular fossa, 
 passes through Arnold's foramen into a canal in the petrous 
 bone. Here coursing at first backward and then downward, 
 it emerges from the petrous ' bone through the auricular 
 fissure and divides into two branches, one of which is dis- 
 tributed to the external auditory canal and to the skin on 
 the lower part of the back of the pinna. The remaining 
 branch joins the posterior auricular nerve. 
 
 INNERVATION FROM THE FACIAL NERVE. 
 
 The efferent portion of the facial nerve, arising from a 
 nucleus in the pons, pursues a circuitous route through the 
 substance of the pons and emerges at its lower border outside 
 the olive. Turning outward it passes through the internal 
 auditory meatus and enters the aqueductus Fallopii. "In this 
 it runs outward to the inner wall of the tympanum and then 
 backward a short distance in the substance of the wall. 
 Finally, making a sharp turn downward behind the posterior 
 wall of the tympanum, it passes through the stylo-mastoid 
 foramen to the under surface of the cranium and enters the 
 parotid gland, in which it divides into a tempero-facial and a 
 cervico-facial division. The tempero-facial division further 
 divides into temporal, malar and infra-orbital branches, and 
 the cervico-facial division, into buccal, supra-mandibular and 
 infra-mandibular branches, all of which, except the infra- 
 mandibular branch, are distributed to facial muscles, each 
 branch in the region corresponding to its name. 
 
 Prom the trunk of the nerve, before its division, arises the 
 posterior auricular nerve, which runs horizontally backward and 
 supplies the occipitalis muscle of the scalp. This nerve also 
 gives off lateral branches that pass upward and innervate the 
 piuscles of the external ear. 
 
CHAPTER VI. 
 
 INNERVATION OF THE MOUTH. 
 
 The mouth derives its innervation from the trifacial, facial, 
 glosso-pharyngeal and hypoglossal nerves. 
 
 INNERVATION FROM THE SECOND DIVISION OF THE 
 TRIFACIAL NERVE. 
 
 The second division of ' the trifacial nerve distributes 
 branches in the mouth, as follows : 
 
 (1) The posterior superior dental nerves (generally two in 
 number), arising in the spheno-maxillary fossa and descend- 
 ing on the hind surface of the maxilla, give off twigs to the 
 gums and buccal mucous membrane, and then, entering the 
 posterior dental canals, supply the molar teeth. 
 
 (2) The middle superior dental nerve, arising in the hind 
 part of the infra-orbital canal, descends in the outer wall of 
 the antrum and supplies the bicuspid teeth. 
 
 (3) The anterior superior dental nerve, arising in the front 
 pa^rt of the infra-orbital canal, descends in the wall of the 
 antrum and supplies the incisor teeth. 
 
 (4) The anterior palatine nerve, piercing the spheno-palatine 
 ganglion and descending through the posterior palatine canal, 
 runs forward on the hard palate, supplying the gums and the 
 roof of the mouth. 
 
 (5) The naso-palatine nerve, after reaching the roof of the 
 mouth, is distributed to the mucous membrane behind the 
 incisor teeth. 
 
 (6) A branch given off by the long buccal nerve is distributed 
 in the buccal mucous membrane. 
 
 (85) 
 
86 INNERVATION OF THE MOUTH. 
 
 INNERVATION FROM THE THIRD DIVISION OF THE 
 TRIFACIAL NERVE. 
 
 From the third division the branches distributed in the 
 mouth are the inferior dental nerve and the lingual nerve. 
 
 The inferior dental nerve supplies all the lower teeth and 
 distributes some fibers to the gums. 
 
 The lingual nerve runs downward and forward on the in- 
 ternal pterygoid muscle to the inner side of the jaw and then 
 forward between the mylohyoid and hyoglossus muscles to 
 the tip of the tongue. It supplies the anterior two-thirds of 
 the tongue and the adjacent parts of the gums. 
 
 INNERVATION FROM THE GLOSSO-PHARYNGEAL 
 NERVE. 
 
 The glosso-pharyngeal nerve contains both afferent and 
 efferent fibers. The afferent fibers arise from cells in the 
 jugular and petrosal ganglia, situated in the jugular fossa 
 and attached to the trunk of the nerve. The efferent fibers 
 arise from cells in the nucles ambiguus in the oblongata. 
 The two sets of fibers unite in the substance of the oblongata 
 and appear in a single bundle on its lateral surface, between 
 the restiform body and the lateral tract. From its super- 
 ficial origin the nerve runs outward and leaves the cranium 
 through the jugular foramen. Descending a short distance 
 between the internal carotid artery and the internal jugular 
 vein, it curves under the styloid process and passes to the 
 under surface of the hyoglossus muscle, where it divides into 
 terminal branches, of which those known as the lingual nerves 
 are distributed over the posterior third of the dorsum of the 
 tongue and the posterior half of its sides. These nerves con- 
 tain some of the fibers that convey sensations of taste. 
 
 INNERVATION FROM THE HYPOGLOSSAL NERVE. 
 
 The hypoglossal nerve, arising from' a long column of cells 
 in the oblongata and becoming superficial between the olive 
 
INNERVATION FROM THE FACIAL NERVE. 87 
 
 and the anterior pyramid, runs outward and leaves the 
 cranium through the anterior condylar foramen. From the 
 under surface of the cranium it runs at first downward, as 
 far as the lower border of the digastric muscle, and then 
 forward among the lingual muscles, as far as the tip of the 
 tongue, distributing branches to all the intrinsic tongue 
 muscles. It supplies the entire motor innervation of the 
 tongue. 
 
 INNERVATION FROM THE FACIAL NERVE. 
 The Chorda Tympani Nerve contains both efferent and 
 afferent fibers, its efferent fibers being derived from the facial 
 nucleus, and its afferent fibers from the geniculate ganglion, 
 which is attached to the facial nerve at its backward bend in 
 the petrous bone. Leaving the facial nerve at the lower end 
 of the Fallopian aqueduct, it enters the back part of the 
 tympanum, crosses the tympanic cavity and passes out of 
 the cranium through a canal at the inner side of the Glasser- 
 ian fissure, thence running downward and forward and join- 
 ing the lingual nerve, with which the afferent fibers continue 
 to the anterior two-thirds of the tongue, being distributed for 
 the most part to the taste-buds. The efferent fibers leave 
 the lingual nerve and end in sympathetic ganglia. 
 
CHAPTER VII. 
 
 INNERVATION OF THE INTERNAL PARTS OF THE EAR. 
 
 The nerves which contribute to the innervation of these 
 parts are the trifacial, facial, glossopharyngeal and auditory. 
 
 The trifacial nerve, through a small branch from its third 
 division, supplies the tensor tympani muscle; aiid the facial 
 nerve, through a branch arising in the aqueduct, supplies 
 the stapedius muscle. 
 
 The Tympanic Nerve, arising from the glossopharyngeal 
 nerve close under the base of the cranium, passes -through a 
 foramen that is situated between the carotid canal and the 
 jugular fossa, and thus reaches the tympanum. Here it 
 divides into branches and forms the tympanic plexus, from 
 which fibers are distributed to the mastoid cells, fenestra 
 rotunda, fenestra ovalis and Eustachian tube. 
 
 THE AUDITORY NERVE. 
 
 The auditory nerve consists of two divisions, the cochlear 
 division or the nerve of hearing, and the vestibular division 
 or the nerve of equilibrium. The cochlear division arises in 
 the spiral ganglion of the cochlea, and the vestibular division 
 in the vestibular ganglion of the vestibule. The two divi- 
 sions, running together through the auditory canal to the 
 lower border of the pons, here separate and pursue different 
 courses in reaching their nuclei, the vestibular division enter- 
 ing the pons in front of the restiform body, and the cochlear 
 division entering behind it. The cochlear division ends in 
 the accessory nucleus and the tuberculum acusticum, from 
 which the path is continued to the auditory area of the cere- 
 
 (88) 
 
THE A UBITOBT NERVE. 89 
 
 brum. The vestibular division ends partly in the nucleus 
 posterior and partly in the cerebellum^ the fibers to the cere- 
 bellum giving off collaterals to the nucleus of Deiters, whose 
 axis-cylinder processes descend in the vestibulo-spinal tract 
 and establish connection between the end-organ of equilib- 
 rium and the anterior horns of the cord»- j 
 
CHAPTER VIII. 
 
 INNERVATION OF THE SOFT PALATE AND TONSILS AND 
 THE PHARYNX AND LARYNX. 
 
 The nerves contributing to the innervation of these parts 
 are the trifacial, glosso-pharyngeal, pneumogastric and spinal 
 accessory. 
 
 COURSE OF THE PNEUMOGASTRIC AND SPINAL 
 ACCESSORY NERVES. 
 
 The Pneumogastric Nerve contains both afferent and 
 efferent fibers, the afferent fibers arising in the trunk-ganglion 
 and the root-ganglion, in the jugular foramen, and the effer- 
 ent fibers in the nucleus ambiguus, in the oblongata. Be- 
 coming superficial. on the side of the oblongata, between the 
 restiform body and the lateral tract, the two sets of fibers, at 
 first in from ten to fifteen fine strands, soon unite into a single 
 bundle and leave the cranium through the jugular foramen. 
 From the under surface of the cranium the trunk of the nerve 
 descends in the sheath with the internal carotid artery and 
 the internal jugular vein, and lower down with the same vein 
 and the common carotid artery. At the level of the clavicle 
 the right and left nerves take different courses. 
 
 The right nerve, entering the thorax between the sub- 
 clavian artery and the brachio-cephalic vein, bends backward 
 to the right side of the trachea and then descends to the pos- 
 terior surface of the root of the right lung, where it breaks up 
 and forms the posterior pulmonary plexus. Thence, as two 
 cords, it passes to the right side of the oesophagus, where it 
 again breaks up and joins with the left nerve in forming the 
 CBSophageal plexus. From here it runs along the posterior 
 
 (90) 
 
iNNMttVATtON FROM TBE TRIFACIAL NERVE. 91 
 
 surface of the oesophagus and passes through the cesophageal 
 opening of the diaphragm into the abdomen, being distributed 
 for the most part on the posterior surface of the stomach. 
 
 The left nerve, after forming a plexus on the posterior sur- 
 face of the root of the left lung, descends on the anterior 
 surface of the oesophagus and is distributed for the most part 
 on the anterior surface of the stomach. In other respects it 
 behaves like the right nerve. 
 
 The Spinal Accessory Nerve contains both cranial and 
 spinal fibers, the cranial fibers arising from the nucleus am- 
 biguus in the oblongata, and the spinal fibers from the upper 
 six or seven cervical segments of the cord. The cranial 
 fibers, emerging from the lateral surface of the oblongata, pass 
 to the jugular foramen and there unite with the pneumogas- 
 tric nerve, with which they are subsequently distributed. 
 The spinal fibers ascend on the side of the cord and pass 
 through the foramen magnum into the cranium. Here 
 joining the cranial fibers, they leave the cranium through 
 the jugular foramen and are then distributed, their destina- 
 tion being the sterno-mastoid and trapezius muscles. 
 
 INNERVATION FROM THE TRIFACIAL NERVE. 
 
 (1) The posterior palatine nerve, arising from the maxillary 
 division and piercing the spheno-palatine ganglion, descends 
 in an accessory palatine canal and distributes its fibers to the 
 soft palate, tonsil and uvula. 
 
 (2) The external 'palatine nerve, arising from the maxillary 
 division and piercing the spheno-palatine ganglion, descends 
 in another accessory palatine canal and distributes its fibers 
 to the soft palate and tonsil. 
 
 (3) The pharyngeal nerve, arising from the maxillary divi- 
 sion and piercing the spheno-palatine ganglion, runs back 
 through the pterygo-palatine canal and distributes fibers to 
 the naso-pharynx and the Eustachian tube. 
 
 (4) A small efferent nerve, arising from the mandibular divi- 
 
92 INNERVATION OF SOFl PALATE AND TONSILS. 
 
 sion and piercing the otic ganglion, innervates the tensor 
 palati muscle. 
 
 INNERVATION FROM THE GLOSSO-PHARYNGEAL NERVE. 
 
 (1) Two. or three tondUar nerves, ascending under the hyo- 
 glossus muscle to the tonsil, here from a plexus, called the 
 drculus tonsillaris, from which the fibers are distributed to 
 the tonsil and soft palate. 
 
 (2) Two or three pharyngeal merges, leaving the main nerve 
 below the petrous ganglion, descend over the internal carotid 
 artery to the back of the pharynx,., where they. join, with 
 nerves pf pneumogastric origin in lovmmg the "phoiryngecil 
 plexus.' ■ These nerves contain only afferent fibers. 
 
 INNERVATION FROM THE PNEUMOGASTRIC NERVE. 
 
 (ty.The pharyngeal nerve, leaving the main nerve at the 
 trunk-ganglion, runs downward to the back of the pharynx 
 and joins the ipharyngeal plexus. , It consists for the most 
 part of efferent, fibers derived from the spinal accessory nerve. 
 
 (2) The superior : laryngeal nerve, also leaving the, main 
 nerve at the trunk-ganglion, runs downward to the region of 
 the larynx and there divides into an internal and an external 
 branch. The internal branch, passing through the thyro- 
 hyoid membrane into the' larynx, is distributed to the mucous 
 membrane of the interior of thei larynx and pf the epiglottis. 
 The external branch, descending under the sterno-thyroid 
 muscle, ends in and innervates the crico-thyroid muscle. It 
 also supplies the inferior constrictor muscle of the pharynx 
 and distributes some fibers to the pharyngeal plexus and the 
 laryngeal mucous membrane. This nerve consists of afferent 
 fibers of pneumogastric origin and of efferent fibers derived 
 from the spinal accessory nerve. 
 
 (3) The inferior or recurrent laryngeal nerve, on the right 
 side of the body, leaves the main nerve at the level of the 
 lower border of the subclavian artery. Passing back under 
 
Plate 10. 
 
 12-^ 
 
 Deep nerves of the upper cervical region ; 1, glosso-pharyngeal nerve ; 2, braucli of 
 spinal accessory nerve ; 3, pharyngeal branch of vagus nerve ; 4, pharyngeal branch of 
 glosso-pharyngeal nerve ; 5, second cervical nerve ; 6, hypoglossal nerve ; 7, third cervi- 
 cal nerve ; 8, descendens hy poglossi ; 9, fourth cervical nerve ; 10, trunk of vagus nerve ; 
 11, ansa hypoglossi ; 12, phrenic nerve.— (Modified from Spalteholz.) 
 
DISTRIBUTION OF THE PHARYNGEAL PLEXUS. 93 
 
 this vessel, it runs upward and inward to the groove between 
 the trachea and oesophagus. The left recurrent nerve, leav- 
 ing the main nerve in front of the aortic arch, runs back 
 beneath it and enters the groove between the trachea and 
 oesophagus on the left side. In these grooves the two nerves 
 course upward under the inferior constrictor of the pharynx 
 and finally reach the inner surface of the ala of the thyroid 
 cartilage of the laryux. In this position each nerve forms its 
 terminal divisions, its branches being distributed to the 
 laryngeal mucous membrane and to all the laryngeal muscles 
 except the crico-thyroid. 
 
 DISTRIBUTION OF THE PHARYNGEAL PLEXUS. 
 
 The pharyngeal plexus is distributed to the muscles and 
 mucous membrane of the pharynx and to all the palatal 
 muscles except the tensor. 
 
 7 
 
CHAPTER IX. 
 
 INNERVATION OF THE CERVICAL REGION. 
 
 The innervation of the cervical region is derived to a slight 
 extent from some of the cranial nerves, but for the most part 
 from the upper four cervical nerves, by way of the cervical 
 plexus. 
 
 INNERVATION FROM CRANIAL NERVES. 
 
 (1) The mylohyoid nerve, springing from the inferior dental 
 nerve before it enters the inferior dental canal, runs forward 
 in the mylohyoid groove of the inferior maxilla and supplies 
 the mylohyoid muscle and the anterior belly of the digastric. 
 
