THE LIBRARY 
 
 OF 
 
 THE UNIVERSITY 
 OF CALIFORNIA 
 
 PRESENTED BY 
 
 PROF. CHARLES A. KOFOID AND 
 MRS. PRUDENCE W. KOFOID 
 
LECTURE NOTES ON 
 PHYSIOLOGY 
 
 BY 
 HENRY H. JANEWAY, M.D. 
 
 THE NERVOUS SYSTEM 
 
 NEW YORK 
 
 PAUL B. HOEBER 
 67-69 EAST SQTH STREET 
 
Copyright, 1915, 
 BY PAUL B. HOEBEK 
 
 Reprinted October, 1917, and , 1918 
 
M371676 
 
I 
 THE NERVES 
 
 THE PERIPHERAL NERVES 
 
 STRUCTURAL BASIS OF THE NERVOUS SYSTEM 
 
 The Purpose Served by the Nervous System The nervous 
 system has developed in order that a rapid communication be- 
 tween the distant portions Of the body may be possible. Its tis- 
 sues in the process of specialization of function have acquired the 
 highest perfection of the vital phenomena of excitability and of the 
 power of transmission of a change dependent on excitement. 
 Among unicellular animals special provision for such a means of 
 communication does not exist. Among the metazoa, i.e., the sponges, 
 no evidence of a nervous system exists. It is in the Coelenterata 
 
 that the first evidences of a nervous system are met with. 
 
 i 
 
 DEVELOPMENT OF THE NERVOUS SYSTEM 
 
 The Hydra In the hydra some of the epithelial cells have pro- 
 longations which join or, at least, come into contact with deeper 
 cells possessing special contractile power. (Fig. 1.) We can imag- 
 ine that these epithelial cells with their prolongations have become 
 endowed with a special sensitiveness to external irritants, and pos- 
 sess the power of quickly transmitting the effects of the external 
 changes upon it to the contractile cells and in a manner to cause the 
 latter to respond immediately. 
 
 Ccelenterates The jelly fish presents quite an advance over this 
 simple nervous system and no intermediate stages are known. 
 (Fig. 2.) The nervous system of the jelly fish is limited to the 
 region beneath the margin of the umbrella. From the epithelium 
 of the surface, fibers pass inward forming a network around the 
 margins of the umbrella. In this network there are thickenings 
 in which are situated nerve cells. (Fig. 3.) A finer network of 
 
 4 
 
THE NERVOUS SYSTEM 
 
 Fig. 1. Diagrammatic illustration of the evolution of the reflex arc. 
 A shows a single cell differentiated into a conductive (1), and contractile 
 portion (2). In B the conductive portion (1) and the contractile portion (2) 
 exist a$ separate cells and maintain their connection with the sensory element 
 by a slender conductive portion in this cell, which represents a nerve (3). 
 In C the sensory cell (1) and the contractile element are separate cells, but 
 the connection between the two is maintained by an interpolation of a new 
 nerve cell receiving an afferent extension (3) from the sensory cells and 
 giving off an efferent extension (5) of the muscle cell. 
 
 fibers originates in the network just described and terminates 
 around muscular cells (cells, in other words, which have acquired in 
 the process of specialization the highest perfection for that in- 
 dividual animal of the vital phenomenon of contraction). Be- 
 sides these two sets of nerve fibers, another set of fibers containing 
 small collections of cells also exists beneath the Tnargins of the 
 umbrella. 
 
THE NERVOUS SYSTEM 
 
 The various sensitive cells on the surface present differences in 
 their capabilities of responding to various stimuli. Such differ- 
 ences represent specialization of the function of excitability. Some 
 are more sensitive to light, others to the weight of a crystal of lime 
 developed near them, and still others to chemical and contact stim- 
 
 TENTACL.ES 
 
 Fig. 2. Diagram of a jelly fish. 
 In this organism the central nervous cells are peripherally placed. 
 
 uli. By cutting off the marginal ring with its marginal bodies we 
 will remove the special sense organs and the ganglion cells of the 
 umbrella. Such a mutilated jelly fish lies perfectly motionless in 
 the water. It is incapable of any automatic activity because de- 
 prived of cells sensitive to external changes its muscle cells receive 
 no stimuli. If a stimulus is applied to the cut nerve's running to 
 
 8 
 
THE NERVOUS SYSTEM 
 
 the contractile cells within, the jelly fish will contract. Under 
 
 these conditions the manubrium will bend in the direction of the 
 
 stimulus. 
 
 A more Advanced Stage with Centrally placed Ganglion Cells 
 - In the jelly fish the ganglion cells, which we may term perhaps 
 
 switch stations or relay stations, are sit- 
 - uated around the periphery of the body. 
 It will be a manifest advantage to an 
 animal to have these switch stations sit- 
 uated centrally. Animals with cen- 
 trally situated stations, such as the 
 worms, represent the next stage in the de- 
 velopment of a nervous system. (Fig. 4.) 
 The Crayfish A still further ad- 
 vance is represented in animals such as 
 the crayfish, in which the head ganglia, 
 those in the direction in which the ani- 
 mal moves forward, show a special de- 
 velopment. 
 
 In these animals we have the rudi- 
 ments of projicient sense organs, organs 
 furnishing the animal with information 
 of what is in the course of its advance. 
 They may be not improperly termed or- 
 gans of foresight. Through the con- 
 necting strands of fibers between these 
 anterior organs and the ganglia behind 
 them impulses may be sent to check for- 
 ward movement when danger ahead is 
 scented. These impulses are the begin- 
 nings of inhibitory impulses. In all 
 these primitive forms of nervous sys- 
 tems, as in the jelly fish, the nervous 
 
 system starts its development from the surface epithelial cells. 
 The Sensory Cell The differentiated peripheral sensory cell 
 
 possesses two processes a short one passing to the surface, and a 
 
 long one passing back to intermingle with a network of fibers in the 
 
 interior of the animal. (Fig. 5.) 
 
 The Central Ganglion This network also contains ganglion 
 
 10 
 
 Fig. 3. Illustrating the com- 
 munications between the 
 muscle (1) on one side of 
 the umbrella and the sen- 
 sory epithelium (2) upon 
 the other side through the 
 peripherally placed cells 
 (3). 
 
THE NERVOUS SYSTEM 
 
 Fig. 4. Illustrating the stages in the evolution of a centrally placed nerve cell. 
 
 In 1 direct communication between the muscle and sensory cell. 
 
 In 2 indirect communication between the sensory cell and the muscle 
 through a peripherally placed nerve cell. 
 
 In 3 indirect communication between the sensory cell and the muscle 
 through a centrally placed nerve cell. 
 
 cells, the processes of which also intermingle with terminal divisions 
 of the processes of the differentiated surface epithelial cells. The 
 intermingling of the fibers forms a network embedded in a granular 
 substance more or less encapsulated and forming a ganglion. 
 While many of the fibers of the ganglion cells participate in the 
 
 Lumbricus 
 
 Nereis 
 
 Vertebrate 
 
 Fig. 5. Diagrams showing the relative position of the sensory cell in lum- 
 bricus, nereis, and vertebrata. (Quain.) 
 
 12 
 
THE NERVOUS SYSTEM 
 
 formation of the network, one long process from some of the gan- 
 glion cells passes to a muscle cell of the animal. It is believed that 
 some divisions of the long fibers from the differentiated sensitive 
 epithelial cell may become a part of the central ganglion cell and 
 pass directly through it. If this occurs it is exceptional, but it is 
 significant that some fibers of the terminal network from the differ- 
 entiated sensitive epithelial cell may pass directly into a fiber run- 
 ning to a muscle without at any time becoming a part of a central 
 
 Fig. 6. Transverse section of a human embryo of 24 mm. (Quain.) 
 ent, entoderm of yolk-sac; the lines indicate the points of the splanchno- 
 pleuric layers which will come together to cut off the gut from the cavity of 
 the yolk-sac; my, outer wall of mesodermic segment; me, the part of its wall 
 which forms the muscle-plate; sc, sclerotome; coe, ccelom. 
 
 nerve cell. This primitive system is thus composed of two ele- 
 ments the receiving element, which is the differentiated sensitive 
 epithelial cell with its short and long process, and the reactive ele- 
 ment, or the peripherally running nerve to the muscle, which may 
 or may not arise in a central nerve cell. The one is called the sen- 
 sory or afferent neuron and the other the motor or efferent neuron. 
 
 The Embryological Development of the Nervous System of the 
 Vertebrates The nervous system of vertebrates is developed from 
 the epithelium of a groove which forms upon the dorsum of the 
 embryo. This groove -subsequently becomes transformed into a 
 canal. At the front end three cavities become formed from which 
 the three brains develop. From the greater length of the canal 
 posteriorly the spinal cord forms. (Figs. 6-9.) 
 
 The Spongioblasts and Neuroblasts 'The canal is formed of 
 
 14 
 
THE NERVOUS SYSTEM 
 
 columnar cells between the outer ends of which small rounded cells 
 are found. From the columnar cells, called spongioblasts, is formed 
 the neuroglia by the production of branching processes. Many of 
 the columnar cells wander externally and become transformed into 
 round cells with many branches. These branches form the sup- 
 porting network of the nervous system, the neuroglia. (Figs. 10- 
 
 Yolk-sac. 
 
 Amnion. 
 
 Neural groove. 
 
 Neurenteric canal. ' ~ 
 
 Primitive streak. 
 Abdominal stalk. 
 
 Fig. 7. Surface view of early human embryo, 2 mm. in length (after Graf. v. 
 
 Spec.) x 30 diameters. (Quain.) 
 
 The amnion is opened, and on the blastoderm are seen the primitive 
 streak, the dorsal opening of the neurenteric canal, and the neural groove. 
 
 13.) The round cells appearing in the intervals between the outer 
 ends of the columnar cells 'are termed neuroblasts. 
 
 The Development of the Sensory and Motor Nerve Fibers - 
 From the neuroblasts grow out a process which at first has a bulb- 
 shaped extremity. (Fig. 15.) By continued growth of the process 
 finally reaches the periphery, to end in a muscle or gland. (Figs. 
 14, 15.) This process is called the axis cylinder of the nerve cell. 
 After the growth of the axis cylinder is well advanced other proc- 
 esses grow out from the cell and terminate ultimately in a series of 
 
 16 
 
THE NERVOUS SYSTEM 
 
 branches called dendrites. These cells constitute the efferent path 
 of the central nervous system. The afferent path develops from 
 cells formed outside the primitive neural groove from cells which 
 
 n. f. n. gr. n. f. 
 
 mes. 1 
 
 n. f. 
 
 Ill 
 
 Fig. 8. Transverse sections of the human embryo of 2 mm. represented in 
 
 Fig. 7. (Quain.) 
 
 In I, which is most anterior, the fore-gut is separated off from the yolk-sac. 
 n. gr., neural groove; n. /., neural folds; n. pi. (in III), neural plate; mes. 1 , 
 intra-embryonic mesoderm; p., pericardial crelom; am.ect., amniotic ecto- 
 derm; mes. 2 , amniotic mesoderm; ent., entoderm of yolk-sac; mes?, meso- 
 derm of yolk-sac; not.pl. (in III), notochord-plate. 
 
 form a longitudinal thickening just external to the latter. From 
 these cells two processes grow out, one from each pole. (Figs. 17- 
 20.) The peripheral one grows to the surface to terminate in a 
 sentient epithelial cell. The central one grows internally into the 
 
 18 
 
THE NERVOUS SYSTEM 
 
 
 Fig. 9. Closure of neural canal of human embryo, showing the cells of the 
 neural crest becoming separated to form the germs 
 
 of the spinal ganglia. (Quain.) 
 A, canal still open; B, canal closed. 
 
 Fig. 10. Neuroglia cells and fibres from the white matter of the human 
 cerebellum stained by Weigert's neuroglia stain. A, Neuroglia cell; B, 
 blood-vessel cut longitudinally, and C, blood-vessel cut transversely, show- 
 ing enveloping neuroglia fibres; a, neuroglia fibres; b, cytoplasm of neu- 
 roglia cell. (Bailey.) 
 
 20 
 
THE NERVOUS SYSTEM 
 
 Fig. 11. A, Neuroglia cell spider type human cerebrum. B, Neuroglia 
 cell mossy type human cerebrum. (Bailey.) 
 
 Fig. 12. Neuroglia-cells of cerebellum. Golgi method. (Quain.) 
 a, spider-cells; b, arborescent cells; c, ependyma-like cells. 
 
 22 
 
THE NERVOUS SYSTEM 
 
 Fig. 13. A neuroglia-cell, isolated in 33 per cent, alcohol. (Quain 
 
 Fig. 14. A, ventral root-fibres; B, dorsal root-fibres; C, a neuroblast be- 
 ginning to bud out; D, a neuroblast with long fibre passing towards ven- 
 tral commissure; E, a motor neuroblast with axon and dendrons; F, a 
 motor neuroblast with axon only: the axon is expanded at the growing 
 end; a, a, neuroblasts with axons growing into the lateral column; c, grow- 
 ing end of axon of a commissural fibre; d, a cell of the spinal ganglion. 
 (Quain.) 
 
 24 
 
THE NERVOUS SYSTEM 
 
 A 
 
 Fig. 15. Neuroblasts from the spinal cord of a third-day chick-embryo. 
 
 (Quain.) 
 
 A, three neuroblasts, stained by Cajal's reduced-silver method, showing a 
 network of neurofibrils in the cell-body; a, a bipolar cell. B, a neuroblast 
 stained by the method of Golgi showing the incremental cone (c). 
 
 a be 
 
 Fig. 16. Section of wall of neural tube (first cerebral vesicle) of chick of 
 
 three and a half days. (Quain.) 
 
 A, germinal layer containing rounded neuroblasts, a, b, c (these already 
 possess fibrils); B, bipolar neuroblasts; c, enlarged growing end of axon; 
 e, an axon growing tangentially. 
 
 26 
 
THE NERVOUS SYSTEM 
 
 Fig. 17-A. Chick-embryo of the fifth day. (Quain.) 
 
 A, ventral root; B, dorsal root; C, motor nerve-cells; D, sympathetic 
 ganglion-cells; E, spinal ganglion-cells still bipolar; F, mixed nerve; b, c. d, 
 motor nerve-fibres passing to and ramifying in /, developing dorsal muscles; 
 e, a sensory nerve-trunk. 
 
 Fig. 17-B. Spinal ganglion-cells showing transition from bipolar to unipolar 
 
 condition. (Quain.) 
 
 28 
 
THE NERVOUS SYSTEM 
 
 spinal cord to terminate in the neighborhood of some central cell 
 developed from the original neural groove. The two processes of 
 the afferent cell at their origin from^the cell ultimately approach 
 
 Fig. 18. Diagram of the arrange- 
 ment of the sensory nerve-fibres 
 in the olfactory organ and bulb. 
 (Quain.) 
 
 n, nerve-fibre coming off from 
 sensory nerve cell; gl., synapse 
 within olfactory glomerulus; n, 
 nerve-cell and nerve of olfactory 
 bulb of brain. 
 