 (2) The stylo-hyoid nerve, springing from the facial nerve 
 before its first division, supplies the stylo-hyoid muscle and 
 the posterior belly of the digastric. 
 
 (3) The infra-mandibular nerve, springing from the cervico- 
 facial nerve in the parotid gland, runs downward behind the 
 angle of the inferior maxilla and supplies the platysma, 
 being distributed on its inner surface. 
 
 (4) The spinal accessory nerve distributes a part of its spinal 
 fibers to the sterno-mastoid muscle. The remainder pass to 
 the under surface of the trapezius muscle and there join with 
 branches of the third and fourth cervical nerves in forming 
 the subtrapezial plexus, by which the trapezius is supplied. 
 
 INNERVATION FROM THE CERVICAL PLEXUS. 
 
 (1) Spinal fibers arising in the first and second cervical 
 nerves join the hypoglossal nerve close under the base of the 
 cranium. A few of these fibers run forward with the hypo- 
 glossal and supply the genio-hyoid and thyro-hyoid muscles. 
 
 (94) - 
 
Plate 11. 
 
 The cervical plexus : 1, posterior auricular nerve ; 2, great occipital nerve ; 3, 6, 
 great auricular nerve ; 4, small occipital nerve ; 5, third occipital nerve ; 7, branch 
 of spinal accessory nerve ; 8, superficial cervical nerve.— (Modified from Spalteholz.) 
 
INNERVATION FROM THE CERVICAL PLEXUS. 95 
 
 The greater part soon branch off as the descendens hypoghsd. 
 This runs down beneath the sterno-mastoid muscle to about 
 the level of the cricoid cartilage and there meets the ramus 
 cervicalis descendens, from the second and third cervical nerves, 
 the two descending branches forming the ansa hypoglossi. 
 From the descendens hypoglossi fibers are distributed to the 
 anterior belly of the omohyoid, and from the ansa hypoglossi, 
 to the sterno-hyoid, sterno-thyroid and the posterior belly of 
 the omohyoid. 
 
 (2) The Superficial Cervical Nerve (2. 3. C.) winds 
 round the hind border of the sterno-mastoid muscle and dis- 
 tributes cutaneous branches over the front of the neck from 
 the chin to the sternum. 
 
 (3) The Descending Cutaneous Nerve (3. 4. C. ), 
 running downward to the middle of the hind border of the 
 sterno-mastoid muscle, here becomes superficial and divides 
 into sternal, clavicular and acromial branches, each of which 
 is distributed to the skin in the region corresponding to its 
 name. 
 
 Note. — The posterior parts of the neck are innervated by 
 the posterior divisions of all the cervical nerves ; the recti 
 capitis and scaleni muscles, by the anterior divisions of the 
 upper four nerves. 
 
CHAPTER X. 
 
 INNERVATION OF THE SHOULDER AND ARM. 
 
 The shoulder and arm and their related muscles receive 
 their innervation by way of the brachial plexus, formed by 
 the lower four cervical and first thoracic nerves. 
 
 FORMATION OF THE BRACHIAL PLEXUS. 
 
 The cervical nerves that enter the plexus descend on the 
 anterior surface of the scalenus medius muscle. Here the 
 fifth and sixth nerves unite and form the upper trunk, the 
 seventh nerve becomes the middle trunk, and the first thoracic 
 nerve, passing upward over the first rib, unites with the 
 eighth cervical nerve, ■ the union of the two nerves forming 
 the lower trunk. The three trunks run downward and out- 
 ward to the subclavian triangle, where each divides into an 
 anterior and posterior division. The anterior division of the 
 lower trunk forms the inner cord; the anterior divisions of 
 the upper and middle trunks unite and form the outer cord ; 
 and the posterior divisions of the three trunks unite and form 
 the 'posterior cord. The three cords accompany the axillary 
 artery. Behind the pectoralis minor muscle the inner cord 
 lies at the inner side of the artery, the outer cord at its outer 
 side, and the posterior cord behind it. In these positions 
 each of the cords divides into its terminal divisions. 
 
 LATERAL BRANCHES OF THE PLEXUS. 
 
 The Rhomboid Nerve (5. C), leaving the main nerve 
 near the vertebral column, runs downward on the inner sur- 
 face of the levator scapulae muscle and along the inner 
 
 (96) 
 
Plate 12. 
 
 Showing the brachial plexus and its principal lateral branches : 1, fourth cervical 
 nerve ; 2, subscapular nerve ; 3, posterior thoracic nerve ; 4, suprascapular nerve ; 5, 
 anterior thoracic nerve ; 6, subclavian nerve ; 7, phrenic nerve ; 8, ansa hypoglossi ; 9, 
 descendens hypoglossi.— (Modified from Spaltebolz.) 
 
LATERAL BRANCHES OF THE PLEXUS. 97 
 
 border of the scapula and supplies both rhomboid muscles. 
 It also distributes. small brauches to the levator scapulae. 
 
 The Supra-scapular Nerve (5. C), arising from the 
 upper trunk and running downward and outward under the 
 trapezius muscle, passes through the suprascapular notch 
 and then divides into two branches, one of which suppUes 
 the supraspinatus muscle, and the other, winding round 
 through the great scapular notch, supplies the infraspinatus 
 muscle. 
 
 The Upper Subscapular Nerve (5. 6. C), arising from 
 the posterior cord, runs backward over the first rib and sup- 
 plies the upper part of the subscapular muscle. 
 
 The Lower Subscapular Nerve (5. 6. C), arising from 
 the posterior cord, runs backward and then downward and 
 supplies the lower part of the subscapular muscle and the 
 teres major. 
 
 The Long Subscapular Nerve (7. C), arising from the 
 posterior cord, descends on the posterior wall of the chest 
 and supplies the latissimus dorsi. 
 
 The Posterior Thoracic Nerve (5. 6. 7. C), formed 
 near the vertebral column, runs downward behind the plexus 
 and the axillary artery and thence downward on the outer 
 side of the chest wall, being finally distributed in the serratus 
 magnus muscle. 
 
 The External Anterior Thoracic Nerve (6. 7. C), 
 arising from the outer cord, descends on the front of the 
 chest wall and supplies the pectoralis major muscle. 
 
 The Internal Anterior Thoracic Nerve (8. C. 1. Th), 
 arising from the inner cord, descends on the front of the 
 chest wall and distributes branches both to the pectoralis 
 major and to the pectoralis minor. 
 
 The Subclavian Nerve (5. C), arising from the upper 
 trunk, descends in front of the subclavian artery and sup- 
 plies the subclavian muscle. 
 
98 INNERVATION OF THE SHOULDER AND ABM. 
 
 THE POSTERIOR CORD. 
 
 The posterior cord divides into the circumflex and musculo- 
 spiral nerves. 
 
 The Circumflex Nerve (5. 6. C.) passes back under the 
 lower border of the teres minor muscle and between the long 
 head of the triceps muscle and the neck of the humerus and 
 then divides into an anterior and a posterior branch. The 
 anterior branch winds round the humerus and supplies the 
 anterior part of the deltoid muscle. The posterior branch 
 supplies the teres minor muscle and the posterior part of the 
 deltoid. Both branches also distribute cutaneous fibers over 
 the upper and outer part of the arm. 
 
 The Musculo-spiral Nerve (6. 7. 8. C), winding out- 
 ward round the humerus and then coursing in the spiral 
 groove, reaches the outer side of the arm at a point between 
 the lower end of the brachialis muscle and the upper end of 
 the brachio-radialis. Here it divides into the posterior in- 
 terosseous and radial nerves. 
 
 The posterior interosseous nerve, running downward between 
 the brachialis and extensor carpi radialis longus muscles, 
 enters the supinator muscle and winds round the radius. 
 Emerging from the supinator it divides into several branches. 
 One of its branches runs downward as far as the wrist and 
 supplies the carpal joints ; the other branches are distributed 
 to the supinator and all the neighboring extensor muscles 
 except the extensor carpi radialis longus. 
 
 The radial nerve runs downward under the brachio-radialis 
 muscle to the lower third of the forearm, where it turns back- 
 ward under the tendon of the muscle and divides. Its 
 branches, continuing downward to the hand, are there dis- 
 tributed to the skin on the radial half of the dorsum and on 
 the back of the first two. and a half, digits as far down as the 
 last phalanges. 
 
 A few branches arise from the musculo-spiral nerve before 
 it divides. These are as follows : 
 
THE INNER CORD. 99 
 
 (1) Ihe internal cutaneous nerve, arising in the axilla, is dis- 
 tributed to a strip of skin on the inner side of the arm. 
 
 (2) The external cutaneous nerves, upper and lower, arising 
 farther down, are also distributed to the skin, the one over 
 the lower and outer part of the biceps, and the other on the 
 back of the forearm from the elbow to the wrist. 
 
 (3) Muscular branches, arising as the nerve reaches the 
 back of the humerus, supply, the three heads of the triceps 
 and the anconeus. 
 
 (4) Muscular branches arising just before the nerve divides, 
 supply the brachialis, the brachio-radialis and the extensor 
 carpi radialis longus. 
 
 THE OUTER CORD, 
 
 The outer cord divides into the musculo-cutaneous nerve 
 and the outer head of the median nerve. 
 
 The Musculo-cutaneous Nerve (5. 6. C), perforating 
 the coraco-brachialis muscle and then running downward and 
 outward between the brachialis and the biceps, comes to the 
 surface at the outer border of the biceps, above the bend 
 of the elbow. Thence it continues downward in a superficial 
 position into the forearm, where it divides into an anterior 
 and a posterior division. Before dividing it supplies the 
 muscles through and between which it passes. Its terminal 
 divisions are distributed to the skin on the radial side of the 
 forearm, from the elbow to the wrist. 
 
 THE INNER CORD. 
 
 The inner cord divides into the small internal cutaneous, 
 internal cutaneous and ulnar nerves and the inner head of 
 the median nerve. 
 
 The Small Internal Cutaneous Nerve (1. Th.) de- 
 scends on the inner side of the arm. to its middle and then 
 turns backward to supply a narrow strip of skin on the lower 
 third, of the arm. 
 
 The Internal Cutaneous Nerve (8. C. 1. Th.) descends 
 
100 INNEBVATIOJN OB THE SHOULDER AND ABM. 
 
 on the inner side of the arm to its lower third and then 
 divides into an anterior and a posterior division. These 
 continue downward and supply the skin on the ulnar half of 
 the forearm, from the elbow to the wrist. 
 
 The Ulnar Nerve (8. C. 1. Th.), descending first with 
 the brachial artery and then with the inferior profunda, 
 reaches the elbow. Here it passes between the external con- 
 dyle and the olecranon process^ and between the two heads of 
 the flexor carpi ulnaris muscle, to reach the under surface 
 of the flexor profundus, along which it courses to the lower 
 third of the forearm. Thence, in company with the ulnar 
 artery, it passes over the annular ligament into the palm, 
 where it divides into a deep and a superficial division. 
 
 The deep division is entirely distributed to these muscles: 
 the abductor poliicis, the inner head of the flexor brevis 
 poUicis, the flexor brevis minimi digiti, the opponens minimi 
 digiti, the abductor minimi digiti, the outer two lumbricales 
 and the interossei. 
 
 The superficial division is entirely cutaneous. It supplies 
 the palmar surface of the outer one and a half fingers and 
 the dorsum of their last phalanges.. 
 
 The ulnar nerve also gives off branches in its course 
 through the arm. These are as follows: 
 
 (1) A few small branches, arising near the elbow, supply 
 the elbow joint. 
 
 (2) Two muscular branches, arising below the elbow, sup- 
 ply the flexor carpi ulnaris and the outer part of the flexor 
 profundus. 
 
 (3) The palmar cutaneous nerve, arising near the middle of 
 the forearm and descending with the ulnar artery, supplies 
 the skin on the ulnar half of the palm. 
 
 (4) JTie dorsal cutaneous nerve, arising about two inches 
 above the wrist, turns backward under the flexor carpi ulnaris 
 muscle and then descends to the back of the hand. It sup- 
 plies the ulnar half of the dorsum of the hand, and the dor- 
 
Plate 13. 
 
 Nerves of the front of the forearm : 1, 5, median nerve ; 2, radial nerve ; 3, anter- 
 ior interosseous nerve ; 4, radial artery ; 6, ulnar nerve ; 7, ulnar artery— (Modified 
 from Spalteholz. ) 
 
TSE kEt)lAN NERtE. lOl 
 
 sum of the outer one and a half fingers, as far as their ungual 
 phalanges. 
 
 THE MEDIAN NERVE. 
 
 The median nerve (6. 7. 8. C. 1. Th. ) is formed by the 
 union of two short branches, one from the inner, and one 
 from the outer cord. It descends with the brachial artery to 
 the elbow and there passes between the heads of the pronator 
 teres muscle. Thence coursing through the middle of the 
 forearm, between the flexor sublimis and flexor profundus 
 muscles^ it runs under the annular ligament into the palm, 
 where it divides into an internal and an external division. 
 
 The internal division forms two branches, one to each of the 
 second and third finger clefts. Each branch divides into two 
 smaller digital branches, which course along the sides of the 
 contiguous fingers. They supply these fingers on their pal- 
 mar surface and the dorsum of their ungual phalanges. They 
 also supply the outer two lumbrical muscles. 
 
 The external division also forms two branches. One branch, 
 passing to the outer side of the thumb, supplies the abductor 
 pollicis, the outer head of the flexor brevis pollicis, the flexor 
 ossis metacarpi pollicis and the neighboring skin. The other 
 branch breaks up into collaterals that supply the skin on the 
 inner side of the thumb and the outer side of the index 
 finger. 
 
 In the arm the median nerve gives off branches as follows: 
 
 (1) A few branches, arising at the elbow, supply the pro- 
 nator teres, palmaris longus, flexor carpi radialis and flexor 
 sublimis digitorum muscles and the elbow joint. 
 
 (2) The anterior interosseous nerve, which arises a little be- 
 low the elbow and descends on the interosseous membrane, 
 distributes branches to the inner part of the flexor profundus 
 and the flexor longus pollicis, and then, passing under the 
 pronator quadratus, supplies that muscle and the wrist joint. 
 
 (3) The 'palmar cutaneous nerve, arising above the annular 
 ligament and descending to the hand, is distributed to the 
 skin on the radial half of the palm. 
 
CHAPTER XI. 
 
 INNERVATION OF THE HIP AND LEG. 
 
 The innervation of these parts is derived from the five 
 lumbar nerves and the first three sacral nerves, by way of 
 the lumbar and sacral plexuses. 
 
 INNERVATION THROUGH THE LUMBAR PLEXUS. 
 
 The Ilio-inguinal Nerve (1. L. ), running outward 
 parallel with the iliac crest and passing through the inguinal 
 canal to the external abdominal ring, here divides into sev- 
 eral branches, some of which supply the skin on the upper 
 and inner part of the thigh. 
 
 The Ilio-hypogastric Nerve (1. L..), running parallel 
 with the iliac crest, divides into two branches, one of which, 
 the iliac nenve, supplies the skin between the iliac crest and 
 the great trochanter. 
 
 The Genito-crural Nerve (1. 2. L.) descends over the 
 anterior surface of the psoas muscle until near the bifurca- 
 tion of the common iliac artery, where it divides into a gen- 
 ital and a crural branch. The crural branch, passing under 
 the inguinal ligament, supplies the skin on the front and 
 upper part of the thigh. 
 
 The External Cutaneous Nerve (2. 3. L.), piercing the 
 psoas muscle and passing over the iliacus to a point below 
 the anterior superior iliac spine, runs thence under the in- 
 guinal ligament and supplies the skin on the outer side of the 
 thigh. 
 
 The Anterior Crural Nerve (2. 3. 4. L.), descending 
 along the outer border of the psoas muscle, distributes lateral 
 
 (102) 
 
Plate 14. 
 
 Nerves of the back of the thigh ; 1, superior gluteal nerve ; 2, inferior gluteal 
 nerve ; S, sciatic nerve ; 4, popliteal jierv«; 5, peroneal nerve.— (Modified from- 
 Spalteholz ) 
 
 8 
 
INNERVATION THROUGH THE SACRAL PLEXUS. l03 
 
 branches to the iliacus muscle, and then, passing under the 
 inguinal ligament into the thigh, divides into terminal 
 branches, as follows : 
 
 (1) Muscular branches, arising soon after the nerve enters 
 the thigh, supply the rectus femoris, the vastus internus, the 
 vastus externus, the vastus intermedius and the pectineus. 
 
 (2) The middle cutaneous nerve, consisting of two branches, 
 supplies the skin on the front of the thigh. One of its 
 branches also perforates and supplies the sartorius muscle. 
 
 (3) The internal cutaneous nerve descends with the femoral 
 artery and supplies the skin on the inner side of the thigh. 
 
 (4) The internal saphenous nerve, descending through Hun- 
 ter's canal and then with the internal saphenous vein, sup- 
 plies the skin on the inner side of the leg below the knee, and 
 on the inner side of the foot as far as the ball of the great toe. 
 
 The Obturator Nerve (2. 3. 4. L.) follows the inner 
 border of the psoas muscle to the pelvic brim and then passes 
 to the obturator foramen, through which it leaves the pelvis 
 in two divisions. It supplies the adductor magnus, the ad- 
 ductor longus, the adductor br'evis, the adductor gracilis and 
 the obturator externus, and distributes some branches to the 
 hip joint. 
 
 The Patellar Plexus, formed by branches of the ex- 
 ternal, middle and internal cutaneous nerves, is distributed 
 to the skin about the patella. 
 
 The Subsartorial Plexus, formed by branches of the 
 internal cutaneous, internal saphenous and obturator nerves, 
 is situated beneath the sartorius muscle in the lower third 
 of the thigh. Its fibers are distributed to surrounding 
 structures^ 
 
 INNERVATION THROUGH THE SACRAL PLEXUS. 
 
 The Superior Gluteal Nerve (4. 5. L. 1. S.), leaving 
 the pelvis through the great sacro-sciatic foramen and pass- 
 ing above the pyriformis muscle, runs outward and upward 
 
104 INNERVATION OF THE HIP AND LEG. 
 
 and supplies the gluteus medius, gluteus minimus and ten- 
 sor vaginae femoris muscles. 
 
 The Inferior Gluteal Nerve (4. 5. L. 1. S.), leaving 
 the pelvis through the great sacro-sciatic foramen but passing 
 under the pyriformis muscle, runs outward and downward 
 and supplies the gluteus maximus muscle. 
 
 Note. — Closely related to the gluteal nerves in origin are 
 three small nerves that supply the quadratus femoris, gemel- 
 lus superior, obturator internus and pji^riformis muscles. 
 
 The Perforating Cutaneous Nerve, perforating the 
 great sacro-sciatic ligament, is distributed to the skin over 
 the lower and inner part of the gluteus maximus muscle. 
 
 The Small Sciatic Nerve (1. 2. 3. S.), entering the 
 thigh under the pyriformis muscle, is distributed to the skin 
 on the lower part of the buttock, and on the back of the thigh 
 as far down as the knee. The long pudendal nerve, a branch 
 of the small sciatic, is distributed to the skin on the upper 
 and inner part of the thigh. 
 
 The Great Sciatic Nerve (4. 5. L. 1. 2. 3. S.), entering 
 the thigh under the pyriformis* muscle and descending on the 
 adductor magnus muscle for a variable distance below the 
 middle of the thigh, divides into the popliteal and peroneal 
 nerves. Before dividing it distributes lateral branches to the 
 biceps flexor cruris, semimembranosus, semitendinosus and 
 adductor magnus muscles. 
 
 The Popliteal Nerve (4. 6. L. 1. S.), which extends 
 to the lower end of the popliteal space, supplies the soleus, 
 gastrocnemius, popliteus and plantaris muscles and the knee- 
 and tibio-fibular joints. It also gives off a cutaneous 
 branch, the tibial communicating nerve, which descends on the 
 back of the calf and joins the fibular communicating nerve, a 
 branch of the peroneal, the union of the two branches forming 
 the short saphenous nerve, which accompanies the vein of the 
 same name and passes along the side of the heel and foot to 
 the little toe, distributing branches to the skin in the region 
 through which it travels. 
 
Plate 15. 
 
 Deepnervesof thebackof theleg: 1, sciatic nerve; 2, popliteal nerve ; S, peroneal 
 nerve ; i, posterior tibis.! nprve.— (ModiSed ftom Spalteholz,) 
 
INNERVATION THROUGH THE SACRAL PLEXUS. 105 
 
 The Posterior Tibial Nerve (4. 5. L. 1. 2. S. )— a con- 
 tinuation of the popliteal nerve — descends through the calf 
 to a point between the os calcis and the internal malleolus 
 and then divides into the internal and external plantar nerves. 
 Before forming its terminal divisions it gives off lateral 
 branches to the soleus, tibialis posterior, flexor longus hal- 
 lucis and flexor longus digitorum muscles, and a cutaneous 
 branch, the calcaneo-plcmtar nerve, that supplies the inner and 
 under surface of the heel. 
 
 The Internal Plantar Nerve distributes branches as fol- 
 lows : muscular branches to the adductor hallucis, flexor 
 brevis hallucis, flexor brevis digitorum and the inner two 
 lumbricales ; articular branches to some of the joints of the 
 foot, and cutaneous branches to the inner part of the sole, 
 the under surface of the first three and a half toes and the 
 dorsum of their ungual phalanges. 
 
 The External Plantar Nerve distributes branches as 
 follows :' muscular branches to the flexor accessorius, flexor 
 brevis minimi digiti, adductor obliquus hallucis, adductor 
 transversus hallucis, interossei and the outer two lumbricales ; 
 articular branches to some of the joints of the foot, and 
 cutaneous branches to the outer part of the sole, the under 
 surface of the outer one and a half toes and the dorsum of 
 their ungual phalanges. 
 
 The Peroneal Nerve (4. 6. L. 1. 2. S.) runs downward 
 and outward to the upper end of the peroneus longus muscle 
 and there divides into the musculo-cutaneous and anterior 
 tibial nerves. Before dividing it gives off articular branches 
 to the knee joint, and a cutaneous branch, the lateral cutaneous 
 nerve, which supplies the upper two-thirds of the outer side 
 of the leg. 
 
 The Musculo-cutaneous Nerve descends under the 
 peroneal muscles and distributes branches to the peroneus 
 longus and the peroneus brevis. Near the lower fourth of 
 the leg it becomes superficial and divides into terminal 
 
106 INNERVATION OF THE HIP AND LEG. 
 
 branches, which are distributed to the skin on the lower 
 fourth of the leg and the dorsum of the foot. 
 
 The Anterior Tibial Nerve descends on the interosseus 
 membrane with the anterior tibial artery and passes under 
 the annular ligament, from which it emerges in an internal 
 and an external division. In the leg it distributes branches 
 fo the tibialis anterior, extensor longus digitorum, extensor 
 proprius hallucis and peroneus tertius muscles and to the 
 ankle joint. The internal division runs to the cleft between 
 the first two toes and distributes digital branches to the skin 
 on their contiguous surfaces. The external division supplies 
 the extensor brevis digitorum muscle. 
 
CHAPTER XII. 
 
 INNERVATION OF THE EXTERNAL GENITAL ORGANS 
 AND THE PERINEUM. 
 
 These parts derive their innervation from the first and 
 second lumbar nerves, and from the sacral and coccygeal 
 nerves, by way of the sacral and coccygeal plexuses. 
 
 The Ilio-inguinal Nerve (1. L.), as it leaves the ex- 
 ternal abdominal ring, gives off branches that are distributed 
 to either the scrotum or the labium ma jus, according to sex. 
 
 The Genito-crural Nerve (1. 2. L.), through its genital 
 branch, supplies the cremaeter muscle. In the female it 
 accompanies and supplies the round ligament. 
 
 The Inferior Pudendal Nerve (1. 2. 3. S.), a branch of 
 the small sciatic, emerging under the gluteus maximus 
 muscle and winding inward round the thigh, contributes 
 further innervation to either the scrotum or the labium 
 majus. 
 
 The Pudic Nerve (2. 3. 4. S. ), leaving the pelvis through 
 the great sacro-sciatic foramen and running forward in the 
 outer wall of the ischio-rectal fossa, divides into the perineal 
 nerve and the dorsal nerve of the penis. 
 
 The 'perineal nerve divides into a deep and a superficial 
 division. The deep division is distributed to the ischio- 
 cavernosus, bulbo-cavernosus, transversus perinei, levator 
 ani and sphincter ani externus muscles, and to the corpus 
 spongiosum and the mucous membrane of the urethra. The 
 superficial division divides into an internal and an external 
 branch. The internal branch pierces the transverse perineal 
 muscle and then runs forward on the inner side of the peri- 
 
 (107) 
 
108 THE EXTERNAL GENITAL ORGANS. 
 
 neal vessels. The external branch crosses the transverse 
 muscle and runs forward on the outer side of the perineal 
 vessels. Both branches are distributed to either the scrotum 
 or the labium majus and to the skin of the perineum. 
 
 The dorsal nerve of the penis, running forward between the 
 layers of the triangular ligament, finally pierces the outer 
 layer and continues forward along the dorsum of the penis 
 as far as the glans. It supplies the corpus cavernosum and 
 the constrictor urethrae muscle. The corresponding nerve 
 in the female is distributed to the clitoris. 
 
 The Coccygeal Plexus, formed by the coccygeal nerve 
 and branches of the fourth and fifth sacral nerves, is dis- 
 tributed to the levator ani, coccygeus and sphincter ani ex- 
 ternus muscles and to the skin about the anus. 
 
CHAPTER XIII. 
 
 INNERVATION OF THE RESPIRATORY MECHANISMS. 
 
 The Inspiratory Nerves and Muscles. 
 
 The inspiratory or active phase of respiration involves the 
 activity of a number of motor nerves, among the most im- 
 portant of which is the phrenic, supplying the diaphragm. 
 
 The Phrenic Nerve, arising from the fourth and fifth 
 cervical segments of the cord, descends over the anterior 
 scalenus muscle and beneath the supracapsular artery and 
 then passes behind the subclavian vein into the thorax. 
 From this point the right nerve descends along the outer 
 side of the pericardium to the front of the right lung and 
 thence between the lung and thoracic wall to the diaphragm. 
 The left nerve crosses the aortic arch and the pericardium to 
 the front of the left lung, whence its course is similar to that 
 of the right nerve. Both nerves pierce the diaphragm and 
 are distributed on its lower surface. 
 
 The diaphragm also receives a few branches from the lower 
 intercostal nerves, but they are of far less importance than 
 the phrenics. 
 
 The other motor nerves concerned in inspiration, together 
 with the inspiratory muscles which they innervate, are the 
 following: The intercostal nerves, supplying the external inter- 
 costal muscles, the intercartilaginous portion of the internal 
 intercostals and the serratus posterior; the cervical plexvs, 
 supplying the anterior, medius and posterior scaleni; the 
 brachial plexus, supplying the pectoralis minor; the spinal 
 accessory nerve, supplying the sterno-cleido-mastoid; the facial 
 nerve, supplying the elevators of the wings of the anterior 
 
 ( 109 ) 
 
110 THE BESPIRATOBY MECHANISMS. 
 
 nares; and the 'pnmm.ogaslric nerve, supplying the posterior 
 crico-arytenoid muscle of the larynx. 
 
 Action of the Inspiratory Muscles. 
 
 Contraction of the diaphragm causes its convex upper sur- 
 face — which, when the muscle is at rest, invades the thorax 
 — to become flattened and the muscle to descend, the effect of 
 which on the thoracic side is enlargement of the chest in its 
 vertical diameter. On the abdominal side it produces an in- 
 crease of pressure, which is transmitted through the viscera 
 and causes protrusion of the abdominal wall, as is evidenced 
 in what is known as the abdominal or diaphragmatic type of 
 breathing. Contraction of the muscles about the chest and 
 in the neck elevates the ribs and enlarges the chest in cir- 
 cumference. With the expansion of the chest, due to the 
 contraction of the inspiratory muscles, the air enters the 
 lungs under the pressure of the outside atmosphere, and this 
 constitutes the inspiratory phase of respiration. 
 
 Contraction of the elevators of the wings of the nose dilates 
 the anterior nares, and contraction of the posterior crico- 
 arytenoid muscle dilates the glottis, thus in both cases mak- 
 ing freer passage for the entering current of air. 
 
 In the usual inspirations, such as are made without con- 
 scious effort, only the diaghragm and the levatores costarum 
 are active, but in labored or difficult breathing any or all of 
 the other inspiratory muscles may come into play, depending 
 upon the force and amplitude of the inspiratory movements. 
 
 The Expiratory Nerves and Muscles. 
 
 The ordinary type of expiration, such as occurs in normal 
 breathing, is a purely passive process, the lungs, after being 
 expanded by an inspiration, collapsing under such physical 
 influences as their own elasticity and the weight of the chest 
 walls. Expiration, however, occasionally becomes an active 
 process, and then involves coptraction of the intprosseous 
 
THE REPIRATOBY CENTER 111 
 
 portion of the internal intercostal muscles and of the trian- 
 gularis sterni, serratus posterior inferior and abdominal mus- 
 cles, all supplied by the intercostal nerves, and contraction of 
 the quadratus lumborum muscle, supplied by the lumbar 
 nerves. 
 
 Action of the Expiratory Muscles. 
 
 Contraction of the abdominal muscles causes pressure on 
 the abdominal viscera. If the glottis is simultaneously di- 
 lated, allowing the air to escape from the lungs, the pres- 
 sure is exerted upon the diaphragm, pushing it upward into 
 the thorax and thus diminishing the size of the chest cavity. 
 If, however, the glottis is kept closed, retaining the air in 
 the lungs, the diaphragm becomes immovable, and the pres- 
 sure is then exerted upon the pelvic viscera — an effect that 
 has an important bearing upon all straining movements in 
 which the action of the pelvic organs is involved. 
 
 Contraction of the other expiratory muscles pulls the ribs 
 downward, the effect of which on the thorax is to further 
 diminish its size by reducing its lateral and antero-posterior 
 diameters. 
 
 Functions and Properties of the Respiratory Center. 
 
 Both the inspiratory and the expiratory muscles belong in 
 the skeletal group and are under voluntary control, but in 
 respiration their movements are directed and co-ordinated by 
 the respiratory center in the medulla. This center comprises 
 two functionally distinct groups of cells, one of which, acting 
 in inspiration, may be termed the inspiratory center, and the 
 other, acting in expiration, the expiratory center. 
 
 Expiration being normally passive and inspiration always 
 active, it is evident that the inspiratory center exerts the 
 greater influence in respiratory control. This center is 
 rhythmical in its action and also possesses the peculiar prop- 
 erty of being automatic. Its automatic activity is the result 
 of chemical changes that take place in its cells, due to the 
 
1 1 2 TSE RESPIMA TOR Y MECHANISMS. 
 
 presence of carbon dioxid in its blood-supply. The rhythm of 
 its action is maintained by afferent fibers contained in the 
 pneumogastric nerves and distributed to the air-Vesicles of 
 the lungs. When the lungs are expanded by an inspiration, 
 these fibers are mechanically stimulated by the expansion and 
 their impulses have an inhibitory effect on the inspiratory 
 center, cutting short the inspiration and causing expiration, 
 after which the center again discharges, under the influence 
 of its normal chemical stimulus. These fibers are the chief 
 factors in maintaining the normal rate of respiration. 
 
 The pneumogastric nerves supply the lungs with another 
 set of afferent fibers, which have an accelerating effect on the 
 inspiratory center. Concerning the extent to which these 
 fibers are involved in ordinary respiration and the circum- 
 stances under which they are stimulated, there is no uni- 
 versal agreement. The most generally accepted belief is that 
 they are stimulated by collapse of the lungs at the end of ex- 
 piration and thus hasten the resumption of the inspiratory 
 . movements. There is no evidence, however, that they have 
 any important part in the maintenance of the respiratory rate. 
 