 Fig. 19. Diagram of the connec- 
 tions of the retinal elements. 
 (Quain.) 
 
 s, sensory nerve-cells ; gr. i, in- 
 ner granules; ra. i., inner molec- 
 ular layer; g., ganglion-cell; n, 
 its nerve-fibre process ramifying 
 in the nerve-centre. 
 
 each other so that they finally form a T and appear to be given off 
 from a common stem. Because of the double process originally 
 possessed by these cells they are called in the early period of their 
 development bipolar cells. (Figs. 17, A and B.) In mammals all 
 ultimately become unipolar except the cells of the spiral and ves- 
 tibular ganglia, from which the fibers of the eighth cranial nerve 
 grow. These retain the primitive bipolar arrangement. 
 
 30 
 
THE NERVOUS SYSTEM 
 
 The Development of the Medullary Sheath Some time after 
 the outgrowth 'of the axis cylinder the medullary sheath is formed, 
 apparently through the agency of the axon itself. The philogenet- 
 
 auditory 
 
 gustatory 
 
 tactile 
 
 Fig. 20. Diagram showing the mode of termination of sensory nerve-fibres 
 in the auditory, gustatory, and tactile structures of Vertebrata. (Quain.) 
 
 ically youngest fibers in the body acquire a medullary sheath later 
 than others. Representatives of this class are the fibers of the 
 pyramidal tracts and the long posterior columns of the spinal cord. 
 
THE NERVOUS SYSTEM 
 
 THE MORPHOLOGY OP NERVOUS TISSUE 
 
 The Structure of a Nerve Cell (Figs. 21-30) A nerve cell 
 possesses, like all cells, a nucleus. The nucleus, though of large 
 size, contains very little chromatin, generally collected as two small 
 nucleoli within the nucleus. Throughout the nerve cell run many 
 fibrillge which appear in well prepared specimens as delicate stria- 
 tions. These fibrillae are continued out of the cell into the processes 
 of the cells between the Nissl substance. The 
 Nissl substance is very abundant except at that 
 region from which the axis cylinder leaves the 
 cell. In this region many fibrillae are collected 
 together to enter the axis cylinder. It is called 
 the axon hillock of the cell. The cell processes 
 are of two kinds and have already been indi- 
 cated. 
 
 The Axis Cylinder and Dendrites The 
 axis cylinder is smaller than the other processes, 
 where it leaves the cell, but much longer, run- 
 Fig. 21. Two mo- ning, i n the case of motor cells of the spinal 
 tor nerve - cells . , . , ,-,-, 
 
 from the dog. cord > to tne periphery of the body. 
 (Quain.) The dendrites are usually thick where they 
 
 after a"eriod of leave the Cel1 ^ut SOOn break U P i nto manv 
 prolonged activ- processes which form a network with similar 
 
 ffom <P p?epSo^ P rocesses of other cells not far from the cell 
 by Dr. Gustav from which they originate. 
 
 Neurons A nerve cell with its processes is 
 
 termed a neuron. The function of neurons is to 
 
 transmit nervous impulses and, corresponding to the direction of 
 
 the impulse, there are two varieties of neurons the sensory or 
 
 afferent neurons, and the motor or efferent neurons. 
 
 An afferent neuron functionally connected through the central 
 nervous system with an efferent neuron constitutes a reflex arc. 
 Though an impulse may be transmitted in either direction along a 
 nerve fiber it can only traverse a reflex arc in one direction. This 
 phenomenon is termed the law of forward direction. 
 
 The Structure of Nerves (Figs. 31-32) All the nerves which 
 are given off from the central nervous system, the brain and spinal 
 cord, possess a medullary sheath. This consists of a fatty substance 
 termed myelin, imbedded between the meshes of a network. The 
 
 34 
 
THE NERVOUS SYSTEM 
 
 Fig. 22- A. Ramified nerve-cell 
 from ventral horn of spinal 
 
 cord of man. (Quain.) 
 a, axis-cylinder process; b, cell- 
 body with nucleus and clump of 
 pigment-granules; d, d, dendrons. 
 
 Fig. 22-B. Axis-cylinder process 
 
 of a nerve cell. (Quain.) 
 x, x, portion of nerve-cell from 
 spinal cord of ox, with axis-cylin- 
 der process, a, coming off from it 
 and acquiring at a 1 a medullary 
 sheath, highly magnified. 
 
 36 
 
THE NERVOUS SYSTEM 
 
 Fig. 23. Multipolar and unipolar types of nerve-cell. (Quain.) 
 
 A, large pyramidal cell of cerebral cortex, human, Nissl method. (Cajal.) 
 a, axon; b, cell-body; c, apical dendron; d, placed between two of the basal 
 dendrons, points to the nucleus of a neuroglia-cell. 
 
 B, unipolar cell from spinal ganglion of rabbit, Nissl method. (Cajal.) 
 a, axon; b, circumnuclear zone, poor in granules; c, capsule; d, network 
 within nucleus; e, nucleolus. 
 
 38 
 
THE NERVOUS SYSTEM 
 
 Fig. 24. Nerve-cells of kitten ' (from the anterior corpora quadrigemina) 
 
 showing neuro-fibrils. 
 a, axon; b, c, d, various parts of the intracellular plexus of fibrils. 
 
 40 
 
THE NERVOUS SYSTEM 
 
 W 
 
 Fig. 25. Nerve-cells of lizard: A and D during activity, B and C during 
 
 hibernation. (Quain.) 
 
 a (in J3), axon; b, b (in A and B), knob-like endings of extraneous fibrils; 
 c, d (in C), superficial and deep fibril networks. 
 
 42 
 
THE NERVOUS SYSTEM 
 
 Fig. 26. A long-axoned nerve-cell from the cerebral cortex. (Quain.) 
 a, axis-cylinder process with collaterals; d, d, dendrons; b, body of cell. 
 
 44 
 
THE NERVOUS SYSTEM 
 
 Fig. 27. A short-axoned cell from the cerebral cortex. Golgi method. (Quain.) 
 a, a', a", axon and its ramification; d, d, d, dendrons. 
 
 46 
 
THE NERVOUS SYSTEM 
 
 Fig. 28. Cell from cerebral cortex, showing varicosities on its dendrons and 
 
 not spines. Methylene-blue method. (Quain.) 
 
 a, axon; b, c, a branching collateral (both this and the main axon show a 
 medullary sheath) ; d, varicose dendrons. 
 
 48 
 
THE NERVOUS SYSTEM 
 
 Fig. 29. Synaptic ramifications of axon of one nerve-cell, B, around the 
 
 bodies of other cells, A. From the cerebellum of the rat. (Quain.) 
 
 a, b, c, ramifying axon; d, dendrons. 
 
 Fig. 30. Two motor cells from the rabbit's spinal cord, which show chromat- 
 olysis as the result of section (fifteen days previously) of the 
 
 nerve-fibres which arise from them. (Quain.) 
 
 In A the chromatolysis is rather less advanced than in B. In both the 
 nucleus has moved to the periphery, and the cell-substance (b and c) is 
 swollen, a, axon-process of A. 
 
 Fig. 31. Transverse and longitudinal section of medullated nerve-fibre of 
 
 frog (osmic acid and acid fuchsine). (Quain.) 
 
 The longitudinal section shows one node of Ranvier and two of Lanter- 
 mann's clefts. The fibrillar structure of the axis-cylinder is shown in both 
 longitudinal and transverse section. 
 
 50 
 
THE NERVOUS SYSTEM 
 
 sz ... 
 
 network is composed of a substance termed neurokeratin. Outside 
 
 the myelin substance is a sheath 
 termed the neurolemma. Inside the 
 myelin and separating it from the axis 
 cylinder is the axolemma. The axis 
 cylinder itself is composed of many 
 fine fibrillge, the so-called neurofibrillae. 
 At certain intervals along the nerve 
 fiber, intervals proportionate to the 
 diameter of the nerve fiber and vary- 
 ing from 80 to 600 microns, the mye- 
 lin substance suffers interruption so 
 that the medullary sheath dips down 
 to touch the axis cylinder. These in- 
 terruptions are called the nodes of 
 Ranvier. The nerve fibers of the 
 peripheral nerves run in bundles, sur- 
 rounded and held together by a con- 
 nective tissue sheath termed the peri- 
 neurium. 
 
 sz 
 
 Fig. 32. Scheme of structure of medullated 
 
 peripheral nerve fibre of a fish. 
 - i eo (Nemileff.) 
 
 A, Cross section; B, longitudinal section; 
 on left fibre is shown as stained intra vitam 
 with methylene blue; on right, myelin is 
 shown black as in osmic* acid staining with 
 the incisures of Schmidt indicated; sz, cells 
 of sheath of Schwann; n, their nuclei; ss, 
 sheath of Schwann; sp, processes of the 
 cells of sheath of Schwann or the myelin 
 sheath network; le, larger trabeculse of pro- 
 - sp toplasmic framework of medullary sheath 
 arranged obliquely to axis-cylinder and 
 Pf forming the so-called "funnels"; Ieo, clear 
 streaks in fibres treated with osmic acid, cor- 
 responding to le, incisures of Schmidt; mo, 
 myelin blackened with osmic acid; ax axis- 
 cylinder; pa, periaxial space around axis- 
 cylinder; gs, "coagulated fluid" in periaxial 
 space; pf, peripheral, non-fibrillar, part of 
 axis-cylinder; f, neurofibrils of axis-cylinder; 
 r, ring-like thickening of Schwann's sheath 
 at node of Ranvier; o, cavity in r. (Bailey.) 
 
 52 
 
THE NERVOUS SYSTEM 
 
 The Varieties of Peripheral Endings of Sensory Nerves The 
 
 peripheral process of the afferent nerve cell forms a connection 
 with the peripheral epithelium in a variety of ways. 
 
 Fig. 33. Nerve and nerve endings in the skin and hair follicles. (After 
 
 G. Retzius.) 
 
 As, Outer root sheath; c, most superficial nerve-fibre plexus in the cutis; 
 dr, sebaceous glands; h, the hair itself; hst, stratum corneum; is, inner root 
 sheath of hair; n, cutaneous nerve; rm, stratum germinativum Malpighii. 
 (Bailey.) 
 
 1. In some instances it merely terminates by ramifying between 
 epithelial cells. Losing its medullary sheath it divides a number 
 
 54 
 
THE NERVOUS SYSTEM 
 
 of times. Each division ending in a little knob between epithelial 
 cells. (Fig. 33.) Nerve fibers end in this manner which run : 
 
 (1) To the skin. 
 
 (2) To the mucous membranes. 
 
 (3) To connective tissue. 
 
 (4) To the glandular epithelium. 
 
 (5) 
 (6) 
 (7) 
 
 To certain serous surfaces. 
 
 To the outer sheath of the root of a hair follicle. 
 
 To the teeth. Whether the dentine is penetrated by nerve 
 fibers is a matter of dispute. 
 
 2. In certain regions of the body where special sensitiveness is 
 required these endings are formed by a 
 combination of complicated variations 
 of the sensory epithelium with the 
 nerve ending. The simplest of these 
 special end organs is the tactile cell. It 
 consists of an epithelial cell with a pro- 
 longed inner extremity which comes 
 into contact with a leaf-like expansion 
 of the end of the nerve fiber. 
 
 3. A more complex ending is the 
 compound tactile cell. This consists of 
 several epithelial cells grouped together 
 and in contact with one nerve ending. 
 Representatives of this class are the cor- 
 puscles of Grandry and Merkel's cor- 
 puscles. (Figs. 34 and 36.) 
 
 4. End bulb. In this form the bul- 
 bous end of the axons terminate in a 
 special granular matter inclosed in a 
 capsule of flattened connective tissue 
 like cells. They occur in the mouth and 
 conjunctiva. (Fig. 35.) 
 
 5. Compound end bulbs are combinations of several simple end 
 bulbs containing several nerve endings. They occur in the nose, 
 rectum, peritoneum tendon, ligaments, joints and in the trunks of 
 nerves upon the glans penis and clitoris. (Fig. 37.) 
 
 6. Pacinian bodies. In this form the axis cylinder terminates in 
 a rod which is inclosed in alternate concentric layers of a modified 
 
 56 
 
 Fig. 34. Tactile corpuscle 
 within a papilla of the 
 skin of the hand, stained 
 with chloride of gold. 
 (Quain.) 
 
 n, two nerve-fibres passing 
 to the corpuscle; a, a, vari- 
 cose ramifications of the 
 axis-cylinders within the 
 corpuscle. 
 
THE NERVOUS SYSTEM 
 a t t 
 
 Fig. 35. Herbst corpuscle of duck. (Quain.) x 380 diameters. 
 n, medullated nerve-fibres; a, its axis-cylinder, terminating in an enlarge- 
 ment at end of core; c, nuclei of cells of core; t, nuclei of cells of outer 
 tunics; t', inner tunics. 
 
 Fig. 36. Corpuscles of Grandry from the duck's tongue. (Quain.) 
 A, composed of three cells, with two interposed discs, into which the axis- 
 cylinder of the nerve, n, is observed to pass; in B there is but one tactile 
 disc enclosed between two tactile cells. 
 
 Fig. 37. A medullated fibre terminating in several end-bulbs in the human 
 peritoneum. Lower power. Methylene-blue preparation. (Quain.) 
 
 58 
 
THE NERVOUS SYSTEM 
 
 Fig. 38. Magnified view of a Pacinian body from the cat's mesentery. 
 
 (Quain.) 
 
 n, stalk of corpuscle with nerve-fibres, enclosed in sheath of Henle, passing 
 to the corpuscle n', its continuation through the core, m, as axis-cylinder only; 
 o, its terminal arborization; c, d, sections of epithelioid cells of tunics, often 
 mistaken for the tunics themselves; /, channel through the tunics which ex- 
 pands into the core of the corpuscle. 
 
 60 
 
THE NERVOUS SYSTEM 
 
 Fig. 39. Nerve-endings upon the intrafusal muscle-fibres of a muscle-spindle 
 
 of the rabbit. Moderately magnified. Methylene-blue 
 
 preparation. (Quain.) 
 
 a, large medullated fibre coming off from "spindle" nerve and passing to 
 end in an annulo-spiral termination on and between the intrafusal fibres; 
 b, fine medullated fibres coming off from the same stem and dividing. Its 
 branches, c, pass towards the ends of the muscle-fibres and terminate in a 
 number of small localized arborizations, like end-plates. 
 
 Fig. 40. Sensory nerve terminating in arborizations around the ends of 
 muscle-fibres. (Quain.) 
 
 Fig. 41 .--An annulo-spiral ending of intrafusal fibre. Highly magnified. 
 Methylene-blue preparation. (Quain.) 
 
 62 
 
THE NERVOUS SYSTEM 
 
 Fig. 42. Organ of Golgi from the human tendo achillis. Chloride of gold 
 
 preparation. (Quain.) 
 
 m, muscular fibres; t, tendon-bundles; G, Golgi's organ; n, two nerve- 
 fibres passing to it. 
 
 Fig. 43. Ending of nerve-fibres in cardiac muscle. (Quain.) 
 
 Fig. 44. Motor nerve-ending in the abdominal muscles of a rat. Gold 
 preparation. Magnified 170 diameters. (Quain.) 
 
 64 
 
THE NERVOUS SYSTEM 
 
 Fig. 45. Terminal nerve-fibrils in an alveolus of the submaxillary gland 
 
 of the dog. Chromate of silver method. ^ (Quain.) 
 The extension of the lumen into the crescents of Gianuzzi is also shown. 
 
 Fig. 46. Motor end-organ of a lizard. Gold preparation. (Quain.) 
 n, nerve-fibre dividing as it approaches the end-organ; r, ramification of 
 axis-cylinder upon, b, granular bed or sole of the end-organ; m, clear sub- 
 stance surrounding the ramifications of the axis-cylinder. 
 
 66 
 
THE NERVOUS SYSTEM 
 
 Fig. 47. Nerve-ending in muscular fibre of lizard (lacerta viridis). (Quain.) 
 A, end-plate seen edgeways; B, from the surface; s, s, sarcolemma; pp, ex- 
 pansion of axis-cylinder. In B the expansion of the axis-cylinder appears 
 as a clear network branching from the divisions of the medullated fibres. 
 
 Fig. 48. Ending of motor nerves in rabbit's muscle. Reduced silver method. 
 
 (Quain.) 
 
 a, axis-cylinder of entering nerve; b, c, parts of terminal ramification 
 showing network of neuro-fibrils. 
 
 68 
 
THE NERVOUS SYSTEM 
 
 , epithelium containing fluid between them. These occur in the 
 palms of the hands, the soles of the feet, in the parietal peritoneum, 
 the mesentery, mammary gland, tendons, ligaments, joints, and 
 penis, clitoris and in the voluntary muscles. (Fig. 38.) 
 
 7. Besides the Pacinian bodies sensory nerves to muscular fibers 
 terminate in expansions which form (a) annular, (&) spiral and 
 (c) arborizing expansions around the muscular fibers. (Figs. 
 39-41.) 
 
 8. Special arborizations upon the tendons are termed organs of 
 Golgi. (Fig. 42.) 
 
 9. All motor nerves terminate at the muscular fibers by branch- 
 ing in a mass of granular substance superficial to the muscular fiber 
 but beneath the sarcolemma. This ending is termed the motor end 
 plate. All these modifications of endings have developed for the 
 purpose of delicately transmitting slight molecular changes of a 
 refined order to or from a sensitive cell. (Figs. 43-48.) 
 
 The more complex the connection between the termination of the 
 nerve and the sensitive surface, the more refined and delicate and 
 special is the sensation or motor impulse transmitted. In other 
 words, in those regions in which sensations of a special sensitive- 
 ness or of a special kind must be transmitted there is need of a 
 special device, which exists in the form of these complex nerve 
 endings. 
 
 The importance of even simple nerve endings is made clear by 
 the disorderly character of a reflex excited by stimulating the cut 
 nerve endings after dissecting off the skin. 
 
 70 
 
THE NERVOUS SYSTEM 
 
 PHYSIOLOGY OF NERVES 
 
 The Classification of Nerves Nerves may be classified as fol- 
 lows i- 
 
 Efferent. . 
 
 ' Excitatory 
 
 Motor 
 
 Secretory - 
 
 Motor 
 
 Vasomotor 
 
 Cardiomotor 
 
 Visceromotor 
 
 Pilomotor 
 
 Salivary 
 Gastric 
 Pancreatic 
 Sweat 
 
 Inhibitory 
 
 Trophic 
 
 Afferent . 
 
 Excitatory 
 
 f Motor for all sub. div. of motor nerves 
 
 [ Secretory for all sub. div. of secretory nerves 
 
 Visual 
 
 Auditory 
 
 Equilibrial 
 
 Olfactory 
 
 Gustatory 
 
 Pressure 
 
 Temperature 
 
 Pain 
 
 Hunger 
 
 Thirst 
 
 r Sensory 
 
 Reflex 
 
 Reflex for various efferent nerves 
 
 Inhibitory 
 
 Trophic 
 
 Inhibitory upon conscious sensations have not 
 been demonstrated 
 
 The reflex fibers which cause unconscious re- 
 flexes are known to be inhibited in some 
 cases at least 
 
 72 
 
THE NERVOUS SYSTEM 
 
 The Velocity of an Impulse along a Motor Nerve is measured by 
 stimulation of the nerve of a muscular nerve preparation at two 
 points, separated by a known distance, and recording upon a mov- 
 ing surface the time of application of each stimulus and the time 
 of response (contraction of the muscle) to each stimulus. 
 
 The difference between the time of application of the stimulus 
 and the response in the two cases will be the time it has taken the 
 impulse to travel the known distance which separates the electrodes. 
 The velocity in a frog's nerve is 28 meters a second, and in warm 
 blooded animals is 60 to 120 meters a second. (Fig. 49.) 
 
 Fig. 49. Apparatus arranged for determining speed of motor nerve impulse. 
 By means of turn-over key (1), the current from the cell (2), through the 
 inductorium (3) may be applied to the nerve at the two points (4 and 5). 
 The difference in time in the contraction of the muscle is indicated by the 
 difference in the rise of the lever (6) on the cylinder (7) in fractions marked 
 at (8). 
 
 The Velocity of an Impulse along a Sensory Nerve can only be 
 measured by measuring, in the same manner, the velocity of the 
 electrical change which accompanies the propagation of the im- 
 pulse. It is about the same as the velocity of propagation along a 
 motor nerve. 
 
 The velocity of propagation varies with the species of animal. 
 In general it is proportional to the height in the scale of life of the 
 animal in question. 
 
 The Direction of the Impulses The direction of propagation 
 along a nerve fiber may be ascertained by noting the direction of 
 spread of the electrical current accompanying the propagation of 
 the impulse. The impulse is found to travel in both directions from 
 the point stimulated. 
 
 74 
 
THE NERVOUS SYSTEM 
 
 A Demonstration that Nerve Impulses Travel in both Direc- 
 tions The gracilis muscle of a frog is separated longitudinally 
 into halves hy a tendinous intersection. The axis cylinders supply- 
 ing these two divisions are divisions of the axis cylinders them- 
 selves, which run to the muscle. Stimulation of the distal portion 
 of the divisions of the axis cylinders supplying one half will cause 
 a contraction of the whole muscle, whereas stimulation of the muscle 
 alone, i.e., in a place free from nerve fibers, will cause a contraction 
 in only one half of the muscle. In the first instance the impulse 
 must have traveled up the set of axis cylinders of the stimulated 
 half and down the branches into the unstimulated half, thus travel- 
 ing in both the direction of the course of the nerve in one part and 
 in the opposite direction to the course of the nerve in the other part. 
 
 Bell and Majendie 's Law Though an impulse may travel in 
 either directibn of a nerve, the same nerve cannot be both afferent 
 and efferent. This fact has been enunciated into a law by Bell and 
 Majendie and is known as their law. The difference in the function 
 of nerves expressed by the law of Bell and Majendie is not depen- 
 dent upon any essential difference in the nerve but solely upon 
 their central and peripheral connections, a fact which may be dem- 
 onstrated by grafting experiments. 
 
 Events Accompanying the Passage of a Nerve Impulse The 
 Expenditure of Energy The fact that a nerve loses its irritability 
 in the absence of oxygen indicates that the process of excitation is 
 accompanied by the consumption of oxygen and, therefore, the 
 dissipation of energy. The consumption of energy, however, must 
 be extremely small inasmuch as the most sensitive methods for 
 measuring heat have failed to detect any rise of temperature accom- 
 panying the passage of a nervous impulse. 
 
 The Demarcation Current If the terminals of a delicate gal- 
 vanometer are connected to a resting uninjured nerve no current 
 through the nerve will be detected. If, however, the nerve is di- 
 vided and one of the poles of the galvanometer circuit is connected 
 with the injured end, while the other pole is in contact with the side 
 of the nerve at some distant point, the needle of the galvanometer 
 will swing, indicating in the first place the existence of a current 
 in the nerve and in the second place that the current passes through 
 the nerve from the end pole to the lateral pole. In terms of the 
 outside circuit the pole on the end of the nerve is negative to all 
 
 76 
 
THE NERVOUS SYSTEM 
 
 other points. This current is called a demarcation current and is 
 excited by the injury to the nerve incidental to its division. 
 
 Current of Action If now an impulse is excited in the nerve 
 by stimulating it above the site of application of the poles of the 
 galvanometer the needle of the galvanometer will swing in an oppo- 
 site direction, indicating a current in the opposite direction. This 
 current is the current of action or the current accompanying the 
 passage of an impulse which passes from the stimulated point in 
 both directions and consequently toward the injured end. It has 
 been called the negative phase of the demarcation current. The 
 demarcation current is strongest immediately after division of the 
 nerve and quickly subsides as the nerve dies up to the node of 
 Ranvier nearest to the cut end. It may again be excited by a fresh 
 division above this node. The current of action travels with the 
 same rate as the nervous impulse 28-33 meters a second. It is 
 18 m. in length and lasts only 6/10,000-8/10,000 of a second at any 
 one point. 
 
 Conditions Affecting the Passage of a Nervous Impulse 
 Temperature Conduction along a nerve is much diminished by 
 decreasing the temperature. A temperature between and 5 C. 
 is sufficient to check conductivity in a mammalian nerve. The 
 temperature coefficient for each difference in temperature of 10 C. 
 is 1.79. This amount is a constant factor by which the velocity 
 of conduction along a nerve fiber may be multiplied to give the 
 velocity at 10 C. higher temperature. 
 
 Fatigue Nerve fibers cannot be fatigued, at least by excessive 
 excitation, but a nerve muscular preparation quickly shows signs 
 of fatigue from repeated excitation. 
 
 Demonstration of the Site of Fatigue in the Nerve Muscle 
 Mechanism After the preparation has been fatigued the muscle 
 may be excited to contraction by direct stimulation, showing that 
 the muscle, at least, is not the most quickly fatigued of the various 
 components of a muscle nerve preparation. In considering the seat 
 of fatigue of a nerve muscular preparation, besides the muscle, 
 the motor end plate and the nerve are to be considered. Two 
 agents will enable us to eliminate the nerve as the seat of fatigue. 
 One is curare and the second is the passage of the constant cur- 
 rent. Curare specifically paralyzes the motor end plate. If it is 
 applied to a muscular nerve preparation the nerve may be con- 
 
 78 
 
THE NERVOUS SYSTEM 
 
 tinuously stimulated without affecting the motor end plate or the 
 muscle, because of the block produced at the motor end plate by 
 curare. After the effect of the curare wears off or after it is set 
 aside by its antagonist physostigmin, the 
 muscle again may be stimulated by stimula- 
 tion of the nerve, showing that, although the 
 nerve had been excited for a much longer 
 time than would have been necessary to 
 fatigue both the motor end plate and the 
 muscle during the time that both were pro- 
 tected by the curare, the nerve is still capable 
 of transmitting an impulse. 
 
 A constant current possesses the power of 
 blocking impulses through a nerve. It may be 
 used in the same manner as curare to protect 
 the motor end plate and muscle from excita- 
 tion during a period of prolonged stimulation 
 of the nerve of a nerve muscle preparation 
 above the point of application of the constant 
 current. (Fig. 50.) 
 
 Drugs The action of drugs upon nerves 
 may be tested by inclosing the nerve of a 
 muscle nerve preparation within a closed 
 tube. The nerve issues through the ends of 
 the tube, which are closed with normal saline 
 clay. Into the tube may then be conducted 
 the vapor of the drug, the action of which it 
 is desired to test. The effect of these drugs 
 may then be tested upon both the excitability 
 of the nerve and its conductivity. 
 
 Excitability may be tested by means of 
 electrodes which make connections with the 
 portion of the nerve inclosed within the tube. 
 Conductivity may be tested by electrodes 
 making contact with a portion of the nerve 
 outside of that end of the tube which is opposite to the end nearest 
 the muscle end of the nerve muscle preparation. 
 
 Fig. 50. Indefatig- 
 ableness of the 
 
 nerves. 
 
 Two muscles, Mi, 
 Mz, furnished with 
 their nerves, Ni, Na, 
 are simultaneously 
 stimulated at x by an 
 induced current. The 
 nerve, Nz, is anelec- 
 trotonized at B by a 
 constant current, Z, 
 so as to prevent the 
 impulse reaching the 
 muscle, M 2 , thus to 
 prevent this muscle 
 being fatigued. The 
 muscle, Mi, is quick- 
 ly fatigued and ceases 
 to contract. If then 
 the cell current is 
 broken, while the 
 stimulation of the 
 two nerves continues 
 at x, the muscle, M 2 , 
 will be seen to con- 
 tract ; therefore its 
 nerve has not felt the 
 effects of fatigue. 
 
 80 
 
THE NERVOUS SYSTEM 
 
 Fig. 51. Apparatus for exposing a portion of a nerve to gases and for testing 
 the excitability and conductivity of the exposed portion 
 
 1 Exposed portion of nerve. 
 
 2. Tube containing the gas with inlet and outlet. 
 
 3. Electrodes for testing excitability. 
 
 4. Electrodes for testing conductivity. 
 
 Effect of Carbon Dioxide and Ether, Chloroform and Alcohol 
 Carbon dioxide and ether diminish first excitability, and then con- 
 ductivity. Chloroform rapidly diminishes excitability and conduc- 
 tivity and far more intensely than ether, so that recovery may not 
 be complete. Alcohol diminishes conductivity without at first 
 affecting excitability. (Figs. 51, 52.) 
 
 Fig. 52. Illustrates the effect of ether vapor upon excitability and con- 
 ductivity. Following the exposure of the nerve to ether there is a disap- 
 pearance of excitability. The dotted vertical lines illustrate a response to 
 the application of the current to the portion of the nerve surrounded with 
 ether vapor. The straight vertical lines indicate a response of the nerve 
 to the stimulation applied to a point outside the portion exposed to the 
 ether vapor. The stimulus is therefore alternately applied to the nerve 
 inside and outside of the tube. 
 
 At 1 there is a disappearance of excitability. 
 
 At 2 there is a reappearance of excitability. 
 
 At 3 there is a disappearance of excitability. 
 
 At 4 there is a disappearance of both excitability and conductivity. 
 
 At 5 there is a reappearance of conductivity and 
 
 At 6 a reappearance of excitability. 
 