 TTie expiratory center is active only when expiration becomes 
 an active process. This center, unlike the inspiratory center, 
 is not automatic, but is normally stimulated either by im- 
 pulses received through various afferent paths or by impulses 
 received through intercentral fibers from the cerebral cortex. 
 
 Modifications of the Respiratory Movements. 
 
 The activity of the respiratory center, and consequently 
 the respiratory movements, may be modified reflexly in 
 different ways, by stimulation of sensory fibers in various 
 parts of the body. Strong stimulation of the cutaneous 
 fibers may produce either an increase or a decrease in both 
 the rate and amplitude, or temporarily inhibit all respiratory 
 movements. Complete inhibition may also be obtained by 
 stimulation of the splanchnic nerves or by stimulation of the 
 
MODIFICATIONS OF BESPIRATOBY MOVEMENTS. 113 
 
 glosso-pharyngeal fibers supplying tiie mucous membrane of 
 the pharynx. Certain forms of stimuli acting on the tri- 
 facial fibers that supply the mucous membrane of the nose, 
 will so excite the expiratory center as to produce the type of 
 expiration that occurs in sneezing. When the pneumogastric 
 fibers supplying the interior of the larynx, the trachea or the 
 bronchi are stimulated, as by mucous or foreign bodies, the 
 effect is transmitted to the expiratory center and the forced 
 expirations of coughing ensue. Stimulation of the pneumo- 
 gastric fibers supplying the lining membrane of the stomach, 
 may either excite the expiratory movements of coughing or 
 cause the sudden and involuntary contractions of the dia- 
 phragm that occur in the inspiratory movements of hic- 
 coughing. 
 
 Respiration may also be affected by emotional states, 
 through the efferent paths extending from the cortex of the 
 cerebrum to the respiratory center of the medulla. Emotions 
 may either increase or decrease both phases of respiration, or 
 cause the inspiratory movements of sighing and sobbing and 
 the expiratory movements of laughing. 
 
 Finally, respiratory movements may be increased, de- 
 creased or entirely suspended by voluntary control. But in 
 complete voluntary suspension of respiration the accumula- 
 tion of carbon dioxid in the blood so increases the irritability 
 of the respiratory center that it eventually overcomes the 
 voluntary inhibition and respiration is resumed. Whether 
 the voluntary control of respiration is effected entirely 
 through the pyramidal fibers that make connections with the 
 efferent neurons of the respiratory muscles, or to some extent 
 through the intercentral fibers that connect the cerebral cor- 
 tex with the respiratory center, is not known. 
 
 Note. — For the efferent innervation of the bronchi, see 
 page 141. 
 
PART IV. 
 
 THE SYMPATHETIC NERVES AND THE INNER- 
 VATION OF THE BLOOD-VESSELS AND 
 VISCERA. 
 
CHAPTER I. 
 
 FORMATION AND RELATIONS OF THE SYMPATHETIC 
 SYSTEM. 
 
 The so-called sympathetic nervous system comprises the 
 outlying efferent neurons through which impulses from the 
 central nervous system finally reach the involuntary muscles 
 and glands. Though situated entirely in the periphery, 
 these neurons are connected with the anterior horns of a part 
 of the spinal cord, and with the oculo-motor, facial, glosso- 
 pharyngeal and pneumogastric nuclei. Their cell-bodies are 
 collected into ganglia, which are found in the region of the 
 head, along the vertebral column, in the prevertebral plexuses 
 and in the tissues of the viscera. There is also a large 
 number of small nerve-cells in the walls of the alimentary 
 tract, forming what are known as the plexuses of Meissner and 
 Auerbach, which may, or may not, be associated with the 
 sympathetic system, their function not being satisfactorily 
 determined. 
 
 Every efferent nerve path to the cell of an involuntary mus- 
 cle or gland consists of two distinct but connected neurons. 
 The fiber of the first neuron, arising in the brain or spinal 
 cord, passes out in a cranial or a spinal nerve and ends about 
 the dendrites of the second neuron, in one of the sympathetic 
 ganglia. The fiber of the second neuron completes the path. 
 The first fiber is generally medullated or white and termed 
 preganglionic; the second fiber is generally non-medullated 
 or gray and termed postganglionic, these terms signifying the 
 position of the fibers in relation to the ganglia. 
 
 (117) 
 
118 TBE SYMPATHETIC SYSTEM. 
 
 THE VERTEBRAL GANGLIA. 
 
 The vertebral ganglia lie in two chains along the front 
 of the vertebral column, from the second cervical vertebra to 
 the coccyx. The ganglia of each side are connected with one 
 another by a cord of nerve-fibers, the cords and the ganglia 
 forming the sympathetic trunks. Each trunk generally contains 
 from 20 to 23 ganglia, consisting of three cervical, eleven 
 or twelve thoracic, four lumbar, four sacral and one coccy- 
 geal, the last being common to both trunks and known as the 
 ganglion impar. 
 
 The preganglionic fibers that connect the vertebral ganglia 
 with the cord leave the cord in the thoracic and the first 
 two lumbar nerves — occasionally, also, in the next two 
 nerves below. As each of these nerves reaches the outside 
 of the vertebral column, its preganglionic fibers, branching 
 off in a white ramus communicans, pass to the nearest verte- 
 bral ganglion. Some of the fibers end in the first ganglion 
 that they enter; others, passing tbrough the first ganglion, 
 ascend or descend in the sympathetic trunk and end in a 
 higher or a lower ganglion; and still others, after passing 
 through one or more vertebral ganglia, continue as pregan- 
 glionic fibers and end in some ganglion of a prevertebral 
 plexus. These last fibers are known as the rami efferentes of 
 the ganglia that they traverse, and they always run in vis- 
 ceral nerves. 
 
 The white rami communicantes, in addition to their efferent 
 fibers, also contain sensory fibers of the viscera. These 
 fibers arise in the ganglia of the posterior nerve-roots, pass 
 through the white rami and the vertebral ganglia, and then 
 run in the visceral nerves to their destination in the viscera. 
 
 The postganglionic fibers of the vertebral ganglia form gray 
 rami communicantes, and sometimes, also, rami efferentes. 
 The rami efferentes generally enter prevertebral plexuses 
 and are thence distributed directly to blood-vessels or vis- 
 cera. The gray rami communicantes are small bundles that 
 
THE SUPERIOR CERVICAL GANGLION. 119 
 
 pass from each ganglion to the skeletal parts of one or 
 more of the neighboring spinal nerves. The majority of the 
 fibers in each gray ramus accompany the peripheral branches 
 of the nerve, particularly the cutaneous branches, being 
 finally distributed to the blood-vessels of the muscles and 
 skin, the erector muscles of the hair and the sweat glands. 
 Some of the fibers, however, instead of running peripherally, 
 pass back along the posterior nerve-root and re-enter the ver- 
 tebral canal, to suppy the blood-vessels of the spinal cord 
 and its membranes. The remaining fibers leave the gray 
 ramus before its junction with the nerve, some to accompany 
 the recurrent branch of the nerve to the vertebral canal, and 
 the others to follow and innervate the intercostal and lumbar 
 arteries. The gray rami, as a whole, contain vaso-constrictor, 
 vaso-dilator, pilo-motor and secretory fibers. 
 
 The Superior Cervical Ganglion. 
 
 The superior cervical ganglion, varying from an inch to an 
 inch and a half in length, lies on the front of the transverse 
 processes of the second and third cervical vertebrae, with the 
 internal carotid artery in front and the pneumogastric nerve 
 behind. The preganglionic fibers that connect it with the 
 spinal cord, leave the cord in the first five or six thoracic 
 nerves, pass through the white rami to the sympathetic 
 trunk, and thence upward in the trunk, to end about the 
 cells of the ganglion. Its postganglionic fibers form a gray 
 ramus for each of the first four cervical nerves. It dis- 
 tributes rami efferentes, as follows : 
 
 (1) Three branches, joining respectively the glosso-pharyn- 
 geal, pneumogastric and hypoglossal nerves, accompany 
 these nerves to parts in which they are distributed. 
 
 (2) Two or three pharyngeal branches, descending to the back 
 of the pharynx, join the pharyngeal plexus. 
 
 (3) The internal carotid branc ascending along the inner 
 side of the internal carotid artery to the carotid canal, there 
 
120 THE SYMPATHETIC SYSTEM. 
 
 divides into an inner and an outer division. The inner divi- 
 sion, continuing along the inner side of the artery to the 
 cavernous sinus, there breaks up and forms the cavernous 
 •plexus, the fibers from which are distributed to the third and 
 fourth cranial nerves, the ciliary ganglion and the pituitary 
 body. The outer division, while still in the carotid canal, 
 forms the carotid plexus about the artery. From this spring 
 the great deep petrosal nerve, which passes through the Vidian 
 canal to the spheno-palatine ganglion, and the small deep 
 petrosal nerve, which runs with the tympanic nerve to the 
 tympanic plexus in the petrous bone. It also gives off 
 branches that join the abducent and trifacial nerves, the 
 latter at the Gasserian ganglion. 
 
 (4) The external carotid branch, running with the external 
 carotid artery, forms on the facial artery a plexus from which 
 fibers pass to the sublingual and submaxillary ganglia, and 
 on the middle meningeal artery another plexus from which 
 fibers pass to the otic ganglion. 
 
 (5) Two or three superior cardiac branches, descending be- 
 hind the carotid sheath, enter the thorax and join the car- 
 diac plexus. 
 
 The Middle Cervical Ganglion. 
 
 The middle cervical ganglion lies on the front of the sixth 
 or seventh cervical vertebra. The fibers that connect it with 
 the cord, leave the cord in the upper five or six thoracic 
 nerves and reach the ganglion by way of the white rami 
 communicantes and the sympathetic trunk. Its postgang- 
 lionic fibers form a gray ramus for each of the fifth and sixth 
 cervical nerves and a ramus efferens that terminates in the 
 thyroid gland. A middle cardiac branch joins the cardiac 
 plexus. 
 
 The Inferior Cervical Ganglion. 
 
 The inferior cervical ganglion lies above the neck of the 
 
Plate 16. 
 
 The right sympathetic trunk : 1, middle cervical ganglion ; a, inferior cervical 
 ganglion ; 3, first thoracic ganglion ; 4, second thoracic ganglion ; 5, intercostal 
 nerve ; 6, rami oommunicantes ; 7, greater splanchnic nerve ; 9, the diaphragm.— 
 (Modified from Spalteholz,) 
 
THE THORACIC GANGLIA. 121 
 
 iSrst rib, covered by the vertebral artery. The preganglionic 
 fibers connecting it with the spinal cojrd leave the cord in the 
 upper six or seven thoracic nerves and reach the ganglion by 
 way of the white rami and the sympathetic trunk. Its post- 
 ganglionic fibers form a gray ramus for each of the seventh 
 and eighth cervical nerves, and rami eflerentes, as follows : 
 (a) branches distributed to neighboring blood-vessels; (b) 
 the inferior cardiac branch, which forms one of the accelerator 
 nerves of the heart and ends in the cardiac plexus, and (c) 
 branches that unite in a plexiform manner with branches of 
 the first thoracic ganglion and accompany the vertebral 
 artery into the cranium. 
 
 The Thoracic Ganglia. 
 
 The first thoracic ganglion lies under the head of the first 
 rib; the twelfth, on the side of the twelfth thoracic vertebra; 
 and the intervening ganglia, on the heads of the ribs. Each 
 of these ganglia is connected with the spinal cord bj' a white 
 ramus communicans, and each distributes a gray ramus to 
 one of the thoracic nerves. The first ganglion gives off to 
 the cardiac plexus a ramus efferens that forms an accelerator 
 nerve of the heart. The second, third and fourth ganglia 
 distribute rami efferentes to the pulmonary plexus, and the 
 upper five ganglia distribute other rami efferentes to the 
 plexus about the aorta. The lower six or seven ganglia 
 give off rami efferentes that form the great splanchnic, small 
 splanchnic and least splanchnic nerves. 
 
 The great splanchnic nerve is formed on the side of the 
 vertebral column by the union of rami efferentes of the 
 ganglia from the fifth or sixth to the ninth or tenth. The 
 small splanchnic nerve is formed by the union of rami effer- 
 entes from the ninth and tenth ganglia, and sometimes, also, 
 from the eleventh. The least splanchnic nerve is a ramus 
 efferens of the twelfth ganglion. All these nerves pass 
 through the diaphragm into the abdomen and join preverte- 
 
122 THE SYMPATHETIC SYSTEM. 
 
 bral plexuses. Their efferent fibers end about sympathetic 
 cells. 
 
 The Lumbar Ganglia. 
 
 The lumbar ganglia lie on the front of the bodies of the 
 lumbar vertebrae. The first and second ganglia are each 
 connected with the spinal cord by the white ramus com- 
 municans of the corresponding lumbar nerve. But the third 
 and fourth ganglia are connected by fibers that arise at 
 higher levels and pass to the ganglia by way of the sympa- 
 thetic trunk, there being, as a rule, no white rami below the 
 second lumbar nerve. The postganglionic fibers of the lum- 
 bar ganglia form a gray ramus communicans for each of the 
 lumbar nerves. Their rami efferentes, containing pregang- 
 lionic fibers, join the neighboring prevertebral plexuses. 
 
 The Sacral Ganglia. 
 
 The sacral ganglia are situated on the front of the sacrum 
 along the inner side of the anterior sacral foramina. They 
 distribute a gray ramus to each of the sacral nerves and rami 
 efferentes to the neighboring plexuses. But white rami in 
 this region are wanting, the preganglionic connection of the 
 ganglia being derived through nerves at a higher level, by 
 way of the sympathetic trunk. The second, third and fourth 
 sacral nerves, however, contain preganglionic fibers, and 
 these unite to form the nervus erigens. This enters the pelvic 
 plexus and ends bj' arborization in pelvic ganglia, without 
 making any connection with the sympathetic trunk. It 
 contains viscero-motor, viscero-inhibitory and vaso-dilator 
 fibers. 
 
 Below the sacrum the two sympathetic trunks unite in 
 the ganglion impar, which is also connected with the coccy- 
 geal nerves. 
 
THE GANGLIA OF THE READ REGION. 123 
 
 THE GANGLIA OF THE HEAD REGION. 
 
 The sympathetic system, continuing upward into the 
 head, is here represented by the ciliary, spheno-palatine, 
 otic, sublingual and submaxillary ganglia. These ganglia 
 are each traversed by fibers of the trifacial nerve, as shown 
 in previous chapters, and by the sympathetic fibers that 
 reach them through the carotid branches of the superior cer- 
 vical ganglion, both sets of fibers, after passing through the 
 ganglia, being distributed from their peripheral side. 
 
 The Ophthalmic, Ciliary or Lenticular Ganglion is a 
 small quadrangular body, about one-twelfth of an inch in its 
 long diameter, lying in the back of the orbital fossa, between 
 the optic nerve and the external rectus muscle. The pre- 
 ganglionic fibers that connect it with the central nervous 
 system arise in the oculo-motor nucleus, pass through the 
 oculo-motor nerve and its branch to the inferior oblique 
 muscle of the eyeball, and then branch off as a short bundle 
 and pass to the ganglion. Its postganglionic fibers run in 
 the short ciliary nerves and supply the ciliary muscle and the 
 sphincter muscle of the iris. 
 
 The Spheno-palatine or Meckel's Ganglion is a small 
 triangular bodj', about one-fifth of an inch long, lying under 
 the superior maxillary nerve in the fat of the spheno-maxil- 
 lary fossa. Its central connections are with the facial nucleus. 
 The preganglionic fibers run in the facial nerve as far as the 
 geniculate ganglion, and then branch ofE in the great super- 
 ficial petrosal nerve, in which they complete their course. This 
 nerve, leaving the petrous bone through a foramen on its 
 anterior surface, runs thence through the foramen lacerum 
 •medium to the under surface of the cranium, where it turns 
 forward and passes to the ganglion by way of the Vidian 
 canal. The fibers arising in the ganglion accompany 
 branches of the superior maxillary nerve and are distributed 
 to blood-vessels. 
 
 The Otic Ganglion is a small oval body, about one- 
 
124 THE SYMPATHETIC SYSTEM. 
 
 sixth of an inch in its long diameter, lying under the base of 
 the cranium near the foramen ovale, with the Eustachian 
 tube on its inner side. Its central connections are with the 
 glosso-pharyngeal nucleus. The preganglionic fibers pass 
 with the tympanic nerve into the petrous bone and there 
 divide into two divisions, one of which joins the great super- 
 ficial petrosal nerve, and the other, uniting with the small 
 superficial petrosal nerve, runs with this to the otic ganglion. 
 The course of the small superficial petrosal nerve is from the 
 geniculate ganglion through a foramen on the anterior surface 
 of the petrous bone, and thence out of the cranium between 
 the petrous bone and the great wing of the sphenoid. Be- 
 neath the cranium it passes to the otic ganglion, where the 
 glossopharyngeal fibers end. The fibers from the ganglion 
 are distributed mainly with the mandibular division of the 
 trifacial nerve, their destination being the blood-vessels of 
 the parts which this division supplies, and the parotid and 
 orbital glands. They are both vaso-dilator and secretory in 
 function. 
 
 The Sublingual Ganglion is a small body about the size 
 of a pin-head, situated in the floor of the mouth, with the 
 lingual nerve above and Wharton's duct belovf. The Sub- 
 maxillary Ganglion is a still more minute body, lying in 
 the hilum of the submaxillary gland. The fibers that con- 
 nect these ganglia with the central nervous system, arise in 
 the nucleus of the facial nerve and reach the ganglia by way 
 of the facial and chorda tympani nerves. The fibers from 
 the submaxillary ganglion are distributed to the submaxil- 
 lary gland and its blood-vessels. The fibers from the sub- 
 lingual ganglion join the lingual nerve and with this are dis- 
 tributed to the sublingual gland and its blood-vessels and to 
 the anterior two-thirds of the tongue. The fibers from both 
 ganglia are in part vaso-dilator and in part secretory. 
 
TSE PBEVEttTEBitAL PLEXXJSES. 125 
 
 THE PREVERTEBRAL PLEXUSES. 
 
 These are the plexuses through which the cerebro-spihal 
 nerves are distributed to the visceral organs and their blood- 
 vessels. The main prevertebral plexuses are the cardiac, 
 pulmonary, solar, hypogastric and pelvic. 
 
 The Cardiac Plexus, lying in the concavity of the aortic 
 arch and in the bifurcation of the trachea, is formed by 
 branches of the pneumogastric nerves and rami efferentes of the 
 cervical and first thoracic ganglia. It contains the ganglion 
 of Wrisberg and other small ganglia and gives rise to the right 
 and left coronary plexuses, which accompany the corresponding 
 arteries of the heart. The efferent fibers that enter it are 
 derived from the pneumogastric nerves and the inferior 
 cervical and stellate ganglia. 
 
 The Pulmonary Plexuses are two in number for each 
 lung — the anterior, lying in front of the bronchus, and the 
 posterior, lying behind the root of the lung. They are 
 formed by pneumogastric fibers and by rami efferentes of the 
 second, third and fourth thoracic ganglia. Their branches 
 are distributed to the bronchi and the pulmonary blood- 
 vessels. 
 
 The Solar or Epigastric Plexus, lying in front of the ' 
 upper two lumbar vertebrae, behind the stomach and be- 
 tween the upper ends of the kidneys, consists of two lateral 
 parts connected by fibers extending across the aorta and sur- 
 rounding the origin of the coeliac axis. It is formed by 
 pneumogastric fibers and the great splanchnic and small 
 splanchnic nerves. Its principal ganglia are the semi-lunar 
 and the aortico-renal, in each half of the plexus, and the supe- 
 rior mesenteric, in the right half- only. Arising from it are the 
 phrenic, hepatic, coronary, superior mesenteric, splenic and 
 aortic plexuses, which accompany the blood-vessels of the 
 corresponding names. 
 
 The aortic plexus, beginning with fibers from the lower end 
 of the solar plexus, is re-enforced by rami efferentes from 
 
126 THE SYMPATSETlC SYSTEM. 
 
 the upper lumbar ganglia. As two lateral cords connected 
 by intervening fibers, it descends on the aorta as far as 
 the front of the fifth lumbar vertebra and there ends in the 
 hypogastric plexus. Its main branch forms the inferior mes- 
 enteric plexus, which follows the course of the inferior mesen- 
 teric artery and holds in its meshes the inferior mesenteric 
 ganglion. Its other branches unite with branches of the 
 solar plexus and with the least splanchnic nerve, the union 
 forming the renal and supra-renal plexuses. These follow the 
 course of the renal and supra-renal arteries and distribute 
 fibers to the kidney and supra-renal body and the ureter and 
 spermatic cord. 
 
 The Hypogastric Plexus is a strong meshwork of fibers 
 derived from the aortic plexus and the lower lumbar ganglia. 
 It serves principally as a connecting link between the plex- 
 uses of the abdomen and the pelvis. 
 
 The Pelvic Plexus begins with two lateral groups of 
 fibers derived from the lower end of the hypogastric plexus. 
 These descend on each side of the rectum and bladder in the 
 male, and of the rectum, bladder and vagina in the female. 
 On reaching the pelvis they are augmented by the nervus eri- 
 gens and by rami efferentes from the sacral ganglia. This 
 plexus contains many small collections of sympathetic nerve- 
 cells, the preganglionic connections of which are with the 
 lumbar and sacral segments of the spinal cord. Its secondary 
 plexuses are the hemorrhoidal and vesical (in both sexes), 
 the prostatic (in the male), and the uterine and vaginal (in 
 the female). 
 
 The hemorrhoidal plexus descends on the middle hemor- 
 rhoidal artery, where fibers • descending from the inferior 
 mesenteric plexus join it. It supplies the walls and blood- 
 vessels of the rectum and the internal sphincter of the anus. 
 
 The vesical plexus extends over the base and sides of the 
 bladder. Its branches are distributed to the bladder walls 
 and blood-vessels, and, in the male, to the vasa deferentia 
 and the seminal vesicles. 
 
TBE PREVERTESttAL PLEXUSES. 127 
 
 The prostatic plexus lies between the prostate gland and the 
 levator ani muscle. It supplies the gland and contributes 
 somewhat to the innervation of the seminal vesicles and the 
 corpus oavernosum. 
 
 The uterine plexus accompanies the broad ligament, being 
 distributed to the uterus, ovaries and Fallopian tubes. 
 
 The vaginal 'plexus lies in the walls of the vagina. It sup- 
 plies the blood-vessels, mucous membrane and muscles of 
 the vagina and distributes some fibers to the clitoris. Among 
 its efferent fibers are some that are under voluntary control. 
 
CHAPTER II. 
 
 INNERVATION OF THE BLOOD-VESSELS. 
 
 The vaso-constrictor nerves (preganglonic fibers) for the 
 whole body have their cells of origin in the spinal cord and 
 leave the cord in the thoracic and first two lumbar nerves. 
 The vaso-dilator nerves (preganglionic fibers) are of both 
 spinal and cranial origin. The spinal dilator fibers leave 
 the cord in the thoracic and first two lumbar nerves and in 
 the second, third and fourth .sacral nerves. The cranial 
 dilator fibers arise in the facial, glossopharyngeal and pneu- 
 mogastric nuclei and leave the brain in the facial, glosso- 
 pharyngeal and pneumogastric nerves. The vaso-motor 
 nerves, both constrictor and dilator, of thoracic and lumbar 
 origin, pass through the white rami communicantes to the sym- 
 pathetic trunks. Those destined for skeletal parts of the body 
 and for all structures in the head, end by arborization in ver- 
 tebral ganglia. Those destined for visceral organs — with two 
 exceptions — pass through the vertebral ganglia and end by 
 arborization in prevertebral ganglia. The sacral dilator nerves 
 make no connection with the. sympathetic trunks but pass 
 directly to prevertebral ganglia in the pelvis. 
 
 VASO-MOTOR NERVES OF THE HEAD REGION. 
 
 The vaso-constrictor nerves of the head region leave the 
 cord in the upper five or six thoracic nerves and reach their 
 destination as postganglionic fibers from the superior cervical 
 ganglion, being distributed with both cranial and cervical 
 nerves. 
 
 The vaso-dilator nerves arise in the upper five or six tho- 
 (128) 
 
THE NECK, TB.VNK AND LIMBS. 129 
 
 racic nerves and in the facial and glossopharyngeal nerves. 
 The dilator fibers of spinal origin pass to the superior cer- 
 vical ganglion, and from this, as postganglionic fibers, their 
 course is continued to the cheeks, lips, gums, palate and 
 nasal fossse and to the scalp and external ear. Of the facial 
 fibers a part pass to the spheno-palatine ganglion. From 
 this the postganglionic fibers are distributed with the tri- 
 facial fibers by which the ganglion is traversed, i. e., in 
 the mucous membrane of the upper lip, the upper part of the 
 mouth, the soft palate, the tonsils, the nasal fossse and the 
 upper part of the pharynx. Other facial fibers pass to the 
 sublingual ganglion, from which the postganglionic fibers are 
 distributed in the sublingual gland and in the mucous mem- 
 brane of the anterior two-thirds of the tongue. The remaining 
 facial fibers pass to the submaxillary ganglion, and from this 
 the postganglionic fibers are distributed in the gland of tlie 
 same name. The glossopharyngeal fibers pass to the otic gan- 
 glion, from which the postganglionic fibers are distributed 
 with the mandibular division of the trifacial nerve, their 
 destination being the skin of the temples, the skin and mu- 
 cous membrane of the cheeks, the lower lip and lower gums, 
 the posterior third of the tongue and the parotid and orbital 
 glands. 
 
 VASO-MOTOR NERVES OF THE NECK, TRUNK AND LIMBS. 
 
 The vaso-motor nerves, both constrictor and dilator, for 
 the cervical region leave the cord in the upper five or six 
 thoracic nerves and pass mainly to the superior cervical 
 ganglion, though some end in the two ganglia below. From 
 these ganglia postganglionic fibers accompany the cervical 
 nerves to the muscles and skin of the neck. 
 
 The vaso-motor nerves, both constrictor and dilator, for 
 the upper limb leave the cord in the upper five or six thoracic 
 nerves and pass to the first thoracic ganglion, from which, as 
 10 
 
130 INNERVATION OF THE BLOOD-VESSELS. 
 
 postganglionic fibers, they are distributed with the terminal 
 branches of the brachial plexus. 
 
 The vaso-motor nerves, both constrictor and dilator, for 
 the lower limb leave the cord in the lower thoracic and the 
 first two lumbar nerves and pass to the lower lumbar and 
 the upper sacral ganglia, from which, as postganglionic 
 fibers, their course is continued in branches of the lumbar 
 and sacral plexuses. 
 
 The v£tso-motor nerves, both constrictor and dilator, for 
 the trunk arise throughout the entire vaso-motor area of the 
 cord and ])ass to all the vertebral ganglia below the superior 
 cervical. Thence, as postganglionic fibers, they accompany 
 all the spinal nerves that are distributed in the trunk. 
 
 VASO-MOTOR NERVES OF THE TONSILS, PHARYNX 
 AND LARYNX. 
 
 The vaso-constrictor nerves for these parts leave the cord 
 in the ujjper five or six thoracic nerves and are distributed as 
 postganglionic fibers from the superior cervical ganglion. The 
 vaso-dilator nerves are derived to some extent from the facial 
 nerve, as previously stated. But their main source is the 
 nucleus ambiguus, from which they emerge in either the 
 glossopharyngeal or the pneumogastric nerve. Their cell 
 stations are in or near the parts to which as postganglionic 
 fibers they are eventually distributed. 
 
 VASOMOTOR NERVES OF THE SPINAL CORD. 
 
 The vaso-motor nerves, both constrictor and dilator, for 
 the spinal cord and its membranes leave the cord in the 
 thoracic and the first two lumbar nerves and pass to the 
 vertebral ganglia. Thence, as postganglionic fibers, they 
 enter the gray rami communicantes and pass to the vertebral 
 canal, some passing by way of the posterior roots of the 
 spinal nerves, and the remainder by way of their recurrent 
 branches. 
 
THE BRAIN, HEART AND LUNGS. 131 
 
 VASO-MOTOR NERVES OF THE BRAIN. 
 
 The blood-supply of the brain is regulated, to a consider- 
 able extent, by vaso-motor activity in other parts of the 
 body. Mental activity is accompanied by a vaso-constriction 
 in the skin and abdomen, the result of which is less blood in 
 these regions and more blood in the brain. A lessening or 
 cessation of mental activity is accompanied by a vascular re- 
 laxation in the skin and abdomen, and in this case the result 
 is more blood in these regions and less blood in the brain. 
 The anatomical relations by which this adjustment of the 
 cerebral circulation is effected are uncertain, though it is 
 probably brought about through fibers extending from the 
 cortex of the cerebrum to the vaso-constrictor center. 
 
 Besides this indirect or reflex control of the cerebral circu- 
 lation, there is evidence that the brain is also supplied with 
 both vaso-constrictor and vaso-dilator nerves which arise in 
 the second, third and fourth thoracic nerves and reach the 
 brain by way of the superior cervical gangUon and its internal 
 carotid branches. To what relative extent these nerves are 
 factors in regulating the brain circulation, has not been finally 
 determined. 
 
 VASOMOTOR NERVES OF THE HEART. 
 
 Vaso-motor nerves of the heart have not been conclusively 
 demonstrated, but such evidence as there is points to the 
 following: That constrictor nerves are received by way of the 
 upper two or three thoracic nerves and either the first tho- 
 racic or the inferior cervical ganglion, and that dilator nerves 
 are derived through the pneumogastric nerves and ganglia 
 located in the region of the heart. 
 
 VASOMOTOR NERVES OF THE LUNGS. 
 
 These nerves, too, are a matter of some uncertainty, but, 
 so far as they have been investigated, the evidence is that 
 both constrictor and dilator nerves leave the cord in the 
 
132 INNERVATION OF THE BLOOD-VESSELS. 
 
 thoracic nerves, from the third to the seventh, and pass to 
 the second, third and fourth thoracic ganglia, being thence 
 distributed, as postganglionic fibers, to the bronchial arte- 
 ries. The pulmonary arteries have no vaso-raotor nerves, so 
 far as known. 
 
 VASO-MOTOR NERVES OF THE ABDOMINAL ORGANS. 
 
 The vaso-constrictor nerves for the stomach, liver, spleen 
 and pancreas, and for the intestine down to the sigmoid 
 colon, arise in the spinal nerves, from the fourth or fifth tho- 
 racic to the second lumbar, and pass to the semi-lunar, 
 aortico-renal, superior mesenteric and inferior mesenteric 
 ganglia, from which, as postganglionic fibers, they are dis- 
 tributed by way of the solar plexus and its branches. The 
 vaso-dilator nerves for the descending colon and the left 
 half of the transverse colon arise in the spinal nerves, from 
 the sixth thoracic to the second lumbar, and reach their 
 destination by way of the inferior mesenteric ganglion and 
 the inferior mesenteric plexus. The vaso-dilator nerves for 
 the remaining organs here considered arise in the pneumo- 
 gastric nerves and pass to the various blood-vessels as post- 
 ganglionic fibers from ganglia of the solar plexus. 
 
 The kidneys and the supra-renal bodies receive both vaso- 
 constrictor and vaso-dilator nerves from the spinal cord. 
 They leave the cord, for the most part, in the eleventh and 
 twelfth thoracic and the first two lumbar nerves and end 
 mainly in the aortico-renal ganglion. Thence, as postgang- 
 lionic fibers, they follow the course of the renal and the 
 supra-renal blood-vessels. 
 
 VASO-MOTOR NERVES OF THE SIGMOID COLON AND 
 RECTUM. 
 