 82 
 
THE NERVOUS SYSTEM 
 
 EVENTS ACCOMPANYING THE ELECTRICAL EXCITATION OP NERVES 
 
 The Minimal Effective Stimulus is ascertained by exciting a 
 nerve muscular preparation from the discharge of a condenser 
 charged with decreasing potential until the minimal stimulus is 
 found. (Fig. 53.) For frogs' nerve it is 1/1000 of an erg (an erg 
 being the amount of energy produced or work performed by the 
 action of one dyne through one centimeter. A dyne gives an ac- 
 celeration of one centimeter per second to one gram). 
 
 Summations If several subminimal stimuli are applied suf- 
 ficiently close together so that each successive stimulus affects 
 
 Fig. 53. Illustrating the apparatus for exciting the nerve from a condenser 
 
 with a definite quantity of electricity. 
 
 1. Switch for throwing, first, the rheostat, 2, and, second, the condenser, 3, 
 into the circuit of the electrodes upon the nerve. 
 
 the nerve before the effect from the first one has passed off the 
 combined effect may produce excitation though each individual 
 stimulus would fail to do so. This phenomenon is called sum- 
 mation. 
 
 The Refractory Period For a brief time after the application 
 of an electrical current to a nerve it remains unexcited. This 
 period is called the refractory period and amounts to .002-. 0006 
 of a second according to the temperature. The existence of a 
 refractory period is common to all forms of excitable tissue, and 
 is best illustrated in heart muscle. After the application of a 
 stimulus to heart muscle, the change producing contraction may 
 be said to be progressing, and it is during this period that the 
 muscle is refractory to another stimulus of the same strength, for 
 the simple reason that it is already responding to the first stimu- 
 
 84 
 
THE NERVOUS SYSTEM 
 
 lus. If, however, a very strong stimulus is applied within the re- 
 fractory period it may respond, so that the refractory period de- 
 pends on the strength of the stimulus used. However, after such a 
 response it remains irresponsive to normal stimuli for a longer 
 time, thus indicating the causes upon which the refractory period 
 depends, namely a breaking down of material available for re- 
 sponse, the response depending upon the katabolic changes. 
 
 Site of the Excitation When the constant current is made 
 use of to excite a nerve, an excitation occurs at the make, and, 
 
 Fig. 54. Apparatus for determining the site of excitation of the muscle, 
 whether at the anode or the cathode, at either the make or the break. 
 B, Battery; K, key, by means of which the current is made or broken; 
 
 C, clamp holding the muscle by its middle movable electrodes, EE, capable 
 
 of recording the movements upon the paper, P. 
 
 assuming that the current is strong enough, at the break also; a 
 make excitation starts at the cathode and a break excitation starts 
 at the anode. Inasmuch as what is true for one excitable tissue is 
 true, in this respect, for another, muscle may be used to demon- 
 strate the fact. 
 
 ^(a) It may be clamped lightly in its middle and the two 
 electrodes attached to the two ends, each electrode being capable 
 of a swing in towards the muscle. At the make contraction the 
 cathode electrode will swing in towards the muscle; at the break 
 contraction the anode will do the same. (Fig. 54.) 
 
 (b) Inasmuch as injury or death of the end of a muscle will 
 prevent its irritability, a muscle injured at one end may be used 
 to demonstrate the starting point of the contraction at the make 
 
 86 
 
THE NERVOUS SYSTEM 
 
 and break. At the make no contraction will occur if the cathode 
 is attached to the injured end, and vice versa. 
 
 Electrotonus It has been said that contraction only occurs 
 at the make and break of a constant current. If the current is 
 strong enough the excitability of the nerve of a muscular nerve 
 preparation may be so increased that the muscle may be thrown 
 into a state of continued contractions, called closing tetanus, all 
 the time during which the current is passing. 
 
 Polarising 
 Current 
 
 Excitab. diminished 
 
 Fig. 55. Determination of excitability of the myopolar segment during the 
 
 passage of a current through a certain length of the nerve. 
 In the lower figure the polarizing current is ascending; excitability is di- 
 minished in the myopolar segment. In the upper figure the polarizing current 
 is descending; the excitability of the myopolar segment is increased. 
 
 An "after tetanus" may also follow the break of a strong 
 ascending current which has been passing for a considerable time. 
 With moderate or usual currents, however, no apparent change 
 occurs during the time the constant current passes. 
 
 Electrotonus and Method of Its Detection A change never- 
 theless does occur during this period between the make and break 
 of a constant current which is capable of detection by stimulating 
 different portions of the nerve by an induced current acting as an 
 analyzer. During the time that the constant current is passing, 
 the analyzer will detect a region near the cathode of the constant 
 current where the excitability is increased, and hence a greater 
 stimulus or impulse may be produced by a submaximal stimulus 
 than would result in the absence of the constant current. In the 
 same manner a region near the anode can be demonstrated in 
 which the irritability is diminished. (Fig. 55.) 
 
 88 
 
THE NERVOUS SYSTEM 
 
 Catelectrotonus and Anelectrotonus The increased irrita- 
 bility at the cathode is called catelectrotonus and the diminished 
 excitability at the anode is called anelectrotonus. Inasmuch a 
 the impulse leading to contraction at the make begins at the cathode 
 it may be said that the excitability is due to a rise of irritability 
 at the cathode, dependent upon the sudden development of cak 
 electrotonus. In the same manner the rise of excitability at the 
 anode accompanying the break is due to sudden passing off oi 
 anelectrotonus. The above is true for currents of moderate 
 strength. When stronger currents are used the indifferent point 
 separating the two regions of anelectrotonus and catelectrotonus 
 from each other comes to lie nearer the cathode, so that more ana 
 more of the nerve is in a condition of anelectrotonus. 
 
 Pfliiger's Law In the case, therefore, of very strong cur- 
 rents the whole interelectrodal portion of the nerve is in a con- 
 dition of anelectrotonus and the depression of irritability at the 
 anode at the make is so great that the nerve is non-conductive at 
 this point. Consequently when strong currents are used to pro- 
 duce stimulation, and the current is an ascending one, no im- 
 pulse can reach the muscle at the make because the make excitation 
 starts at the cathode, which is furthest from the muscle. In 
 ascending currents it is blocked by the high degree of anelec- 
 trotonus at the anode. In the same manner at the break of descend- 
 ing currents, when strong currents are used the excitation started 
 at the anode by the passing off of anelectrotonus cannot descend 
 past the cathode where there is a swing back from high catelec- 
 trotonus to a very low degree of irritability. These variations in 
 the results of stimulating nerves with varying degrees of current 
 have been formulated into a law called Pfluger's law, namely, 
 that the result of stimulating a nerve varies with the strength of 
 the current and is as follows : 
 
 ASCENDING DESCENDING 
 
 make break make break 
 
 weak c c 
 
 medium c c C c 
 
 strong C or T C or T 
 
 anelectrotonus block 
 
 (C strong contraction. c contraction. T tetanus. no 
 effect.) 
 
 90 
 
THE NERVOUS SYSTEM 
 
 For these reasons, when dealing with induced shocks we are 
 only dealing with make stimuli. The contraction at the break of 
 the primary circuit, which is evoked by the make of the make and 
 break produced in the secondary circuit, is stronger than the 
 contraction produced at the make of the primary, because the rise 
 of current at the make in the primary is a much slower change 
 than the fall of current at the break. In other words the intensity 
 of the currents induced in the secondary coils is proportional to 
 the r.ate of change of the current in the primary coil. 
 
 Application to the Human Being These results cannot be 
 ai plied to human nerves with the same exactness, because of the 
 
 Fig. 56. Diagram showing the internal polarization of the tissues. 
 All along the lines of the flow of the current, going from one pole to the 
 other, secondary polarities are developed across the heterogeneous portions, 
 traversed by electrolytic conduction. 
 
 impossibility of the direct application of the electrodes to the 
 human nerves. It is usual to apply one electrode (a stimulating 
 effect being most readily obtained when the stimulating electrode 
 is the cathode) over some point at which the various motor nerves 
 lie nearest to the surface. The other electrode, the indifferent one, 
 is applied over some other region of the body. Inasmuch as the 
 current, as it nears the cathode, becomes concentrated from a 
 more diffuse condition at a distance from this electrode called 
 the peripolar region, the current is strongest nearest to the elec- 
 trode as it passes across the nerves. It exists as opposite signs on 
 the two sides of the nerve and is stronger on the side nearest the 
 cathode. (Fig. 56.) Pure cathode and anode effects are not ob- 
 tainable. Applying the current in the manner described to the 
 human being gives the following phenomena in the order of the 
 strength of contraction produced : 
 
 92 
 
THE NERVOUS SYSTEM, 
 
 C C C (cathode closing, i.e. make contraction) 
 
 A C C (anode closing contraction) 
 
 A C (anode opening, i.e. the break contraction) 
 
 COG (cathode opening contraction) 
 
 Polarization and Its Explanation in the Extrapolar Region of 
 the Nerve The length of a nerve between the electrodes of a 
 current applied to the nerve is called the intrapolar or intraelec- 
 trodal portion. By sensitive galvanometers it may be shown that 
 a current passes also through the extrapolar region of the nerve 
 during the passage of a constant current. This current is in the 
 direction of the constant current which is applied to the nerve. It 
 
 Nerve. 
 
 Anelectrotonic 
 current. 
 
 Catelectrotonic 
 current. 
 
 Fig. 56a. Polarization of the nerve in its two extrapolar segments and 
 
 production of electrotonic currents in these two segments. 
 The middle region is traversed by a constant current (polarizing current;). 
 The extrapolar regions show currents of polarization of the same direction 
 as the preceding, but unequal in intensity. The anelectrotonic current is 
 more intense than the Catelectrotonic current. 
 
 is a different current from the current of action. The same extra- 
 polar current may be excited by the application of a constant cur T 
 rent to an artificial model of a nerve, consisting of a platinum wire 
 contained within a tube and surrounded within the tube by normal 
 saline solution or any other electrolyte. It will not occur, how- 
 ever, if the model is made of a zinc wire immersed in a satu- 
 rated solution of zinc sulphate. The phenomenon of these 
 extrapolar currents is purely physical and depends upon 
 polarization produced in the extrapolar regions of the nerve. The 
 .jjerve sheath may be regarded as composed in part of a solution 
 Electrolytes. (Fig. 56c.) 
 
 Upon the sheath in the neighborhood of the positive pole of 
 the polarizing current negative ions collect and in the same manner 
 
 94 
 
THE NERVOUS SYSTEM 
 
 positive ions collect in the neighborhood of the negative pole. In 
 fact it is only due to the fact that these two sets of ions are at- 
 tracted to the poles and give up their charges to them that any 
 current from the cell passes through the nerve at all. These 
 attracted ions at the points of application of the electrodes create 
 in this region a difference of potential which extends to the extra- 
 polar region. 
 
 The Current of Positive Polarization and Its Negative Varia- 
 tion In consequence of this fact a current will pass in the extra- 
 polar region. This current is called the current of polarization. 
 (Fig. 56a.) If now the electrodes of the constant current are taken 
 
 Fig. 56b. Post-electrotonic intrapolar currents produced after the cessation of 
 
 the polarizing current. 
 
 I, polarizing current; II, ordinary post-current of contrary direction or the 
 current of negative polarization; III, post-current whose direction is the 
 same as that of the polarizing current or the current of positive polarization. 
 
 away from the nerve and in their place the poles of a galvanometer 
 are applied, the galvanometer will show a temporary current in the 
 opposite direction to that in which the constant current was pre- 
 viously flowing, though immediately preceding this current in the 
 opposite direction there will be momentary current in the same 
 direction. This momentary current in the same direction is 
 known as the current of positive polarization, and that in the 
 opposite direction as the current of the negative variation of the 
 polarizing current. The current of positive polarization is really 
 the current of action excited by the break produced when the 
 electrodes are lifted off. The negative variation of the polarizing 
 current is due to the difference of potential created at the places 
 where the poles of the constant or polarizing current had collected 
 ions of unlike sign to that of the poles of the polarizing current 
 in the region of the poles. Inasmuch as the ions thus collected 
 at these spots are of unlike sign to that of the poles, the current 
 will flow in the opposite direction to that of the polarizing cur- 
 
 96 
 
THE NERVOUS SYSTEM 
 
 rent. (Figs. 56b and 56c.) These currents of polarization are 
 called electrotonic currents. 
 
 The electrotonic current excited in one of the two main branches 
 
 -i- - 
 
 Fig. 56c. Diagram illustrating the position of the ions which are responsible 
 for the direction of the current of negative polarization 
 
 indicated by the galvanometer, G. 
 
 When the current ceases to flow through the battery circuit, B, the col- 
 lection of a larger number of positive ions in the neighborhood of the pole, C, 
 causes the current to flow in the reverse direction through the galvanometer. 
 The plus and minus signs, D and E, indicate the direction of extra polar 
 electrotonic currents. 
 
 of a sciatic nerve is strong enough to excite an effective impulse 
 in the other branch. This effect is not due to spreading of the 
 current, as it will not occur if the stimulated branch is crushed. 
 
 THE PERIPHERAL NERVES 
 
 CONDITIONS AFFECTING ELECTRICAL STIMULATION OF THE NERVES 
 
 The Speed of the Make or Break An apparatus has been 
 devised which depends upon the rapid or slow opening of a shutter 
 controlling the size of an opening between two concentrated solu- 
 
 98 
 
THE NERVOUS SYSTEM 
 
 tions of zinc sulphate in which is immersed electrodes of zinc and 
 which is capable of more rapidly or slowly increasing the current. 
 -(Fig. 57.) 
 
 i 
 
 Fig. 57. A, Diagram of Rheonome. By means of the shutter, 1, the speed 
 of the make and break of the current between the electrolytes in the two 
 boxes, 2 and 3, communicating only through the slit, 4, may be varied. 
 
 B, Illustrating the galvanometer records of the change of the current obtained 
 by the differences of the speed of the make accomplished by the Rheonome. 
 
 The excitatory effect varies in proportion to the: 
 
 (1) Intensity of the current. 
 
 (2) And with certain limitations upon the rate of change 
 of the current. Rapid alterations in the current, as in very rapid 
 alterations of the induced current, are ineffective. It is for this 
 reason that the high voltage of the Tesla current may be used for 
 therapeutic effects upon the human being. 
 
 100 
 
THE NERVOUS SYSTEM 
 
 Waller's Characteristic The optimum rate of change is 
 known as Waller's characteristic. The rate of change may be 
 recorded graphically and is called the current gratient. 
 
 The Duration of a Current which is used to produce excitation 
 also bears important relations to the strength of excitation. This 
 relation may be investigated by first ascertaining the minimal 
 strength of current necessary to produce excitation and then deter- 
 mining how much the current must be increased as the time be- 
 tween the make and break is shortened to produce the same con- 
 traction. 
 
 Keith Lucas' Characteristic Keith Lucas has used as a second 
 characteristic that duration of the stimulus which will just pro- 
 duce an excitation when the strength of a minimal effective stimulus 
 is just doubled. Each tissue, muscle, nerve and nerve ending as 
 well as these various tissues in different animals have all their 
 definite various characteristics. 
 
 The Effect of Temperature upon Excitability Within certain 
 limits the excitability of a nerve may be increased by cooling. 
 Thus a frog's nerve cooled to 2 C. for a day will be so excitable 
 that simple section of the nerve may be sufficient to throw it into 
 a tetanus. This, however, is only true for mechanical stimuli. In 
 the case of electrical stimuli warming of the nerve increases irri- 
 tability and cooling diminishes it for all galvanic or induction 
 shocks of less duration than .005 of a second. In the case of 
 skeletal muscles excitability is increased by cooling for all forms 
 of stimuli. 
 
 The reason why the time of .005 of a second is a factor in the 
 effect of temperature on irritability is because the temperature 
 produces two effects which do not vary at the same rate with 
 changes of temperature. Thus cooling of a nerve both delays the 
 subsidence of the excitatory process and renders more difficult the 
 initiation of the excitatory change, but the delay in the subsidence 
 of the excitatory process reduces the amount of current needed 
 for excitation in an increasing ratio the longer the duration of the 
 current, while increasing the difficulty of the initiation of the exci- 
 tatory process such as is produced by (1) cooling, (2) prolonging 
 the current, (3) delaying its subsidence, increases also the current 
 required for excitation in the same ratio, or in an exponential 
 ratio as the current is lengthened. 
 
 102 
 
THE NERVOUS SYSTEM 
 
 Effect of Injury on Irritability Immediately after injury a 
 nerve is more irritable near the site of injury. After a time irri- 
 tability diminishes progressively in a downward direction, so that 
 the portion nearest the muscle is longest irritable. 
 
 Direction of Conductivity Across the Motor End Plate The 
 motor end plate, or the interval between the nerve and the muscle, 
 constitutes a true synapse. Conduction across it is only possible 
 in one direction. This is proved by the purely local contraction 
 which is excited by snipping a nerve-free portion of a split muscle 
 and contrasting the local contraction so excited with the contrac- 
 tions in both split portions when the ends of the nerves in one half 
 are snipped. 
 
 The Specific Delay at the End Plate A certain definite period 
 of delay exists in the transmission of an impulse across a motor 
 end plate. It has been found to be -.0013 of a second. The motor 
 end plate also shows fatigue more quickly than either the nerve 
 or muscle, a fact also indicated by the specific action of curare and 
 nicotine upon the motor end plate. 
 
 Action of Nicotine Nicotine, after a primary stimulant 
 action, has very much the same blocking effect upon the motor 
 end plate that curare possesses, though it is much less powerful 
 than curare. Four mg. of nicotine injected into the veins of a 
 anesthetized fowl, will cause a tonic contraction of all the muscles, 
 a phenomenon which may be immediately set aside by curare and 
 one which can occur when enough nicotine has been given to 
 paralyze all the motor nerves, or after all the motor nerves have 
 degenerated in consequence of their having been previously sec- 
 tioned. Thus nicotine, like curare, produces its effect by acting 
 upon the substance of the motor end plates. 
 
 Specific Optimal Excitation Time of the Motor End Plate 
 A fourth fact demonstrating the different essence of the motor 
 end plate is its different optimal excitation time. This represents 
 the relation of the strength of the current to the duration of the 
 current necessary to produce contraction. The muscle and the 
 nerve and motor end plate all possess different optimal excita- 
 tion times. The nerve-free end of the sartorious possesses an 
 excitation time of .017 seconds, and this may be taken as the excita- 
 tion time of the muscle. % 
 
 The excitation time of the sciatic nerve trunk is about .003 
 
 104 
 
THE NERVOUS SYSTEM 
 
 second, and possesses a steeper gradient. That then Is the excita- 
 tion time of nerve fibers. In the middle of the sartorious muscle 
 of the frog, in the region of the motor end plate, the excitation time 
 is .00005. 
 
 The Neuromuscular Juncture of the Sympathetic Nerves and 
 the Action of Adrenalin upon It The sympathetic nerve fibers 
 end seemingly in direct contact with the muscular fibers, without 
 the intermediation of any motor end organ. Nevertheless there 
 is evidence that here also there is present a third substance dif- 
 ferent from the nerve and muscle which bridges the gap between 
 the two though it has not organization, at least of a motor end plate. 
 Adrenalin possesses a specific stimulant action on the whole of that 
 portion of the sympathetic nervous system which causes augmenta- 
 tion of function. Hence it contracts all blood vessels supplied by 
 these nerves. Smooth muscle not innervated by the sympathetic 
 nervous system as that of the blood vessels of the brain and lungs is 
 unaffected by the injection of adrenalin. Therefore the action of 
 adrenalin cannot be upon the muscular fiber itself. Adrenalin is 
 just as effective, however, after complete degeneration of the post- 
 ganglionic fibers of the sympathetic nerves, so that its action cannot 
 be upon these post-ganglionic fibers themselves, but must be upon 
 some third substance intervening between this fiber and the muscle. 
 The same substance may be intermediary in all synapses and closely 
 allied to the substance of the motor end plate. Its similar nature 
 to the material of the motor end plate is suggested by the fact that 
 injections of adrenalin act variously on skeletal muscle, forming 
 a marked contrast to barium, which stimulates every skeletal 
 muscle fiber in the body, acting upon them directly. 
 
 The Facts Indicating the Nature of an Excitatory Process 
 By the following facts the nature of an excitatory process in nerves 
 is indicated: 
 
 (1) The dependence of irritability of a nerve upon a supply 
 of oxygen demonstrating that there is an expenditure of energy 
 even though in medullated fibers evidence of fatigue is absent. 
 It is impossible to estimate any dissipation of energy in the form 
 of heat. Non-medullated fibers can be fatigued. 
 
 (2) The failure of the decrement in the excitatory process as 
 it becomes transmitted. 
 
 (3) The excitatory state is attended with an electrical change 
 
 106 
 
THE NERVOUS SYSTEM 
 
 of such a nature that an excited spot is negative to all other 
 spots. The electrical change rises to a maximum rapidly and dies 
 away slowly. The amount of rise and fall is dependent upon the 
 tissue under investigation. 
 
 (4) The excitatory change is aroused only at the poles of a 
 current passing through the tissue, i.e., at the places where the 
 collection of ions is greatest. 
 
 (5) Excitation occurs only at the cathode at the make and, 
 only, if the current attains sufficient strength within a certain 
 length of time. 
 
 (6) All living tissues are made up of colloids divided into 
 compartments by membranes of various permeabilities and perme- 
 ated with salts and various electrolytes in solution. Very many 
 possibilities, therefore, exist for the formation of successive com- 
 partments characterized by large differences in potential. We 
 may conceive of a successive transmission of such electrical states, 
 and of such a movement of the ions, along a successive series of com- 
 partments in a nerve fiber as will account for large differences in 
 potential. The process may be roughly likened to the explosion 
 of a successive chain of equal masses of gunpowder. The number 
 of variables affecting the movement of the ions are numerous and 
 will permit of many possibilities. 
 
 108 
 
II 
 THE SPINAL CORD 
 
 MORPHOLOGY 
 
 Its Structure from a Development Standpoint In certain 
 orders of invertebrates the whole central nervous system is com- 
 posed solely of ganglia united by nerve strands. These simpler 
 nervous systems are, therefore, segmental in character. Even in 
 the embryo of mammals the first traces of the nervous system are 
 segmental. In the fully developed nervous system of mammals all 
 trace of the segmental character of the nervous system is lost 
 except as it is represented by the regular manner in which the 
 spinal nerves leave the spinal cord. 
 
 Gross Anatomy of the Spinal Cord The spinal cord is ap- 
 proximately eighteen inches long. (Fig. 58.) From its lateral 
 surfaces are given off thirty-one pairs of nerves. Each pair is com- 
 posed of an anterior and posterior root which emerges from the 
 spinal canal through the intervertebral foramen. On each posterior 
 root, before it joins the anterior root in its passage through the 
 intervertebral foramen, is a large ganglion through which the pos- 
 terior root passes. The anterior roots arise by a series of fasciculi 
 spread out over a rather considerable length of the particular level 
 of the cord from which the root arises. The posterior root arises 
 as a single well-marked bundle. 
 
 On section of the cord it is seen to be composed of a peripheral 
 white substance and a central gray substance. The central gray 
 substance is shaped somewhat like an H, and possesses in other 
 words two anterior horns and two posterior horns connected with 
 a transverse bar of gray matter. (Fig. 59.) In the center of this 
 transverse bar is a central canal. The white matter owes its color 
 to the fact that it is composed of medullated nerve fibers. The gray 
 matter is darker because within it are contained the nerve cells of 
 the spinal cord. Each lateral half of the spinal cord is separated 
 
 110 
 
THE NERVOUS SYSTEM 
 
 Middle ' 
 peduncle. 
 Inferior 
 peduncle. 
 
 VII. 
 
 VIII. 
 
 Superior peduncle of 
 
 the cerebellum. 
 Sulcus longitudinalis 
 
 medius. 
 
 Glosso-pharyngeal. 
 Vagus. 
 
 Spinal accessory. 
 
 Ligamentum denticula- 
 tum. 
 
 Posterior longitudinal 
 fissure. 
 
 An anterior root. 
 A posterior root. 
 
 XII. 
 
 L. I 
 
 S. I 
 
 Ganglion on 
 a posteri- 
 or root. 
 
 Fig. 58. Dorsal aspect of the medulla oblongata and spinal cord with the dura 
 mater partially removed. (Morris.) 
 
 112 
 
THE NERVOUS SYSTEM 
 
 114 
 
THE NERVOUS SYSTEM 
 
 from the other by a deep anterior and posterior fissure which 
 reaches nearly to the central transverse bar of gray matter. At the 
 bottom of these fissures are strands of transverse white fibers. 
 These are the anterior and posterior commissures. The amount 
 
 of central gray matter at any 
 level of the spinal cord is in 
 proportion to the number of 
 nerve fibers coming off at that 
 particular level. The amount 
 of white matter diminishes 
 progressively from above 
 downwards. The size of the 
 transverse section of the cord 
 is greatest in the cervical re- 
 gion, that region supplying 
 the upper limbs and contain- 
 ing all the fibers in the white 
 matter to and from the dorsal 
 and lumbar regions as well. 
 
 The cord is smallest in the 
 dorsal region and again en- 
 larges in the lumbar region 
 though smaller here than in 
 the cervical region. The en- 
 largement in the lumbar re- 
 gion is dependent entirely 
 upon the large amount of 
 gray matter, the axons of 
 which supply the lower limbs. 
 (Fig. 60.) 
 
 The Group of Nerve Cells 
 The nerve cells of the gray 
 matter are collected into cer- 
 tain groups. (Fig. 61.) Of the anterior horn there are : 
 
 1. A median group. Many of the processes of this group cross 
 the middle line. 
 
 2. An external group of large multipolar cells whose axons 
 enter directly the anterior nerve roots. 
 
 3. At the base of the anterior horn, in a region which may be 
 
 116 
 
 Fig. 60. Sections of spinal cord in lower 
 cervical, mid-thoracic, and mid- 
 lumbar regions. (Quain.) 
 On the right side of each section con- 
 ducting tracts are indicated. P.-M! (in 
 the lumbar region) , septo-marginal tract. 
 
THE NERVOUS SYSTEM 
 
 termed the lateral horn, is a group of small cells whose fibers 
 also enter the anterior nerve roots, forming the smaller nerve fibers 
 of these roots and belonging to the sympathetic nervous system. 
 
 4. In the posterior horn the nerve cells are more scattered but a 
 very well-marked collection of cells exists at the root of the pos- 
 terior horn near its in- 
 ternal side. It is known 
 as Clark's column of 
 cells. 
 
 The cells of the gray 
 matter of the spinal cord 
 may be classified from 
 their functional stand- 
 point as : 
 
 1. Motor cells, chief- 
 ly the a n t e r o-lateral 
 cells and the cells of the 
 anterior horn. 
 
 2. Cells of the col- 
 umns. The cells of 
 Clark's column, because 
 their axons form a defi- 
 nite column in the lat- 
 eral regions of the white 
 matter of the spinal 
 cord. 
 
 3. Commissural cells 
 whose axons cross to the 
 opposite side of the cord. 
 
 4. Cells of Golgi, 
 represented by a large 
 
 number of the cells of the posterior horn which are multipolar 
 and whose axons do not travel far from the cell but rapidly break 
 up into dendrites. They are, therefore, chiefly associative in 
 function. 
 
 Significance of the Connections of the System of Neurons 
 For a proper understanding of the functions of the spinal cord a 
 knowledge of the connections of the tracts which form systems of 
 neurons is absolutely essential. 
 
 118 
 
 Fig. 61. Diagram showing on the right side 
 the "ascending" and on the left side the 
 
 "descending" tracts in the spinal cord. 
 1, Crossed pyramidal; 2, direct pyramidal; 
 3, antero-lateral descending; 3a, bundle of 
 Helweg; 4, prepyramidal ; 5, comma; 6, pos- 
 tero-mesial; 7, postero-lateral ; 8, marginal; 
 9, dorsal cerebellar; 10, antero-lateral ascend- 
 ing or ventral cerebellar; s-m, septo-marginal ; 
 s.p.L, superficial postero-lateral fibres (dorsal 
 root-zone of Flechsig) ; o to a 5 , groups of cells 
 in the anterior horn; i, intermedio-lateral 
 group or cell-column in the lateral part of the 
 grey matter; p, cells of posterior horn; d 
 dorsal nucleus or cell-column of Clark. The 
 dots represent "endogenous" fibres (arising in 
 grey matter of cord) having for the most part 
 a short course. 
 
THE NERVOUS SYSTEM 
 
 Methods for Tracing the System of Neurons 
 
 a. By intravital staining. 
 
 &. By the impregnation method of Golgi. This method accom- 
 plishes the impregnation of the neurons by a 
 silver salt which blackens on exposure to light. 
 The feature which makes this method of value 
 is the fact that the impregnation is not general. 
 In virtue of this fact sections of considerable 
 thickness, containing a long distance of any 
 nerve fiber, may be studied. 
 
 c. Myelination Method As the nervous 
 system develops the nerve fibers become inclosed 
 in their myelin sheaths. The various systems of 
 neurons do not acquire their sheaths at the same 
 period. The tracts, which develop phylogeneti- 
 cally later, that is the youngest tracts, acquire 
 their myelin sheaths later and may hence be 
 recognized by stains which bring out the myelin 
 sheath, such stains when applied at an early 
 period of their development failing to render 
 them conspicuous as compared to the other sur- 
 rounding tracts. 
 
 d. The Walletian Method A nerve fiber 
 which is divided degenerates away from the 
 nerve cell of which the fiber may be an axon. 
 Whole tracts of nerve fibers may, therefore, de- 
 generate when they come from the same area of 
 gray matter. (Fig. 62.) As a result of this 
 degeneration fatty products are formed in the 
 myelin sheath of the degenerated nerves which 
 take an intense black stain with osmic acid. At 
 a period of three weeks after the tract has been 
 divided it will appear black; at the end of six 
 months these products will be removed and the 
 degenerated tract will take no stain at all. At 
 this stage it will also contrast strongly with the 
 
 undegenerated tracts which stain normally. (Fig. 63.) 
 
 e. Method of Retrograde Degeneration If an axon is divided 
 at a point distal to its cell, a certain degree of degeneration will 
 
 120 
 
 Fig. 62. Diagram 
 showing the de- 
 scending degen- 
 eration of the 
 pyramidal tract 
 following a le- 
 sion in the left 
 c e r e b r o hemi- 
 sphere involving 
 the Rolandic 
 area. 
 