 The vaso-constrictor nerves for these parts of the intestine 
 leave the cord in the tenth, eleventh and twelfth thoracic and 
 the first two lumbar nerves and pass to tbe inferior mesen- 
 teric ganglion, from which postganglionic fibers, forming the 
 
THE GENITAL ORGANS AND BLADDER. 133 
 
 hypogastric nerve, continue the path. The vaso-dilator nerves 
 arise in the second, third and fourth sacral nerves and pass 
 to pelvic ganglia, from which, as postganglionic fibers, they 
 are distributed in branches of the pelvic plexus. 
 
 VASO-MOTOR NERVES OF THE EXTERNAL GENITAL 
 ORGANS. 
 
 The vaso-constrictor nerves for the external genital organs 
 leave the cord in the first two lumbar nerves and pass to 
 sacral ganglia, being thence distributed, as postganglionic 
 fibers, in branches of the pudic nerve. The vaso-dilator 
 nerves arise in the nervus erigens and pass to pelvic ganglia, 
 from which, as postganglionic fibers, they follow the course 
 of the blood-vessels. 
 
 VASO-MOTOR NERVES OF THE INTERNAL GENITAL 
 ORGANS AND THE BLADDER. 
 
 The vaso-constrictor nerves of the internal genital organs 
 leave the cord in the first two lumbar nerves and pass to the 
 inferior mesenteric ganglion, from which, as postganglionic 
 fibers, they are distributed in the hypogastric nerve. The 
 vaso-dilator nerves arise in the nervus erigens and are dis- 
 tributed as postganglionic fibers from pelvic ganglia. 
 
 The vaso-motor nerves of the bladder, both constrictor 
 and dilator, have practically the same origin and course as 
 the corresponding nerves of the internal genital organs, the 
 main difference being only in their destination. 
 
CHAPTER III. 
 
 FUNCTIONS AND PROPERTIES OF THE VASO-MOTOR 
 NERVES. 
 
 The Vaso-constrictor Nerves. 
 
 The effect of vaso-constrictor activity is to maintain the 
 muscular tone and the normal caliber of the blood-vessels, 
 thus regulating, to a large extent, the arterial pressure and 
 the flow of the blood. 
 
 The controlling factor in vaso-constriction is the vaso- 
 constrictor center in the medulla, from which the fibers 
 pass down the lateral columns of the cord and end about the 
 vaso-constrictor neurons in the anterior horns of the spinal 
 gray matter. The center is motor in function and -is con- 
 stantly active, its activity being maintained, and, for the 
 most part, regulated, reflexly — that is, by impulses received 
 through afferent nerves. The nerves which convey the regu- 
 lating impulses are of two classes, pressor nerves and depressor 
 nerves. Pressor nerves are those whose impulses increase the 
 activity of the center and thereby cause an increased con- 
 striction of the arterioles and a rise of arterial pressure. De- 
 pressor nerves are those whose impulses inhibit the activity 
 of the center and thereby .cause a relaxation of the arterioles 
 and a fall of arterial pressure. Most of the larger nerve- 
 trunks contain both pressor and depressor fibers, though the 
 pressor fibers predominate, and whether the stimulation of a 
 nerve-trunk gives a pressor or a depressor effect, depends 
 upon which set of fibers respond to the stimulus. 
 
 Common and well-known effects of both pressor and de- 
 pressor activity are those produced by the influences of 
 
 (134) 
 
THE VASO-CONSTRIOTOB NERVES. 135 
 
 thermal stimuli. A brief application of cold to the skin, for 
 example, whether by exposure or otherwise, results in 
 blanching, due to the fact that the nerves which first respond 
 to the cold stimulus have a pressor effect on the vaso-con- 
 strictor center, or some part of it, and reflexly increase the 
 constriction of the cutaneous vessels, thereby diminishing 
 the flow of blood in the skin. The subsequent reddeping of 
 the skin from the flushing of the cutaneous vessels, when the 
 cold stimulus is applied for a considerable time, may be 
 either the reflex effect of a secondary stimulation of the de- 
 pressor fibers, or, what is more probable, the result of a reflex 
 vaso-dilation. Heat, though at first reflexly stimulating the 
 vaso-dilator nerves, if applied for a sufficient period of time 
 and over a sufficient area of the body, eventually has a de- 
 pressor effect on the vaso-constrictor center, the result of 
 which is a vascular relaxation with a lowering of arterial tone 
 and arterial pressure. Atmospheric temperature, acting as it 
 does on the whole surface of the body, has most important 
 effects, both pressor and depressor in character, on the vaso- 
 constrictor center and corresponding influences on the circu- 
 lation. 
 
 A marked example of depressor activity is that manifested 
 by the depressor nerve of the heart, formed by afferent fibers of 
 the pneumogastric nerve. If the arterioles become con- 
 stricted to the extent of creating a peripheral resistance that 
 the heart is unable to overcome, the depressor nerve is 
 mechanically stimulated, the effect of the stimulation is 
 transmitted to the vaso-constrictor center, the activity of the 
 center is diminished and the constriction of the arterioles re- 
 duced, enabling the heart to resume its normal contractions, 
 
 Though the action of the vaso-constrictor center is regu- 
 larly maintained by the stimulus of afferent impulses, it is 
 modified, to a considerable extent, by conditions in the cere- 
 bral cortex. Mental work, as previously explained, has a 
 stimulating effect on certain parts of the center, with the 
 
136 THE VASO-MOTOS NERVES. 
 
 final and important result that the blood is increased in the 
 brain. Emotional conditions have various effects. Sudden 
 fear, for example, accelerates the center and increases vascu- 
 lar constriction, which, in case of the cutaneous vessels, is 
 manifested by pallor of the skin. Some other emotions — 
 embarrassment, for instance — inhibit the center. Causing 
 vascular relaxation and the increased blood-flow that is seen 
 in the face as a blush. Mental depression tends to render 
 the center increasingly susceptible to all the influences that 
 play upon it, and if such conditions are long continued, the 
 center finally becomes fatigued, control of the circulation is 
 diminished, blood-pressure is abnormally reduced and patho- 
 logical consequences ultimately ensue. On the other hand, 
 normal mental states are potent factors in preserving the 
 tonic activity of the center and, consequently, in maintain- 
 ing the normal flow of the blood. 
 
 As is now evident, the action of the yaso-constrictor 
 nerves, under normal conditions, is determined by the im- 
 pulses discharged by the vaso-constrictor center, but there is 
 evidence that they are also capable of independent action, 
 under the stimulus of afferent impulses transmitted directly 
 to the nerves themselves. In spinal traumata, in which the 
 connection is broken between any of the peripheral nerves and 
 the controlling vaso-constrictor center, the blood-vessels that 
 receive their innervation from the part of the cord below the 
 injury immediately lose their tone. But after a time, even 
 with a continuance of the lesion, the lost tone is more or less 
 restored, and the restoration must be attributed, for the most 
 part, to the property of independent action inherent either in 
 the spinal or the sympathetic neurons whose fibers form the 
 vaso-constrictor nerves. There is some evidence that both 
 sets of neurons possess this property in some degree. Its 
 importance in certain pathological conditions of the spinal 
 cord, especially in a limited lateral sclerosis, cannot be over- 
 estimated, 
 
THE VASO-DILATOR NERVES. 137 
 
 The Vaso-dilator Nerves. 
 
 Vaso-di]ator activity lessens the contraction of the circular 
 muscles of the arterioles, as a result of which the vessels are 
 expanded and the quantity of blood which they contain is 
 increased. The vaso-dilator nerves, unlike the vaso-con- 
 strictor nerves, are not constantly active, nor, so far as* 
 known, are they controlled from a general center. Under 
 normal conditiors, their activity is displayed only at the 
 same time and in the same degree as that of their respective 
 organs, the effect of which, under such conditions, is an in- 
 crease in the blood-supply of the organs, in proportion to 
 their functional needs. Their activity is modified in some 
 instances by mental states and mental processes, the chorda 
 tympani nerve and the nervus erigens, for example, being 
 especially sensitive to cerebral influences. It is also possi- 
 ble that blushing, under the influence of embarrassing emo- 
 tions, is another event assignable to the same cause, though, 
 in this case, since the vaso-dilation extends to other parts 
 than the face, it seems more probable, as previously observed, 
 that the effect is produced by inhibition of the vaso-con- 
 strictor center. An important property of these nerves is a 
 high degree of irritability with a corresponding responsive- 
 ness to abnormal stimuli, and in acute disorders, particularly 
 when of an irritative character, vaso-dilation is one of the 
 earliest and most constant manifestions. 
 
 All vaso-dilation assumes a previous vaso-constriction to a 
 greater or less extent. Consequently the effects of vaso- 
 dilator activity will depend not only upon the strength of the 
 reflex stimulus but also upon the muscular tone of the ves- 
 sels, the greatest effects, under a given stimulus and on a 
 given set of vessels, being produced when the vessels are in 
 the highest state of tone. Vaso-dilation in one part is nor- 
 mally accompanied by a compensatory vaso-constriction in 
 other parts. Otherwise, the vaso-dilation would be ineffec- 
 tive in the way of increasing the blood-supply, and the gen- 
 Pfal arterial pressure would be abnormallpr reducecj, 
 
CHAPTER IV. 
 
 INNERVATION OF THE VISCERAL ORGANS AND THE 
 PHYSIOLOGICAL ACTION OF THE VISCERAL NERVES. 
 
 The Iris and the Ciliary Muscle. 
 
 The efferent (pupillo-dilator) fibers, which supply the 
 dilator pupillae muscle of the iris, arise from a group 
 of cells situated in the lower cervical region of the cord and 
 known as the cilio-spinal center. The fibers leave the cord in 
 the first and second thoracic nerves and ascend in the sym- 
 pathetic trunk to the superior cervical ganglion, from which 
 postganglionic fibers, passing first with the ophthalmic divi- 
 sion of the fifth nerve and then with the nasal nerve and the 
 long ciliary nerves, continue the path to the muscle. The 
 afferent path from the eye to the cilio-spinal center is along 
 the optic nerve to the midbrain, and thence by new fibers 
 which arise in the midbrain and descend to the center in the 
 cord. 
 
 The efferent (pupillo-constrictor) fibers, which supply the 
 ciliary muscle and the sphincter muscle of the iris, arise in 
 the nucleus of the third cranial nerve and pass to the ciliary 
 ganglion, from which their course to the muscles is continued 
 by postganglionic fibers running in the short ciliary nerves. 
 The afferent path from the eye to the motor center is along 
 the optic nerve to the anterior quadrigemina, and thence by 
 other fibers which pass to the anterior part of the oculo- 
 motor nucleus, where the motor cells lie. 
 
 When the dilator fibers are stimulated, the radiating fibers 
 of the dilator-pupillse muscle are contracted, the iris is drawn, 
 back and the pupil is enlarged. 
 
 (138) 
 
THE HEART. 139 
 
 When the fibers to the sphincter of the iris are stimulated, 
 the sphincter is contracted, the iris is drawn forward and the 
 size of the pupil is diminished. 
 
 When the fibers to the cihary muscle are stimulated, 
 the muscle is contracted and the shortening of the muscle 
 pulls forward the choroid coat of the eyeball, thereby lessen- 
 ing the tension of the suspensory ligament of the lens and 
 enabling the lens to increase its convexity. This is "a reflex 
 act and is known as the accommodation reflex, but it occurs 
 only in connection with the voluntary act of adjusting the 
 eyes to near objects — an act which, in addition to the con- 
 traction of the ciliary muscle, involves also contraction of 
 the internal recti muscles, causing the eyes to converge, 
 and contraction of the sphincter of the iris, by which, in 
 consequence of the diminution in the size of the pupil, the 
 light rays are better focused on the retina. 
 
 The activity of the motor cells whose fibers supply the 
 constrictor and dilator muscles of the iris is normally deter- 
 mined in the act of accommodation and by the reflex stimu- 
 lation of light acting on the retina. Modifications of their 
 normal activity occur under the influences of impulses from 
 the cerebral cortex and of sensory impulses from peripheral 
 parts of the body. The emotional state of fear or the sen- 
 sation of pain, for instance, will have an inhibitory effect 
 on the cells of the constrictor fibers and cause dilation of 
 the pupils, while other emotional states and other kinds of 
 sensations may cause constriction. There are also drugs by 
 the action of which the size of the pupil may be modified, 
 those that cause constriction being known as miotics, and 
 those that cause dilation, as mydriatics. But in these cases 
 the action of the drug is sometimes exerted on the nerves 
 and sometimes directly on the muscles. 
 
 The Heart. 
 
 The heart receives inhibitory fibers through the pneumg- 
 
140 INNERVATION OF THE VISOEBAL ORGANS. 
 
 gastric nerves and cardiac ganglia, and motor (accelerator) 
 fibers through the second, third and fourth thoracic nerves 
 and the front thoracic and inferior cervical ganglia. 
 
 The inhibitory fibers, under moderate stimulation, slow 
 the action of the heart, and, under stronger stimulation, also 
 diminish the force of the beat. It is not believed, however, 
 that the different effects are produced by different fibers. 
 
 When the accelerator fibers are stimulated, the action of 
 the heart is quickened, and, in some cases, the strength of 
 the beat is increased. In this case it is probable that the 
 different effects are produced by the action of different fibers, 
 those that increase the force of the beat being known as 
 augmentor fibers. Some of the fibers which pass by way 
 of the stellate ganglion are believed to have an augmenting 
 function. 
 
 The cardio-inhibitory center — the group of cells that give 
 rise to the inhibitory fibers in the medulla — is kept in more 
 or less constant or tonic activity by the influences of im- 
 pulses constantly received through afferent nerves. By the 
 same influences its activity may also be modified. The 
 afferent fibers, the stimulation of which is most effective in 
 this respect are those distributed in the respiratory tract and 
 the abdominal viscera. A blow on the abdomen (the so- 
 called solar plexus blow) will so inhibit the action of the 
 heart as to cause fainting, and a blow of sufficient force on 
 the larynx will cause death. These effects are produced re- 
 flexly through afferent fibers of the pneumogastric nerves. 
 Less effects, both accelerating and inhibitory in their nature, 
 may be produced by stimulation of afferent nerves in other 
 parts of the body. The activity of the center is also affected 
 by emotional states, through the intercentral fibers connect- 
 ing the cortex and medulla. 
 
 The cells that form the accelerator center are in the cervi- 
 cal part of the cord, but their exact location has not been 
 determined, The fact that the accelerator fibej^ may bg 
 
THE OESOFBAGVS AlfD BRONCBt. 141 
 
 influenced to a considerable extent by stimulation of the 
 lower cervical nerves, would seem to indicate that, at least, a 
 part of the center is in the lower cervical region. And it is 
 not improbable that it extends upward as high as the 
 medulla. This center, like the inhibitory center, is nor- 
 mally in tonic activity and is subject in the same way to 
 stimulation and inhibition by cerebral and sensory impulses. 
 Besides its efferent fibers, the heart is also supplied with 
 the depressor nerve, consisting of afferent fibers, the stimula- 
 tion of which has an inhibitory effect on the vaso-constrictor 
 center and thereby removes any excess of peripheral resist- 
 ance that the heart may at any time be laboring to overcome. 
 This mechanism, by diminishing the force of the heart beat, 
 conserves the energy of the heart. 
 
 The Oesophagus. 
 
 The oesophagus receives motor fibers, and its cardiac 
 sphincter receives inhibitory fibers, through the pneumo- 
 gastric nerves and ganglia in the oesophageal walls. These 
 fibers are reflexly stimulated when food enters the oeso- 
 phagus, and their activity causes peristalsis of the oesopha- 
 gus and relaxation of the sphincter, the effect of which is the 
 passage of food into the stomach. The afferent fibers, the 
 stimulation of which incites the reflex, are of pneumogastric 
 origin. 
 
 The Bronchi. 
 