 
THE NERVOUS SYSTEM 
 
 appear in the cell for a period of a few weeks, after which such a 
 cell will again regain its normal staining power. 
 
 vn. 
 
 vm. 
 
 Fig. 63. Diagram of sections of the spinal cord of the monkey, showing the 
 position of degenerated tracts of nerve-fibres after specific lesions of the 
 cord itself, of the afferent nerve-roots, and of the motor region of the cere- 
 bral cortex. The degenerations are shown by the method of Marchi. The 
 left side of the cord is in all cases on the reader's left hand. (Quain.) 
 
 I. Degenerations resulting from extirpation of the motor area of the cor- 
 tex of the left cerebral hemisphere. 
 
 II. Degenerations produced by section of the dorsal longitudinal bundles 
 in the upper part of the medulla oblongata. 
 
 III. and IV. Results of section of dorsal roots of the first, second, and 
 third lumbar nerves on the right side. III. is from the segment of cord be- 
 tween the last thoracic and first lumbar roots; IV. from the same cord in the 
 cervical region. 
 
 V. to VIII. Degenerations resulting from (right) semi-section of the cord 
 in the upper thoracic region. V. is taken a short distance above the level of 
 section; VI. higher up the cord (cervical region); VII. a little below the 
 level of section; VIII., lumbar region. 
 
 122 
 
THE NERVOUS SYSTEM 
 
 The same degenerative changes may, however, appear in a 
 motor cell from a section of posterior nerve root. Retrograde de- 
 generation is probably, therefore, a degeneration of disuse and must 
 be used in the tracing out of nerve tracts with much caution. 
 
 PHYSIOLOGY 
 
 THE EFFERENT AND AFFERENT PATHS TO AND FROM THE CORD 
 
 The Functions of the Anterior Nerve Roots and Method of 
 Investigating Them If the anterior nerve root is divided there 
 will result a paralysis of certain muscles. If the central end of 
 the root is stimulated no effects will be produced. If, on the other 
 hand, the peripheral end is stimulated certain muscles will con- 
 tract. 
 
 If the anterior root is one of the thoracic roots, certain visceral 
 effects will be produced by peripheral stimulation. Dilatation of 
 the pupils, or constriction of certain blood vessels, or augmentation 
 of the heart beat, are among these visceral effects. 
 
 The Functions of the Posterior Roots Division of one pos- 
 terior nerve root will usually produce no noticeable effect. Stimu- 
 lation of its peripheral end is also without effect. 
 
 Stimulation, however, of its central end in the conscious animal 
 will produce signs of pain. If the spinal cord has been divided 
 beneath the brain, central stimulation will produce reflex move- 
 ments. If two or three posterior nerve roots have been divided 
 there will be anesthesia over limited areas of the surface. 
 
 The anterior roots must, therefore, be regarded as entirely 
 efferent in their function, i.e., as the pathway out from the spinal 
 cord, the posterior roots as entirely afferent and the pathway into 
 the spinal cord. 
 
 The Peripheral Distribution of the Anterior Roots, and the 
 Function of the Plexuses Each muscle of the limbs receives 
 nerve fibers from more than one segment of the spinal cord. Hence 
 stimulation of one anterior nerve root in a peripheral direction 
 does not produce contraction of any one muscle or one physiological 
 group of muscles. The anterior nerve roots passing from that 
 region of the spinal cord which supplies the limbs unite after leav- 
 ing the spinal cord to form plexuses. From these plexuses the 
 
 124 
 
THE NERVOUS SYSTEM 
 
 single nerves come off which supply groups of muscles which are 
 physiologically related. 
 
 Stimulation of one of these nerves, therefore, causes a con- 
 traction of one muscle or one group of muscles which are physio- 
 logically related. 
 
 The Function of the Fine Fibers A section of a thoracic 
 anterior nerve root shows it to be composed of large and small 
 fibers. The large fibers are axons of the large cells in the lateral 
 region of the anterior horn and run to the muscles. 
 
 The fine fibers are axons of the cells in the lateral horns and 
 pass as the white rami communicates to the sympathetic system. 
 These fibers transmit impulses which cause dilatation of the pupils, 
 augmentation of the heart beat, contraction of the blood vessels, 
 inhibition of movements of the intestines and erection of hairs. 
 
 1. The Immediate Fate of the Fibers of the Posterior Nerve 
 Roots The fibers of the posterior roots pass directly into the 
 spinal cord, divide into an ascending bundle and descending 
 bundle. 
 
 (a) Lissauer's Column The descending bundle forms a tract 
 near the tip of the posterior horn. It is known as Lissauer's 
 column. The fibers of this tract are short and terminate in cells 
 in the substantia gelatinosa at the tip of the posterior horn. 
 
 (b) The Columns of Goll and Burdach The ascending fibers 
 are long. A large number of them pass upwards in the posterior 
 white columns of the cord, i.e., in the region between the posterior 
 horns and the posterior median fissure. In these columns the fibers 
 ascend through the whole length of the cord, and as they ascend 
 they occupy a more median position, making room in this manner 
 laterally for other fibers entering at higher levels. (Fig. 64.) The 
 external half of this posterior column is called the column of Bur- 
 dach, the internal bundle is called the column Goll. Both are well 
 marked in the cervical region. Other ascending fibers terminate at 
 different levels of the spinal cord around cell in the posterior horn. 
 All of the long fibers give off collateral fibers to cells at different 
 levels of the spinal cord. The fibers forming these long tracts are 
 the most internal of the fibers of the posterior root. 
 
 (c) Fibers ending in the cell tracts of the gray matter. These 
 fibers occupy a position in the posterior root between the fibers 
 of the long posterior columns and those of Lissauer's column. 
 
 126 
 
^ 9-il i 
 
 i linn 
 
THE NERVOUS SYSTEM 
 
 Five groups are traceable. (Figs. 64, 66, 67 and 68.) 
 
 1. Fibers to the cells of the posterior horn of the same side. 
 
 Fig. 65. Cross-sections of the spinal cord of the dog revealing the position 
 of the nerve-tracts descending to the hind-limb region from origin in the 
 foremost three thoracic segments, by the method of "successive degenera- 
 tion." 
 
 The eighth cervical segment had been exsected and 568 days later a crosscut 
 was made at the hindmost level of the third thoracic segment. The trans- 
 verse extent of this lesion, as determined by microscopic sections afterwards, 
 is shown in diagram 1 of the figure. The greater part of the right lateral 
 column is seen to have been spared from injury. Three weeks subsequent to 
 this second lesion the animal was sacrificed. Preparations made with the 
 Marchi method for revealing degenerate nerve fibres showed the degeneration 
 indicated by diagrams 2, 3, 4 and 5 in the figure. After the second injury to 
 the cord the scratch-reflex remained elicitable from the right shoulder, but 
 was lost from the left shoulder in its anterior scapular region. The degenera- 
 tion of these proprio-spinal fibres descending from the shoulder segments went, 
 therefore, hand in hand with disappearance of the scratch-reflex from a region 
 of skin of the shoulder whence it was elicitable previously. (Sherrington.) 
 
 130 
 
Fig. 66. Diagram representing the manner of origin or termination of the 
 roots of the spinal nerves in the gray matter substance of the spinal cord. 
 The distribution of the cells of the gray matter and the tracts of nerve 
 fibres in the white substance of the spinal cords: 
 
 1. THE ROOTS 
 
 r, the cells ; ra, the fibres of the .anterior nerve roots ; rpe, external trunk ; 
 rpi, internal trunk of a posterior nerve-root with, n, collaterals going to a 
 posterior external group of cells of the anterior horn and, r, to a group an- 
 terior to the latter; ss, to posterior horn cells, and, t, to the column of Clark. 
 
 2. THE GRAY MATTER 
 
 a, cells of the lateral column; b, cells of the posterior column; c, cells, the 
 axons of which cross the white commissure; cp. posterior commissure; d (in 
 the substance of Rolando), cells of Golgi with short axons; k, cells, the axons 
 of which cross the posterior commissure and go to the posterior horn of the 
 opposite side; r, cells, the axons of which turn back into the posterior root 
 zone. 
 
 3. COLUMNS OF THE WHITE MATTER 
 
 al, antero-lateral column or the column of Gowers; am, antero-marginal 
 column or the column of Loewenthal; bpa, bpm, brs, median portion, antero 
 and posterior columns of Burdach; cl, direct cerebellar tract; jb, continuation 
 of the posterior longitudinal bundle; jbl, fibres of the lateral column; fga, 
 fibres descending possibly from the anterior corpora quadrigemina, and pass- 
 ing across the base of the commissure; fl, fibres of the olivo-spinal tract; fla, 
 fibres of the anterior columns; jp, fibres of the antero-internal column; ft, 
 fibres of the prepyramidal tract of Monokaw; gi, portion of the column of 
 Goll contiguous to the dorsal septums; gl, intermediate zone of the posterior 
 column; i, fibres of the median or deep lateral column; I, fibres coming from 
 the lateral column and terminating in the anterior horn; m, fibres from the 
 anterior root zone; n, fibres from the deep column terminating in the pos- 
 terior horn; p lateral pyramidal tract containing two kinds of fibres; p, an- 
 tero-pyramidal tract; cp, ventral zone of the posterior tract; z, external or 
 marginal root zone. 
 
 132 
 
THE NERVOUS SYSTEM 
 
 2. Fibers to the cells of the posterior horn of the opposite 
 side. 
 
 3. Fibers to the median group of cells of the anterior horn. 
 
 4. Fibers to the cells of Clark's column. 
 
 5. Fibers to the motor cells of the anterior horn. 
 Significance of the Distribution of the Fibers of the Posterior 
 
 Nerve Roots Means, therefore, exist by which an incoming im- 
 pulse may pass upward for the whole length of the spinal or down- 
 wards or upwards for several or many segments of the spinal cord 
 or to a number of different groups of nerve cells within the gray 
 matter. 
 
 2. Inter segmental Filters and Their Positions (Fig. 65) The 
 fibers passing between different segments of the spinal cord are of 
 much importance. Within the white matter of the spinal cord they 
 occupy the following regions : 
 
 a. In the lateral columns immediately outside the central gray 
 matter in the concavity formed by the two horns. 
 
 6. Close to the gray matter in the anterior basic bundle. 
 
 c. In the posterior columns the following three situations : (1) 
 Close to the tip of the posterior horn. (2) A small area between 
 the columns of Goll and Burdach the comma tract. (3) Close to 
 the posterior fissure, the septomarginal bundle. 
 
 d. Mingled with the fibers of the pyramidal tract. 
 
 CONDUCTING FUNCTIONS OP THE SPINAL CORD 
 
 The Spinal Tracts Functionally similar nerve fibers within 
 the spinal cord are seldom isolated. Almost all run in bundles with 
 other fibers serving the same functions. Practically all nerve fibers 
 within the cord are connected by means of collateral fibers with 
 nerve cells of more than one segment. These collateral fibers, unlike 
 their parent fibers, which are medullated, have no medullary sheath. 
 The single axis cylinder lies embedded in a layer of myelin sur- 
 rounded immediately by neuroglia. 
 
 The various bundles of the spinal cord may be divided into : (1) 
 Proprio-spinal or internuncial fibers, fibers connecting various 
 levels of the spinal cord, some of which are ascending and others 
 descending. (2) Ascending bundles. (3) Descending bundles. 
 
 134 
 
THE NERVOUS SYSTEM 
 
 Some of the proprio-spinal tracts have already been considered. 
 Inasmuch as they are both ascending and descending we will de- 
 scribe them together with the ascending and descending tracts. 
 (Figs. 61, 65 and 67.) 
 
 Descending Tracts Pyramidal Tracts Found immediately 
 in front of the base of the posterior horns. It contains fibers which 
 originate in the nerve cells of the motor area of the cerebral cortex 
 and run without interruption through the cerebral peduncles, 
 through the pons Varolii, and through the medulla, where they 
 decussate with each other to gain the opposite side to enter the 
 pyramidal tract of the spinal cord and terminate by a terminal 
 arborization probably directly around the motor cells of the anterior 
 horns of the cord. By collaterals they communicate with the cells 
 of several levels. 
 
 The Prepyramidal Tract Situated in the spinal cord immedi- 
 ately in front of the pyramidal tract. It begins in the red nucleus 
 of the mid brain. The tract very probably represents an indirect 
 cerebellar spinal tract, in other words it continues the efferent im- 
 pulses from the cerebellum through the superior peduncles through 
 the red nucleus to the spinal cord. 
 
 The Vestibulo-Spinal Tract This tract establishes connections 
 between the higher equilibrium centers and the spinal cord. It 
 begins in the cells of Deiter's nucleus of the medulla, which is an 
 important substation to the cerebellum. The fibers of the vestibulo- 
 spinal tract are scattered in the antero-lateral column. 
 
 The Olivo-Spinal and Thalamo-Spinal Situated opposite the 
 tip of the anterior horn. It begins in the optic thalamus and in 
 cells of the inferior olivary body. The latter may be regarded as a 
 substation for many of the fibers between the thalamus and the 
 cord. 
 
 Tract of Marie A proprio-spinal tract, serving the same pur- 
 pose as the posterior longitudinal bundle to be studied later in the 
 brain. Its fibers are both ascending and descending and scattered 
 in the anterior columns. 
 
 Comma Tract In the interval between the columns of Burdach 
 and Goll, chiefly descending branches of the entering posterior 
 spinal nerves. 
 
 Septo-marginal Chiefly proprio-spinal, and situated adjacent 
 to the posterior portion of the posterior fissure. 
 
 136 
 
THE NEEVOUS SYSTEM 
 
THE NERVOUS SYSTEM 
 
 Ascending Tracts Posterior Columns Divided into the col- 
 umn of Burdach, the postero-lateral, and the column of Goll or 
 postero-median. The fibers of the posterior columns are derived 
 from ascending divisions of the entering posterior nerve roots. As 
 these enter they occupy first the postero-lateral column but become 
 displaced internally by similar fibers entering at higher levels. 
 Therefore the column of Burdach of the lumbar region becomes the 
 column of Goll in the cervical region. In the cervical region the 
 column of Goll contains fibers from the lower extremities and the 
 column of Burdach the fibers from the upper extremity. They 
 terminate in the medulla around cells of the nucleus cuneatus and 
 nucleus gracilis. 
 
 The Direct or Dorsal Cerebellar Tract Situated just anterior 
 to the outer extremities of the posterior horns, external to the 
 pyramidal tract. It may be viewed as one of the two afferent spino- 
 cerebellar tracts. Its fibers originate as axons of the cells of Clark 's 
 column, and run up to the corpus restiforme, then entering the 
 inferior cerebellar peduncle. 
 
 The Anterior or Ventral Cerebellar Tract Situated anterior 
 to the dorsal cerebellar tract, between it and the bundle of Helweg. 
 It ascends through the medulla to join the superior cerebellar 
 peduncle, by which it enters the cerebellum, to end in the cells of 
 the ventral nuclei of the superior worm. Inasmuch as this tract 
 does not increase in size, as it ascends, some of its fibers may join 
 the dorso-cerebellar tract or end in the cord. 
 
 Spino-Thalamic Situated just internally to the anterior cere- 
 bellar fibers, forming a tract which is often described as one tract 
 with the anterior cerebellar tract the tract of Gowers. It ter- 
 minates in the cells of the anterior corpora quadrigemina, but 
 chiefly in the cells of the optic thalamus. 
 
 Proprio- Spinal Fibers Chiefly the ascending fibers of the 
 tract of Marie in the antero-lateral column. 
 
 Functions of the Various Tracts Motor impulses descend 
 through the pyramidal tracts, and the indirect or crossed pyramidal 
 tracts, immediately lateral to the anterior fissure. 
 
 Impulses of pain both superficial and deep enter through the 
 posterior roots, cross immediately to the other side of the cord and 
 ascend in the internal portion of Gowers' tract to the optic thala- 
 inus. (Fig. 68.) 
 
 140 
 
THE NERVOUS SYSTEM 
 
 Impulses of heat and cold follow the same course. 
 
 Impulses of touch and pressure cross, after running upwards 
 for a few segments of the cord, to the other side of the cord and 
 ascend to the optic thalamus in the antero-lateral column. Some of 
 the fibers of cutaneous touch particularly those of tactile discrim- 
 
 AO 
 
 ALS 
 Fig. 68. The course of the fibres composing the posterior root. 
 
 I. The fibres of the posterior columns. 
 
 II. Fibres making connection with Clark's column and continued upward 
 in the posterior cerebellar tract, P. C. 
 
 III. IV, and V. Fibres forming connection with posterior horn cells and 
 continued upward in the anterior cerebellar tract, AC, conveying heterolat- 
 eral unconscious afferent impulses of muscular coordination and reflex tone. 
 G., Gowers' column transmitting impulses of pain, heat and cold. A.L.S., 
 Antero-lateral ascending sensory tract conveying impulses of touch and 
 pressure. 
 
 ination travel upwards uncrossed in the posterior columns. Con- 
 siderable evidence exists that touch impulses occupy a different 
 course than pain and temperature. We must regard superficial 
 touch sensations as compounded of superficial tactile discrimina- 
 tion and superficial pressure sensation. In the disease of syringo- 
 myelia, the senses of temperature and pain are affected while the 
 sense of touch is not. Moreover unilateral section of the cord does 
 
 142 
 
THE NERVOUS SYSTEM 
 
 not completely abolish the sense of touch on the same side below the 
 level of the lesion. 
 
 Impulses of muscular sensibility may be divided into those 
 which reach consciousness and those which do not. The former are 
 all homolateral within the spinal cord and make up the posterior 
 columns. The latter are partly homolateral, forming the direct or 
 posterior cerebellar tract, and partly heterolateral, forming the 
 anterior cerebellar tract. 
 
 Unilateral section of the Cord will produce the following symp- 
 toms: 
 
 Motor paralysis below the site of the lesion upon the same side. 
 
 Partial loss of consciousness of the position of the limbs below 
 the site of the lesion on the same side. 
 
 Complete anesthesia below the level of the lesion on the opposite 
 side. There will be a preservation of sensations of touch and pres- 
 sure for four or five segments below the level of the lesion on the 
 opposite side. There will be slight anesthesia for a narrow strip at 
 the level of the lesion on the same side. This narrow zone will be 
 above a hyperaesthetic zone. 
 
 There will be a paralysis of the vaso-motor nerves below the 
 level of the lesion on the same side. Vasomotor impulses travel 
 down the cord from the medulla on the same side. 
 
 SPINAL FUNCTIONS 
 
 For the study of the functions or reactions of the spinal cord 
 a study of the cord separated from the brain furnishes much valu- 
 able information. We are then able to study what may be termed 
 pure spinal reactions, reactions uninfluenced by impulses contin- 
 ually descending from above. An animal in which the spinal cord 
 has been severed from the brain is called a spinal animal. 
 
 Spinal shock is the first effect of dividing the spinal cord. 
 There is a great fall in the blood pressure and absolute paralysis 
 of the skeletal muscles and of the sphincters and abolition of all 
 reflexes. 
 
 The shock appears to only exist aboral to the plane of section. 
 In monkeys, for instance, after section of the cord below the cer- 
 vical region, though there is a fall of blood pressure and paralysis 
 of the trunk and lower extremities, nevertheless all muscles sup- 
 plied by nerves issuing from the cord above the plane of section 
 
 144 
 
THE NERVOUS SYSTEM 
 
 are active. Immediately after the section the animal will gaze 
 out of the window in a contented manner and even catch at flies. 
 After a period, which is proportional to the height in the scale 
 of life which the animal occupies, recovery from the shock occurs. 
 Permanent paralysis of voluntary motion and loss of sensation 
 remains for all regions below the plane of section. 
 
 Fig. 69. Tracing of the flexion of 
 the hip in the "scratch-reflex." 
 The reflex is evoked by two sepa- 
 rate stimulations (unipolar faradiza- 
 tion) at points ten centimeters apart 
 on the skin surface. The upper sig- 
 nal shows the time of application of 
 the first stimulation, and the line 
 immediately below that the frequency 
 of repetition of the double induction 
 shocks of that stimulation. The low- 
 est line signals the time of applica- 
 tion of the second stimulation; the 
 frequency of repetition of the double 
 shocks in this stimulation was much 
 greater than in the other stimulation 
 and is not shown. At the top the 
 time is marked in fifths of seconds. 
 The moment of commencement of 
 the first stimulation is marked by an 
 abscissa on the base line. The pe- 
 riods of the two separate stimula- 
 tions overlap, the second beginning 
 a full second before the first ends, 
 but no interruption or increase of 
 the rate of rhythmic reflex-response 
 appears. (Sherrington.) 
 
 Recovery from the Shock From the shock, however, the 
 animal recovers. The blood pressure first rises to normal. The 
 sphincters become functional and the bladder and rectum capable 
 of emptying themselves. Finally muscular tone is regained and 
 coordinated movements (reflexes) may be excited by stimuli. The 
 first reflexes to reappear are .those dependent upon painful or 
 nocuous stimuli and later those reflexes depending upon stimula- 
 tion of nerve endings in the joints and end organs in the muscles. 
 
 Cause of Spinal Shock Spinal shock does not depend upon 
 
 146 
 
THE NERVOUS SYSTEM 
 
 the lowered blood pressure nor to the trauma of the operation. 
 Regions not in the shock above the plane of section are exposed 
 to the same lowered blood pressure and a second section below the 
 first, even if performed with little precaution to avoid trauma, 
 
 Fig. 70. Flexion-reflex. Spinal dog. Latent time of incremental reflex com- 
 pared with that of initial reflex. Unipolar faradization by break shocks. 
 
 Kathode at needle-point in plantar skin of outermost digit. 
 A weak initial stimulus is delivered and maintained, and then when the 
 resulting reflex movement has become steady the stimulus is increased in 
 intensity by short-circuiting 5 ohms from the primary circuit. The rate and 
 intensity of the break shocks are marked above by a recording electromagnet ; 
 the armature is arranged to have an ampler excursion when the current is 
 increased at the point marked B. The latent time of the incremental reflex is 
 seen to right hand, and is distinctly shorter than that of the initial reflex. 
 Time below is written in 1/100 sec. and in seconds. Abscissae on the myograph 
 line show the moment of first delivery of the initial (.4) and of the incre- 
 mental (B) stimuli. (Sherrington.) 
 
 does not add to the degree of shock. It is directly dependent upon 
 the cutting off of the normally descending impulses from higher 
 parts of the nervous system which, so to speak, keep the cord awake 
 and responsive. 
 
 Recovery from the shock depends upon the power of the spinal 
 centers to acquire a more independent activity of their own in 
 
 148 
 
THE NERVOUS SYSTEM 
 
 the absence of the assistance of the central nervous system. In 
 the dog recovery may even occur to such an extent that it may be 
 
 able to take a few steps if it be 
 raised and given a push, al- 
 though it cannot walk. 
 
 Swimming movements may 
 be carried out regularly. They 
 are not voluntary but purely re- 
 flex, the necessary sensory stimu- 
 lus being supplied by the exten- 
 sion of the muscles, and are of 
 the nature of alternate flexion 
 and extension in the hind limbs 
 when the animal is held upright 
 by his fore limbs. 
 
 A Study of the Spinal Re- 
 flexes Scratch Reflex Con- 
 tinued gentle stimulation over 
 the shoulders will cause rhyth- 
 mic flexion and extension of the 
 hind limb of the same side as 
 though making an attempt to 
 brush off the irritant. (Figs. 
 69-71.) 
 
 Sole Reflex Pricking the 
 sole of the foot will cause flex- 
 ion of the leg and thigh and, if 
 the stimulus is strong enough, 
 extension of the opposite leg. 
 
 Gentle pressure upwards 
 against the sole will cause ex- 
 tension of the same leg and flex- 
 
 
 Fig. 71. A, B, Scratch-reflex. 
 The tracings show the usual length- 
 ening of latency on reducing the in- 
 tensity of the stimulation. The two 
 tracings are in reproduction unequal- 
 ly reduced, but the frequency of 
 repetition of the double-induction 
 shocks used as stimuli was the same 
 in both shocks of weaker intensity in 
 B than in A. The reflex movement 
 began after delivery of three stimuli 
 in A, after delivery of nine in B. 
 The greater intensity of the stimuli 
 in A is also evidenced by the greater 
 amplitude of the movement and by 
 the longer "after-discharge." Time 
 marked in fifths of seconds below. 
 
 ion of the opposite leg. 
 
 Vascular Reflex A rise in 
 blood pressure may be obtained 
 from afferent stimulation of the 
 digital nerve. (Fig. 72.) 
 
 Bladder and rectal reflex is 
 the stimulus within the bladder 
 
 150 
 
THE NERVOUS SYSTEM 
 
 and rectum of urine and feces which will cause voluntary evacua- 
 tion of these organs. Even coitus and parturition may occur. 
 
 Muscular Tone The degree with which muscular tone can 
 return is illustrated in a frog which has recovered from spinal 
 shock by section of its posterior spinal nerves on one side. That 
 side will then be perfectly flaccid and completely extended con- 
 trasting with a partially flexed position of the other leg when the 
 animal is suspended. (Fig. 73.) In other words, after the recovery 
 
 from the shock stim- 
 uli are continually as- 
 cending to the spinal 
 cord from the muscles 
 themselves which ex- 
 cite other efferent 
 stimuli that keep the 
 muscles in some de- 
 gree of contraction. 
 The partial contrac- 
 tion, in other words, 
 the keeping the mus- 
 cles in a condition of 
 
 Fig. 72. Spinal vasomotor reflex; dog; 300 days wakefulness, is called 
 after spinal transection at eighth cervical level; 
 
 sp 
 
 chloroform and curare. Electrical stimulation 
 of central end of a digital nerve of hind limb 
 during the time marked by signal on second 
 line from bottom. The arterial pressure (caro- 
 tid) rises from 90 mm. Hg. to 208 mm. Hg. 
 Time marked below in 2 seconds. (Sherrington.) 
 
 tone. 
 
 Tendon Reflexes 
 The patella reflex is 
 only one of various 
 other tendon reflexes, 
 indeed the phenome- 
 It illustrates the factors determin- 
 
 non is common to all tendons, 
 ing muscular tone. 
 
 A tendon reflex may be elicited by tapping the tendon of a 
 limb placed in a flexed condition but preferably in such a position 
 that the tendon is somewhat on the stretch. For the right patellar 
 reflex the right knee should cross the left allowing the leg to hang 
 loosely over the left one. The patellar tendon is then sharply 
 struck. Immediately the quadriceps extension of the right limb 
 will contract, causing the leg to give a little jerk. The latent 
 period between the time of the blow to the tendon and the con- 
 traction is very short, according to Gotch only .005 of a second, 
 
 152 
 
THE NERVOUS SYSTEM 
 
 which is also the duration of the latent period when the vastus 
 internus is directly stimulated. 
 
 Manifestly, therefore, it must bu considered possible that the 
 cause of the knee jerk is the direct effect of tjie blow upon the 
 muscle, but this cannot be all. Section of the posterior nerve roots 
 of the third and fourth lumbar nerves will 
 abolish the knee jerk, so also stretching the 
 hamstring muscles or the antagonists of the 
 flexors or weak stimulation of the nerve sup- 
 plying hamstrings. 
 
 Section of the hamstrings or their nerve 
 will increase the knee jerk reflex. These facts 
 indicate that an afferent path to the spinal 
 cord is necessary for the elicitation of the ten- 
 don phenomenon, and also a relaxation of the 
 antagonists to the. muscles which produce the 
 contraction of the muscles which are con- 
 cerned in the tendon reflex in question. 
 
 In order to accomplish this relaxation, 
 a reflex arc through the spinal centers is nec- 
 essary, a fact also attested by the abolition of 
 the knee jerk in consequence of dividing the 
 posterior spinal roots. 
 
 It has been suggested that the part played 
 by the spinal cord is one merely maintain- 
 ing muscular tone, keeping, so to speak, the 
 muscles in a state of wakefulness. While this 
 suggestion may in a large part explain the 
 characters of the tendon reflex, it is not the 
 entire explanation. More accurate measure- 
 ments by Jolly of the current of action in 
 the muscles and nerves, with a sensitive gal- 
 vanometer, show in disagreement with the 
 conclusions of Gotch that the latent period 
 of the knee jerk contains also a small reduced 
 reflex time of .002 of a second, corresponding perhaps with only 
 one synapse. These measurements are as follows: 
 
 Fig. 73. Illustrating 
 the difference in the 
 tone of the legs of 
 a frog when the pos- 
 terior root nerves 
 of one side have 
 been divided. 
 
 154 
 
THE NERVOUS SYSTEM 
 
 Time of knee jerk 0053 
 
 Time in afferent ending 0004 
 
 Time in nerve conduction. 0014 
 
 Time in motor endings 0013 .0031 
 
 .002 + 
 
 Other examples of tendon reflexes are the Babinski sole reflex 
 and Koernig's sign. 
 
 These facts are all confirmed by certain pathological conditions 
 in man. 
 