 Physiological investigations have demonstrated that the 
 bronchi are supplied with motor (broncho-constrictor) and 
 with inhibitory (broncho-dilator) fibers through the pneumo- 
 gastric nerves and ganglia of the pulmonary plexuses and 
 bronchial walls. There is clinical evidence that constrictor 
 fibers are also received from the thoracic part of the spinal 
 cord their origin being within the area extending approxi- 
 mately from the third to the seventh segment. Stimulation 
 
142 INNERVATION OF THE VISCERAL ORGANS. 
 
 of the constrictor fibers narrows the bronchi, and stimulation 
 of the dilator fibers widens them, the resistance to the in- 
 going and outgoing currents of air being increased in the one 
 case and diminished in the other. The conditions under 
 which the two sets of fibers are normally stimulated have 
 not been determined, nor has it been shown that the con- 
 strictor fibers, like motor fibers in general, are in tonic 
 activity. They are excessively active, however, in asthma, 
 and are reflexly stimulated when injurious gases come in 
 contact with the nasal mucous membrane, their action in the 
 latter case being protective. 
 
 The Stomach, Small Intestine, Ascending and 
 Transverse Colon. 
 
 The motor fibers of these parts are derived through the 
 pneumogastric nerves and ganglia of the solar plexus and 
 its derivatives. The inhibitory fibers are derived through 
 the splanchnic nerves, those for the stomach leaving the cord 
 in the thoracic nerves from the fifth to the eighth or ninth, 
 and those for the intestines in the nerves from the sixth tho- 
 racic to the first or second lumbar. Both sets of fibers are 
 ■normally stimulated reflexly, and their activity regulates the 
 gastric and intestinal movements. Their action, however, 
 may be affected by psychical states, some emotions stopping 
 all peristalsis. Besides their extrinsic innervation, the stom- 
 ach and intestines also contain in their walls the plexuses 
 of Meissner and Auerbach, by the action of which the peri- 
 staltic movements are believed to be co-ordinated. 
 
 The Descending Colon and Rectum and the Internal 
 Sphincter Ani. 
 
 Both the motor and the inhibitory fibers of these parts 
 arise in the spinal cord. The inhibitory fibers -of the de- 
 scending colon and rectum leave the cord in the last two 
 thoracic and the first two lumbar nerves and pass to the infe- 
 
THE GALL BLADDER AND SPLEEN. 143 
 
 rior mesenteric ganglion, from which as postganglionic fibers 
 they are distributed by way of the hypogastric nerve. The 
 motor fibers of these parts leave the cord in the nervus eri- 
 gens and reach their destination through pelvic ganglia and 
 their postganglonic branches. 
 
 The internal sphincter receives its motor fibers by way of 
 the lumbar and hypogastric nerves, and its inhibitory fibers 
 through the nervus erigens. 
 
 The fibers from the thoracic and lumbar segments are 
 most of the time in tonic activity, restraining the peristalsis 
 of the rectum and keeping its orifice closed. The sacral 
 fibers are active only occasionally and under special condi- 
 tions. 
 
 The Gall Bladder and Duct. 
 
 The gall bladder and gall duct receive efferent innervation 
 through the pneumogastric and splanchnic nerves, by way of 
 the solar and other ganglia. The pneumogastric fibers are 
 motor to the gall bladder and inhibitory to the duct, and 
 when stimulated they cause the expulsion of bile from the 
 gall bladder into the duodenum. The splanchnic fibers are 
 inhibitory to the gall bladder and motor to the duct, and the 
 combined effect, of their action is to keep the gall bladder 
 dilated and the duct contracted, thus preventing the dis- 
 charge of bile. The pneumogastric fibers are active during 
 digestion ; the splanchnic fibers are called into play when 
 digestion has ceased. 
 
 The Spleen. 
 
 The spleen is supplied through the splanchnic nerves with 
 motor fibers, the stimulation of which causes a diminution 
 in its volume, and with inhibitory fibers, the stimulation of 
 which causes dilation. These fibers are distributed to the 
 muscle-cella in the trabeculae. The conditions of their 
 activity and their normal stimuli have not been conclusively 
 determined. 
 
144 INNERVATION OF THE VISOERAL ORGANS. 
 
 ' The Bladder. 
 
 The bladder receives two sets of efferent fibers from the,, 
 spinal cord. One set leave the cord in the eleventh and 
 twelfth thoracic and the first two lumbar nerves and pass to 
 the inferior mesenteric ganglion, from which, as postgang- 
 lionic fibers, they reach the bladder by way of the hypogas- 
 tric nerve. Of these fibers those distributed to the bladder 
 walls are inhibitory and those distributed to the sphincter of 
 the bladder are motor. When stimulated the combined 
 effect of their action is to retain the bladder contents. 
 
 The other set of fibers leave the cord in the nervus erigens 
 and reach the bladder as postganglionic fibers from pelvic 
 ganglia. These fibers when stimulated have a motor effect 
 on the bladder walls and an inhibitory effect on the sphincter. 
 The combined effect of their action tends to expel the con- 
 tents of the bladder. 
 
 Both sets of fibers are normally stimulated reflexly, but 
 their activity is subject to modification under the influence of 
 impulses received from the cerebrum, through efferent tracts 
 in the spinal cord. 
 
 The Uterus. 
 
 The uterus, like the other pelvic viscera, receives two sets 
 of efferent fibers, both of which are of spinal origin. One 
 set leave the cord in the first two lumbar nerves, and pos- 
 sibly also in the last thoracic nerves, and reach the uterus as 
 postganglionic fibers from the inferior mesenteric ganglion. 
 When stimulated these fibers keep the walls of the uterus re- 
 laxed and the neck contracted — a condition that exists in 
 pregnancy. 
 
 The other set of fibers are derived through the nervus 
 erigens and pelvic ganglia. These fibers when stimulated 
 cause contraction of the walls'of the uterus and relaxation of 
 the neck. The most frequent manifestation of their activity 
 is at parturition. 
 
THE SEMINAL VESICLES. 145 
 
 The Seminal Vesicles. 
 
 Through the first two lumbar nerves and pelvic ganglia the 
 seminal vesicles receive efferent fibers, the stimulation of 
 which causes the emission of semen. These fibers are known 
 as ejaculatory nerves, and the cells from which they arise in 
 the lumbar part of the cord, as the ejaculatory center. They 
 are stimulated both reflexly and by impulses from the cere- 
 brum. 
 
INDEX. 
 
 Abducent nerve, 77 
 
 nucleus, 45 
 Accelerator center, 140 
 
 nerves, origin and effect of stimu- 
 lation of, 140 
 Accommodation reflex, 139 
 Acoustic striae, 56 
 Afferent fibers, 17, 18 
 
 tracts, spinal, 62 
 Agraphia, 37 
 Alii, 46 
 Amygdala, cerebral, 27 
 
 cerebellar, 47 
 Anterior commissure, 32 
 Aortic plexus, 125 
 Aphasia, 36 
 
 sensory, 37 
 Arachnoid of brain, 40 
 
 of spinal cord, 68 
 Arbor vitae, 47 
 Areuate fibers, 53 
 Areas of cerebral cortex, 35- 
 Arm, nerves of, 96 
 Arterial pressure, regulation of, 134 
 Association areas in brain, 37 
 
 fibers in brain, 33 
 
 tracts in spinal cord, 64 • 
 Atrophy of nerve, 22 
 Auditory area, 36 
 
 speech area, 36 
 
 nerve, course of, in brain, 55 
 Augmentation of heart beat, 140 
 
 ot reflexes, 66 
 Automatic activity of respiratory 
 
 center, 111 
 Axis-cylinder, 14 
 Axon, 14 
 
 BlPOLAB cells, 15 
 
 Bladder, nerves of, 133, 144 
 
 Blood-vessels, innervation of, 128 
 
 Bodies, geniculate, 43 
 
 restiform, 51 
 
 quadrigeminal, 42 
 Body-sense area, 35 
 Brachial plexus, formation of, 96 
 
 lateral branches of, 96 
 Brachium, anterior, 43 
 
 posterior, 43 
 Brain sand, 40 
 Broca's convolution, 36 
 Bronchi, nerves of, 149 
 Bundle, Cajal's descending cerebel- 
 lar, 48 
 
 inferior longitudinal, 33 
 
 posterior longitudinal, 42 
 
 superior longitudinal, 33 
 
 of Vicq-d'Azyr, 34 
 Burd^ch, tract of, 62 
 
 Cactjmen, 46 
 
 Cajal's descending cerebellar bundle, 
 
 48 
 Calamus scriptorius, 51 
 Capsule, external, 32 
 
 internal, 31 
 Cardiac plgxus, 125 
 
 nerves, 140 
 Cardio-inhibitory center, 53, 140 
 Cauda equina, 68 
 Caudate nucleus, 27 
 Center or centers, accelerator, 140 
 
 cardio-inhibitory, 53 
 
 cilio-spinal, 140 
 
 ejaculatory, 145 
 
 memory, 37 
 
 respiratory, 53 
 
 vasoconstrictor, 53 
 Cerebellum, 46 
 
 cortex, histology of, 47 
 
 peduncles of, 44, 48, 63 
 
 physiology of, 48 
 
 (147) 
 
148 
 
 INDEX. 
 
 Cerebro-spinal fluid, 40 
 Cerebrum, 25 
 
 cortex, histology of, 26 
 
 gray matter of, 25 
 
 physiology of, 35 
 
 surfaces of, a8 
 Cervical plexus, formation of, 71 
 
 distribution of, 83, 94 
 Chiasm, optic, 78 
 Chorda tympani nerve, 87, 124 
 Chromatolysis, 14 
 Chromophile material, 14 
 Ciliary ganglion, 123 
 Ciliary muscle, nerves of, 138 
 Cilio-spinal center, 138 
 Clarke, column of, 63 
 Claustrum, 27 
 Clava, 51 
 
 Clitoris, nerve of, 108 
 Clivus, 46 
 
 Colon, nerves of, 132, 142 
 Columns of spinal cord, 60 
 Comma tract, 62 
 Commissure, anterior, 32 
 
 gray, 60 
 
 middle, 35 
 
 posterior, 35 
 
 vphite, 60 
 Conduction, crossed, in spinal cord, 64 
 Conductivity, 19 
 Convolutions of cerebrum, angular, 29 
 
 callosal, 30 
 
 cuneus, 30 
 
 frontal, 29, 30 
 
 hippooampal, 31 
 
 occipital, 29 
 
 para-central, 30 
 
 post-central, 29 
 
 pre-central, 29 
 
 pre-cuneus, 30 
 
 suboalcarine, 31 
 
 subcoUateral, 31 
 
 superior parietal, 29 
 
 supra-marginal, 29 
 
 temporal, 29 
 Corona radiata, 31 
 Corpora albicantia, 35 
 
 genioulata, 43 
 
 quadrigemina, 42 
 Corpus albicans, 34 
 
 callosum, structure and function 
 of, 32 
 
 Corpus mammillare, 34 
 
 trapezoideum, 44 
 Cortex of cerebrum, 26 
 
 of cerebellum, 47 
 Coughing, 113 
 Cranial nerves, general functions of, 
 
 73 
 Crossing of fillets, 52 
 Crura cerebri, 41 
 Crusta, 41 
 Culmen, 46 
 
 Decussation, pyramidal, 50 
 
 sensory, 52 
 Degeneration of nerve, 21 
 Deiters' nucleus, 56 
 Dendrites, 14 
 Dentate nucleus, 53 
 Depressor nerves, 134 
 Diaphragm, nerves of, 109 
 Dilator-pupillae, function of, 138 
 
 nerves of, 138 
 Dura of brain, 39 
 
 of spinal cord, 68 
 
 Efferent fibers, function of, 17 
 
 classes of, 17 
 Ejaculatory center, 145 
 
 nerves, 145 
 Embryonic fiber, 21 
 Eudoneurium, 16 
 Epineurium, 16 
 Epiphysis, 35 
 Expiratory center. 111 
 
 muscles, action of. 111 
 
 nerves, 110 
 External capsute, 32 
 External genital organs, nerves of, 
 
 107 
 External parts of head, nerves of, 
 
 81 
 
 Facial nerve, 84 
 
 afferent root of, 57 
 
 distribution of, 84, 87 
 
 functions of, 73 
 
 ganglion of, 87 
 
 nuclei, 45, 57 
 Ealx oerebelli, 40 
 
 cerebri, 40 
 Fasciculus cuneatus, 51 
 I gracilis, 51 
 
INDEX. 
 
 149 
 
 Fasciculus of Eolaudo, 51 
 
 solitarius, 57 
 Fillet, 54 
 
 Filum terminale, 59 
 Fimbria, 34 
 Fissure, anterior median, 50, 59 
 
 an/tero-lateral, 50 
 
 calcarine, 30 
 
 calloso-marginal, 30 
 
 central, 28 
 
 circular, 31 
 
 collateral, 31 
 
 longitudinal, 25 
 
 parieto-occipital, 28 
 
 posterior median, 59 
 
 postero-lateral, 59 
 
 pre-eentral, 29 
 
 transverse, 46 
 Flectsig, tract of, 63 
 FIbeeulus, 47 
 Folia, 46 
 Foramen of Key and Betzius, 54 
 
 of Munro, 34 
 Forceps anterior, 32 
 
 posterior, 32 
 Formatio reticularis, 42 
 Fornix, 33 
 Frenulum, 46 
 Frontal lobe, on lower surface, 30 
 
 on mesial surface, 30 
 
 on outer surface, 28 
 Funiculus, 16 
 
 Gall bladder, nerves of, 132, 143 
 Ganglia, classes of, 13 
 
 of head region, 123 
 
 lumbar, 122 
 
 sacral, 122 
 
 structure of, 13 
 
 thoracic, 121 
 
 vertebral, 118 
 Ganglion, aortico-renal, 125 
 
 ciliary, 123 
 
 Gasserian, 75 
 
 geniculate, 87 
 
 impar, 122 
 
 inferior cervical, 120 
 
 inferior mesenteric, 126 
 
 jugular, 86 
 
 middle cervical,,, 120 
 
 ftio, 123 
 
 petrosal, 86 
 
 Ganglion, root-, 90 
 
 semi-lunar, 125 
 
 spheno-palatine, 123 
 
 spiral, 88 ' 
 
 sublingual, 124 
 
 submaxillary, 124 
 
 superior cervical, 119 
 
 superior mesenteric, 125 
 
 trunk-, 90 
 
 vestibular, 88 
 
 of Wrisberg, 125 
 Genu of internal capsule, 31 ^ 
 
 of callosum, 32 
 Glosso-pharyngeal nerve, 86 
 
 distribution of, 87 
 
 ganglia of, 86 
 
 nuclei of, 86 
 
 roots of, 86 
 Great superficial petrosal nerve, 123 
 Golgi cells, 16 
 Gon, tract of, 62 
 Gowers, tract .of, 63 
 Gudden 's commissure, 43 
 Gustatory area, 36 
 
 nerves, 86, 87 
 
 Heart, nerves of, 138 
 Hemorrhoidal plexus, 126 
 Hepatic plexus, 125 
 Hiccoughing, 113 
 Hip, nerves of, 102 
 Hypogastric plexus, 126 
 Hypoglossal nerve, 86 
 
 nucleus, 53 
 Hypophysis, 35 
 
 Inpeeiok cervical ganglion, 120 
 Inferior olive, 50 
 Inhibition of heart, 140 
 
 of reflexes, 65 
 
 of respiration, 112 
 Inhibitory fibers, function of, 18 
 Inspiratory center. 111 
 
 muscles, action of, 110 
 
 nerves, 109 
 Insula, 31 
 Internal capsule, 31 
 Internal parts of ear, nerves of, 88 
 Internodes, 15 
 Iris, nerves of, 138 
 Island of EeU, 31 
 Isthmus cerebri, 41 
 
150 
 
 INDEX. 
 
 Key and Betzius, foramen of, 54 
 Kidneys, vaso-motor nerves of, 132 
 Kjiee-jerk, 67 
 
 Lamina quadrigemina, 42 
 
 Larynx, nerves of, 90 
 
 Lateral column of spinal cord, 60 
 
 fillet, 54 
 
 nucleus, 52 
 Laughing, 113 
 Leg, nerves of, 102 
 Leinnisous, 44 
 Lenticular nucleus, 27 
 Ligamentum denticulatum, 68 
 Limbic lobe, 30 
 Lingula, 46 
 Lobe, anterior cresoentie, 46 
 
 central, 46 
 
 digastric, 47 
 
 frontal, 29 
 
 limbic, 30 
 
 occipital, 29, 30 
 
 parietal, 29, 30 
 
 posterior crescentio, 46 
 
 postero-inferior, 47 
 
 postero-superior, 46 
 
 slender, 47 
 
 temporal, 29, 30 
 Lumbar ganglia, 122 
 
 nerves, 72 
 
 plexus, 72, 102 
 Lyra, 34 
 
 Mandibtjlak division of fifth nerve, 
 
 82 
 Maxillary division of fifth nerve, 76 
 Median nerve, 101 
 Membranes of brain, 39 
 
 of spinal cord, 68 
 Memory, cortical centers for, 36 
 Metatela, 54 
 
 Micturition, inhibition of, 65 
 Midbrain, 41 
 Miotics, 139 
 Motor aphasia, 36 
 
 area, 35 
 
 speech area, 36 
 
 fibers, 17 
 
 paths in spinal cord, 60 
 Mouth, nerves of, 85 
 Multipolar cells, 16 
 Muscle-sense, 38 
 
 Muscle-sense, cortical area for, 35 
 
 paths for, in spinal cord, 60 
 Mydriatics, 139 
 
 N/SAL fossae, nerves of, 79 
 
 Nates, 42 
 
 Neck, nerves of, 94 
 
 vaso-motor nerves of, 129 
 Nerve or nerves, abducent, 77 
 ansa hypoglossi, 95 
 anterior crural, 102 
 of Arnold, 84 
 auditory, 88 
 auriculo-temporal, 83 
 buccal, long, 82 
 caloaneo-plantar, 105 
 oerviealis descendens, 95 
 chorda tympani, 87 
 ciliary, long, 76 
 
 short, 76 
 circumflex, 98 
 cutaneous, descending, of neck, .9 
 
 dorsal, of arm, 100 
 
 external, of arm, 99 
 
 external, of leg, 102 
 
 internal, of arm, 99 
 
 internal, of leg, 103 
 
 palmar, 101 
 
 perforating, 104 
 
 small internal, 99 
 deep temporal, 82 
 
 petrosal, great, 120 
 
 small, 120 
 depressor, 134 
 descendens hypoglossi, 95 
 dorsal, of penis, 108 
 facial, 84 
 
 fibular communicating, 104 
 frontal, 75 
 genito-crural, 102 
 glosso-pharyngeal, 86 
 gluteal, inferior, 104 
 
 superior, 103 
 great auricular, 83 
 hypoglossal, 86 
 ilio-inguinal, 102 
 ilio-hypogastric, 102 
 inferior dental, 86 
 inferior palpebral, 77 
 infra-mandibular, 94 
 infra-orbital, 84 
 infra-trochlear, 76, 81 
 
INDEX. 
 
 161 
 
 Nerve or nerves, intercostal, 71 
 internal pterygoid, 82 
 interosseous, anterior, 101 
 
 posterior, 98 
 lachrymal, 75 
 lateral nasal, 82 
 lingual, of fifth, 86 
 
 of ninth, 86 
 laryngeal, superior, 92 
 
 inferior or recurrent, 92 
 masseteric, 82 
 malar, 84 
 median, 101 
 musculo-cutaneoua, of arm, 99 
 
 of leg, 105 
 musculo-spiral, 98 
 mylohyoid, 94 
 nasal, 76 
 
 naso-palatine, 79, 85 
 nervus erigens, 122 
 obturator, 103 
 occipital, great, 83 
 
 small, 83 
 
 third, 83 
 oeulo-motor, 77 
 olfactory, 80 
 optic, 78 
 palatine, anterior, 85 
 
 external, 91 
 
 posterior, 91 
 perineal, 107 
 peroneal, 105 
 phrenic, 109 
 plantar, 105 
 phaj^rngeal, of fifth, 91 
 
 of ninth, 92 
 
 of tenth, 92 
 pneumogastrio, 90 
 posterior auricular, 84 
 popliteal, 104 
 pudendal, inferior, 107 
 
 long, 104 
 pudic, 107 
 radial, 98 
 rhomboid, 96 
 saphenous, internal, 103 
 
 short, 104 
 sciatic, great, 104 
 
 small, 104 
 spinal accessory, 91 
 splanchnic, 121 
 stylohyoid, 94 
 
 Nerve or nerves, subclavian, 97 
 
 subscapular, 97 
 
 superficial cervical, 95 
 
 superficial petrosal, 123 
 
 superior dental, 85 
 
 superior labial, 82 
 
 superior nasal, 79 
 
 supra-orbital, 81 
 
 supra-scapular, 97 
 
 supra-mandibular, 84 
 
 supra-trochlear, 81 
 
 temporal, 82 
 
 temporo-malar, 81 
 
 thoracic, external anterior, 97 
 internal anterior, 97 
 posterior, 97 
 
 tibial, anterior, 106 
 posterior, 105 
 
 tibial communicating, 104 
 
 tonsillar, 92 
 
 trifacial, mandibular division, 82 
 maxillary division, 76 
 ophthalmic division, 75 
 
 trochlear, 77 
 
 tympanic, 88 
 
 ulnar, 100 
 Nerve-ceUs, structure of, 14 
 
 varieties of, 15 
 Nerve-fibers, histology of, 15 
 
 functional classes of, 17 
 Nerve-tissue, 13 
 Nerve impulses, 20 
 
 stimuli, 19 
 Nervi nervorum, 17 
 Nervus erigens, formation and 
 
 functions of, 122 
 Nervous system, parts of, 13 
 Neurilemma, 15 
 Neurofibrils, 14 
 Neuroglia, 13 
 Neuron, structure of, 14 
 Nisl's granules, 14 
 Nodes of Ranvier, 15 
 Nodule, 47 
 Nucleus or nuclei, abducent, 45 
 
 accessory, 55 
 
 ambiguus, 53 
 
 auditory, 55 
 
 of Bechterew, 56 
 
 caudate, 27 
 
 cuneatus, 53 
 
 of Deiters, 56 
 
152 
 
 iNhEX. 
 
 Nucleus or nuclei, dentate, 47, 53 
 
 facial, 45 
 
 gracilis, 53 
 
 hypoglossal, 53 
 
 lateral, 52 
 
 lenticular, 27 
 
 oculo-motor, 42 
 
 olfactory, 80 
 
 oliyary, 45 
 
 optic, 55 
 
 posterior, 56 
 
 red, 42 
 
 sensory, of seventh, ninth and 
 tenth nerves, 53 
 
 trapezoidal, 45 
 
 trifacial, 42, 45 
 
 trochlear, 42 
 Nuclei gracilis and cuneatus, dis- 
 tribution of fibers of, 53 
 
 Oblongata, 50 
 
 internal structure of, 51 
 
 gray matter. of, 58 
 
 surfaces of, 50, 51 
 Occipital lobe, 29, 30 
 Oculo-motor nerve, 77 
 
 nucleus, 42 
 Oesophagus, nerves of, 141 
 Olfactory area, 35 
 
 bulb, 80 
 
 end-organ, 80 
 
 fissure, 80 
 
 groove, 80 
 
 nerve, 80 
 
 nucleus, 80 
 Ophthalmic division of fifth nerve, 
 
 75 
 Optic Chiasm, 78 
 
 nerve, 78 
 
 nuclei, 55 
 
 radiation, 55 
 
 tracts, 78 
 Optic thalamus, structure of, 27 
 Otic ganglion, 123 
 Ovaries, vaso-motor nerves of, 133 
 
 Pacchionian bodies, 40 
 
 Pain sense, distribution of fibers 
 
 of, 38 
 Pars intermedia, 57 
 Parietal lobe, 29, 30 
 Peduncles, cerebellar, inferior, 63 
 
 Peduncles, middle, 44 
 
 superior, 48 
 Pelvic plexus, 126 
 Penis, nerves of, 108 
 Perineum, nerves of, 107 
 Perineurium, 16 
 Petrosal nerve, great superficial, 123 
 
 small superficial, 124 
 Pharyngeal plexus, 93 
 Pharynx, nerves of, 90 
 Phrenic nerve, 109 
 Pia of brain, 39 
 
 of spinal cord, 68 
 Plexus or plexuses, aortic, 125 
 
 brachial, 96 
 
 cardiac, 125 
 
 carotid, 120 
 
 cavernous, 120 
 
 coccygeal, 108 
 
 coronary, 125 
 
 hemorrhoidal, 126 
 
 hepatic, 125 
 
 hypogastric, 126 
 
 inferior mesenteric, 126 
 
 lumbar, 102 
 
 of Meissner and Auerbach, 117 
 
 oesophageal, 90 
 
 patellar, 103 
 
 pelvic, 126 
 
 pharyngeal, 93 
 
 phrenic, 125 
 
 prostatic, 127 
 
 pulmonary, 125 
 
 renal, 126 
 
 sacral, 103 
 
 solar, 125 
 
 splenic, 125 
 
 subsartorial, 103 
 
 subtrapezial, 94 
 
 superior mesenteric, 125 
 
 supra-renal, 126 
 
 tympanic, 88 
 
 uterine, 127 
 
 vaginal, 127 
 
 vesical, 126 
 Pneumogastrio nerve, 90 
 
 functions of, 73 
 
 nuclei, 53 
 Pons, structure of, 44 
 Porta, 34 
 Posterior longitudinal bundle, 42 
 
 columns of spinal cord, 60 
 
INDEX. 
 
 15S 
 
 Postganglionie fibers, 117 
 
 Preganglionic fibers, 117 
 
 Pressor nerves, 134 
 
 Pressure sense, distribution of fibers 
 
 of, 38 
 Prevertebral plexuses, 125 
 Processes, axis-cylinder, 14 
 
 dendritic, 14 
 Projection fibers, 33 
 Prostatic plexus, 127 
 Pulmonary plexuses, 125 
 Pulvinar, 28 
 
 Pupillo-constrictor nerves, 138 
 Pupillo-dilator nerves, 138 
 Purkinje cells, 47 
 
 fibers of, 48 
 Pyramid or pyramids, cerebellar, 47 
 
 of oblongata, 50 
 Pyramidal cells, 26 
 
 decussation, 52 
 
 tracts, 60 
 
 Rami communioantes, 118- 
 
 efferentes, 118 
 Eaphe, 41 
 
 Eectum, nerves of, 142 
 Reflex action, 64 
 Reflexes, augmentation of, 66 
 
 classification of, 65 
 
 inhibition of, 65 
 
 influence of condition of nerve- 
 centers on, 66 
 Regeneration of nerve, 21 
 Renal plexus, 126 
 
 Respiratory center, functions and 
 properties of, 111 
 
 mechanisms, nerves of, 109 
 
 movements, modification of, 112 
 Restiform body, 51 
 Rostrum, 32 
 Eubro -spinal tract, 61 
 
 Sacral ganglia, 122 
 
 plexus, formation of, 72 
 
 branches of, 103 
 Scrotum, nerves of, 108 
 Secretory fibers, 18 
 Seminal vesicles, nerves of, 145 
 Senses, classification of, 37 
 
 peripheral fibers of, 38 
 Sense-organ, 37 
 Sensory aphasia, 36, 37 
 
 Sensory areas, 35 
 
 decussation, 52 
 
 nerves, 19 
 
 paths in spinal cord, 62 
 Septum lucidum, 34 
 Sheath of Henle, 17 
 
 medullary, 14 
 
 primitive, 14 
 Shoulder, nerves of, 96 
 Sighing, 113 
 
 Small intestine, nerves of, 132, 142 
 Sneezing, 113 
 Sobbing, 113 
 
 Soft palate, nerves of, 90 
 Solar plexus, 125 
 Space, interpeduncular, 41 
 
 anterior perforated, 80 
 Spheno-palatine ganglion, 123 
 Sphincter ani, nerves of, 142 
 Spinal accessory nerve, 91 
 
 functions of, 73 
 Spinal cord, structure of, 59 
 
 afferent tracts in, 62 
 
 association tracts in, 64 
 
 efferent tracts in, 60 
 
 membranes, 68 
 
 nerve-roots, 67 
 
 nerves, general distribution of, 71 
 Splanchnic nerves, 121 
 Spleen, nerves of, 143 
 Splenium, 32 
 
 Stomach, nerves of, 132, 142 
 Striae longitudinales, 33 
 Subdural cavity, 40 
 Sublingual ganglion, 124 
 
 gland, nerves of, 129 
 Submaxillary ganglion, 124 
 
 gland, nerves of, 129 
 Substantia gelatinosa, 51, 59 
 
 nigra, 41 
 Superior cervical ganglion, 119 
 Supra-renal bodies, nerves of, 132 
 
 plexus, 126 
 Sympathetic nervous system, for- 
 mation of, 117 
 
 Taenia semicircularis, 27 
 Tapetum, 33 
 Taste, nerves of, 86, 87 
 Teeth, nerves of, 85, 86 
 Tegmentum, 42, 44 
 Temperature sense, distribution of 
 fibers of, 38 
 
154 
 
 INDEX. 
 
 Temporal lobe, 29, 30 
 Tentorium, 31, 40 
 Testes, 42 
 
 Thalamus, optic, 27 
 Thirst, sense of, 39 
 Thoracic ganglia, 121 
 
 nerves, distribution of, 71 
 Tone, arterial, maintenance of, 134 
 Tongue, nerves of, 86, 87 
 Tonsils, nerves of, 90 
 Touch, .sense of, 38 
 Tract, anterior marginal, 62 
 
 antero-lateral ascending, 63 
 
 of Burdach, 62 
 
 comma, 62 
 
 direct cerebellar, 63 
 
 of Flechsig, 63 
 
 of Goll, 62 
 
 of Gowers, 63 
 
 Helweg 's, 62 
 
 of Lissauer, 62 
 
 optic, 78 
 
 pyramidal, 60 
 
 rubro-spinal, 61 
 
 sulco-marginal, 61 
 
 vestibulo-spinal, 61 
 Trapezium of pons, 44 
 
 of cerebellum, 47 
 Trifacial nerve, afferent root of, 56 
 
 efferent root of, 82 
 
 ganglion of, 75 
 
 first division of, 75 
 
 second division of, 76 
 
 third division of, 82 
 Trochlear nerve, 77 
 
 nucleus, 42 
 Trophic fibers, 18 
 Tuber annulare, 44 
 Tubercle, anterior, 28 
 
 of Eolando, 51 
 Tuberculum acusticum, 55 
 
 Uncinate bundle, 33 
 Uterine plexus, 127 
 Uterus, nerves of, 144 
 Uvula, cerebellar, 47 
 
 Vagina, nerves of, 127, 133 
 
 Vaginal plexus, 127 
 Vagus nerve, see 
 
 nerve 
 Valvula, 45 
 
 Vaso-constrictor center, function of, 
 134 
 
 modification of activity of, 135 
 
 nerves, function of, 134 
 independent action of, 136 
 origin of, 128 
 Vaso-dilator nerves, function of, 137 
 
 modification of activity of, 137 
 
 origin of, 128 
 Vaso-motor nerves of abdominal 
 organs, 132 
 
 of bladder, 133 
 
 of brain, 131 
 
 of genital organs, external, 133 
 internal, 133 
 
 of head region, 128 
 
 of larynx, 130 
 
 of Umbs, 129 
 
 of lungs, 181 
 
 of neck, 129 
 
 of pharynx, 130 
 
 of rectum, 132 
 
 of sigmoid colon, 132 
 
 of spinal cord, 130 
 
 of tonsils, 130 
 
 of trunk, 129 
 Velum interpositum, 89 
 
 aniterior medullary, 45 
 Ventricle, lateral, 34 
 
 third, 34 
 
 fourth, 54 
 Vesical plexus, 126 
 Vestibulo-spinal tract, 61 
 Vic-d'Azyr, bundle of, 84 
 Vieussens, valve of, 45 
 Visual area, 86 
 
 speech area, 36 
 
 White commissure, 60 
 "Word-blindness, 37 
 
 deafness, 36 
 Wrisberg, ganglion of, 125 
 Writing area, 37 
 
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