 In locomotor ataxia, in which there is degeneration of the 
 posterior columns of the spinal cord containing the mechanism 
 for afferent impulses from the muscles, there is a loss of knee jerk. 
 In the disease lateral sclerosis, in which the pyramidal tracts are 
 degenerated, there no longer exists any controlling influence from 
 above upon the motor mechanism of the cord and the motor mech- 
 anism of the cord, as in recovery from spinal shock, assumes an 
 independent and exaggerated activity, consequently the knee jerks 
 are increased. 
 
 SUMMARY OF THE FUNCTIONS OF THE SPINAL CORD 
 
 The spinal cord must, therefore, be viewed as a part of a mech- 
 anism for obtaining a certain definite coordinated response of a 
 limited segmental character from certain peripheral stimuli and 
 for maintaining, as a result of certain deep seated stimuli, a mus- 
 cular tone in the skeletal muscles. It also maintains a tone in 
 certain of the vessels and structures within the body cavities con- 
 veniently though not accurately described as visceral tone. 
 
 The maintenance of both the skeletal tone and visceral tone is 
 part of a reflex mechanism and is absent in the absence of the 
 necessary afferent impulses or is changed with a change in the 
 normal relation of excitatory or inhibitory impulses from above 
 or from other parts of the nervous system. 
 
 The Characteristics of a Spinal Reflex Purpose-like Every 
 reflex movement may be described as a purpose-like movement for 
 the simple reason that every reflex is an action frequently used by 
 the animal. This fact constitutes the reason why during the process 
 
 156 
 
THE NERVOUS SYSTEM 
 
 of development the various neurons are so connected that the 
 various reflexes become possible. The word purpose-like has been 
 used instead of purposeful because every reflex act is at the same 
 time fateful. 
 
 Fig. 74. A: The "receptive field," as revealed after low cervical transection, 
 a saddleshaped area of dorsal skin, whence the scratch-reflex of the left 
 hind limb can be evoked. Ir marks the position of the last rib. 
 
 B: Diagram of the spinal arcs involved. L, receptive or afferent nerve-path 
 from the left foot; R, receptive nerve-path from the opposite foot; Ra, Rb, 
 receptive nerve-paths from hairs in the dorsal skin of the left side; FC, 
 the final common path, in this case the motor neurone to a flexor muscle 
 of the hip; Pa, Pb, proprio-spinal neurones. (Sherrington.) 
 
 Fateful The spinal cord, unless inhibited by actions of the 
 higher nervous system, always responds in a definite calculable 
 manner. The beheaded eel will wind itself around a red hot poker. 
 The beheaded snake will spring back to any agent grasping its 
 tail. 
 
 158 
 

 
 t* ac. S .2 i" 
 
 C O 
 
 ,2 a 
 
 8 H G 
 
 160 
 

THE NERVOUS SYSTEM 
 
 Pleurisegmental All reflex movements are such as would 
 under usual conditions perform useful acts for the animal, and all 
 are complicated, involving several segments of the spinal cord. 
 They are all pleurisegmental (see Fig. 74). 
 
 Capable of Spreading The plantar or sole reflex in the mam- 
 mal not only involves the extremity on the side of the provoked 
 sensory stimulus hut may also involve the extremity of the other 
 side. 
 
 The spreading of the response is always in a definite order 
 called irradiation, and just what response is called forth is deter- 
 mined hy the place or locus of the peripheral stimulus. We have 
 thus far only spoken of the contraction of certain sets of muscles 
 in the description of this response, hut the contracting muscles are 
 only half of those which participate in the reflex act. 
 
 Capable of Inhibition No reflex can effectively take place 
 without the simultaneous relaxation of the set of muscles antagon- 
 istic to those which are undergoing contraction. During the re- 
 flex withdrawal of one foot (flexion) and extension of the oppo- 
 site leg, there is not only contraction of the flexors but also relaxa- 
 tion of the extensors on the one side and contraction of the exten- 
 sors and relaxation of the flexors on the other side. This relaxa- 
 tion is accomplished by impulses which inhibit centrally the im- 
 pulses responsible for the normal muscular tone of the relaxing 
 muscles. The relaxation may be 'measured by a recording instru- 
 ment which demonstrates the actual lengthening of the muscle. 
 
 A reflex action may be altogether prevented by influences 
 transpiring in other portions of the central nervous system. Any 
 inhibition is accomplished by nerve fibers running to the central 
 synapses of the reflex in question from the other portions of the 
 nervous system. Certain reflexes are prepotent; others may be 
 made prepotent by strong stimuli. Prepotent reflexes have a 
 tendency to inhibit other reflexes which may be transpiring. 
 The possibility of reinforcing the knee jerk reflex by pulling apart 
 the clasped hands illustrates the presence, normally, of constant 
 inhibitory impulses to the extensors of the thigh. If the reinforc- 
 ing act precedes the stimulation of the reflex by .06 sec. the inhibi- 
 tion begins to appear. 
 
 Capable of Prepotency Certain reflexes possess precedence 
 over others. Reflexes from painful or nocuous stimuli will proceed 
 
 162 
 
THE NERVOUS SYSTEM 
 
 in the place of other reflexes which may have been started. Only 
 one reflex can proceed at a time. The central nervous system only 
 attends to one thing at a time. A reflex in process of performance 
 will be checked by another reflex started by a 
 stronger stimulus. The checking process is 
 one of inhibition, but after the period of in- 
 hibition has passed the inhibited reflex will 
 proceed again with renewed vigor, as though 
 its stimulus during the period of inhibition 
 were really effective though apparently only 
 accumulatively so. 
 
 Capable of Reenforcement If one reflex 
 is proceeding, another reflex giving rise to an 
 action cooperating toward the same end is 
 started, will proceed and strengthen the 
 first reflex. Strongly pulling the interlocked 
 fists apart will reinforce the knee jerk. 
 
 Capable of Fatigue Too frequent excita- 
 tion of a reflex causes fatigue at the central 
 synapse. If the stimulus exciting a reflex 
 which has been fatigued is moved only a very 
 slight distance to the side of the locus of 
 the reflex, it will again proceed with renewed 
 vigor. Therefore the most important site of 
 the fatigue must lie jn the synapse upon the 
 afferent side of the reflex arc. 
 
 Explanation of the "Mark Time" Move- 
 ment Just as repetition of a reflex causes 
 fatigue, so inhibition causes reenforcement of 
 a reflex. These two facts explain the auto- 
 matic swimming movement or the automatic 
 and continuous flexion and extension of first 
 one leg and then the other in the suspended 
 dog. The weight of one leg produces a stimu- 
 lus to the contraction of its flexors, accompanied by inhibition of 
 flexion upon the opposite side. This flexion is followed by slight 
 fatigue on the newly flexed side and a dropping of the inhibited 
 side, which in turn is stimulated by this drop or extension and, 
 in virtue of the rest during the previous period of inhibition, is 
 
 164 
 
 Fig. 75. Scratch-re- 
 flex interrupted by 
 a brief flexion-re- 
 flex. 
 
 The time of appli- 
 cation of the stimulus 
 evoking scratch-reflex 
 is shown by the low- 
 est signal line ; that of 
 the stimulus of the 
 flexion-reflex in the 
 signal line immediate- 
 ly above the other. 
 Time marked in fifths 
 of seconds at top of 
 the record. The 
 scratch-reflex returns 
 with increased inten- 
 sity after the inter- 
 ruption. (Sherring- 
 ton.) 
 
THE NERVOUS SYSTEM 
 
 in a condition to respond to the stimulus produced by its own 
 extension. This stimulus causes it to be flexed and the flexion in 
 the first limb to be inhibited in its turn. 
 
 In the excitation and control of reflex actions two varieties of 
 afferent impulses are concerned. One set of these impulses comes 
 
 Fig. 75 l /2. Diagram indicating connections and actions of two efferent root- 
 cells, a and a' in regard to their reflex influence on the extensor 
 
 and flexor muscles of the two knees. 
 
 a, root-cell afferent from skin below knee; a', root-cell afferent from flexor 
 muscle of knee, i.e., in hamstring nerve; e and e', efferent neurones to the 
 extensor muscles of the knee, left and right; s and s', efferent neurones to the 
 flexor muscles; E and E', extensor muscles; F and F', flexor muscles. The 
 "schalt-zellen" (v. Monakow) probably between the afferent and efferent 
 root-cells are for simplicity omitted. The sign + indicates that at the 
 synapse which it marks the afferent fibre a (and a') excites the motor neu- 
 rone to discharging activity, whereas the sign indicates that at the synapse 
 which it marks the afferent fibre a (and a') inhibits the discharging activity 
 of the motor neurones. The effect of strychnine and of tetanus toxin is to 
 convert the minus sign into plus sign. (Sherrington.) 
 
 166 
 
THE NERVOUS SYSTEM 
 
 from the surface and may be termed exogenous afferent impulses. 
 The second set originate within the muscles themselves and within 
 the tendons and joints. They are the deep or endogenous impulses. 
 
 The first set are chiefly concerned in the excitation of reflexes. 
 The second set chiefly, though by no means exclusively, with the 
 degree with which the response to any particular reflex takes place 
 in the various muscles concerned. 
 
 In other words the second set of impulses guide or control the 
 response in such a manner that it is possible for it to become a 
 coordinated movement. It is through them that information is ob- 
 tained as to the degree of contraction of any muscle. 
 
 When these impulses are cut off the position of the limbs be- 
 comes abnormal. It is due to this fact that after the posterior nerve 
 roots of one hind limb of a frog have been divided the frog's limb 
 assumes a position of permanent extension and will hang with the 
 legs limp. 
 
 If all the posterior nerve roots of the cervical nerves of one side, 
 except the eighth, of a monkey are divided the monkey will still 
 use its arm for climbing, but the movements will be inexact. The 
 inexactness is chiefly in the arm. The hand, which is supplied by 
 the eighth cervical, exercises perfect precision. The monkey has 
 lost information from the muscles enabling it to know the various 
 degrees of contraction of the muscles of the arm. If the eighth 
 cervical nerve is then also divided, the arm will become totally 
 paralyzed. 
 
 Capable of Localization With the same certainty that a defi- 
 nite muscle contracts after the application of a stimulus to its motor 
 nerve, so the application of a stimulus to the peripheral ter- 
 mination of a sensory nerve will call forth, in the absence of in- 
 hibitory influences, a definite response. A fixed path of least re- 
 sistance for the propagation of the impulse to and through and 
 from the central nervous system has been developed. 
 
 Capable of Delay No response to a stimulus of a sensory 
 neuron is immediate. A delay exists which represents the time 
 necessary for the impulse to ascend the sensory neuron and for the 
 impulse to pass across the synapse in the central nervous system 
 and for the terminally provoked impulse, the efferent impulse, to 
 descend the motor or secretory nerve. 
 
 The speed of impulse along nerve fibers is known and the latent 
 
 168 
 
THE NERVOUS SYSTEM 
 
 period involved in the starting of the sensory impulse and in the 
 production of the effect by the efferent impulse, after the latter 
 has reached the peripheral termination of the efferent nerve, are 
 also known. When the time taken by these processes, which rep- 
 resents all the time of that portion of a reflex occurring outside 
 the central nervous system, is subtracted from the total time of 
 the simplest unilateral reflex act, there will be left over .008 of a 
 second. 
 
 This time, therefore, represents the time of that portion of a 
 reflex act which is occupied in the passage of its impulse across 
 the synapses in the central nervous system. It is called the reduced 
 reflex time. When the reflex is a crossed reflex the reduced reflex 
 time is .004 of a second longer. Probably two additional synapses 
 are involved in a crossed reflex, so that the time occupied in a 
 single synapse is about .002 of a second. 
 
 Capable of Summation To produce a reflex response by a 
 single stimulus that stimulus must possess a certain strength. A 
 weaker stimulus is a subminimal stimulus. A subminimal stimulus, 
 however, is not necessarily without effect, inasmuch as several, 
 five or six, subminimal stimuli applied at a proper interval will 
 result in a response. The term summation is applied to this phe- 
 nomenon. 
 
 Capable of Block Fatigue illustrates one form of block, 
 aamely, an increased resistance across a synapse. The existence 
 of a definite path for each reflex through the central nervous system 
 demonstrates the presence of increased resistance to that reflex in 
 all other synapses of the central nervous system. The reality of this 
 increased resistance is made more evident when it is dissipated by 
 the administration of strychnine or the tetanus toxine. 
 
 Capable of Facilitation Some resistance to the passage of an 
 impulse across the central synapse of a reflex exists even in that 
 synapse which belongs peculiarly to the reflex in question. This 
 resistance can be measured by the strength of current necessary to 
 provoke the reflex. It may be diminished by frequently provoking 
 the reflex at an interval not short enough to result in fatigue. 
 This diminution of resistance across a synapse by use is called 
 facilitation. Upon it depends the possibility of education and 
 memory. 
 
 The Nature of the Path Across a Synapse The transmission 
 
 170 
 
THE NERVOUS SYSTEM 
 
 of impulses so constantly in definite paths suggests the existence 
 of a direct connection across the synapse. Certain observers have 
 found good evidence of such direct connections among some of 
 the lower orders of invertebrates and have maintained that they 
 exist also throughout the nervous systems of -animals. By special 
 staining methods they have attempted to demonstrate actual con- 
 nections between the dendrites of a nerve cell at nodal points in 
 the terminal arborization of the afferent nerve fiber to this cell. 
 In fact, some preparations show that the terminal arborization 
 around a central nerve cell forms an actual basket of a netlike 
 structure closely surrounding the cell with enlarged nodal points. 
 Do the fibrillse of the nerve cell run out into the dendrites and 
 connect by means of them with these nodal points? The indirect- 
 ness of such a path through a synapse may account for certain 
 phenomena, such as delay existing at a synapse, but the law of 
 forward direction will ever constitute an objection to the existence 
 of a direct connection across a synapse. 
 
 There must exist a free ending to the dendrites of one neuron, 
 and a beginning to the dendrites of the neuron next in the chain, 
 and an interval filled with a different substance between the two. 
 
 Functions of the Various Portions of a Reflex Arc The func- 
 tion of the nerve fiber is solely one of conduction. We may exclude 
 excitation. 
 
 The function served by the synapse is also one of conduction. 
 
 What, however, is the function of the central nerve cell ? May 
 it originate impulses, or does it modify them, or does it solely 
 conduct them, and are there any other possible functions which it 
 may perform? 
 
 The Function of the Central Nerve Cell In answering this 
 question all the vital phenomena presented by living cells must 
 be considered. Foremost among these is the maintenance of nutri- 
 tion. We have seen that no cell is capable of continued existence 
 without a nucleus. The sole purpose for which the nervous system 
 has developed is one of communication. This is accomplished by 
 nerve fibers. Each nerve fiber which, in many instances^ consti- 
 tutes the major part of the neuron, would be without a nucleus 
 were it not for its attachment at one end to the nerve cell. 
 
 Trophic In fact, the nerve fiber may be viewed as a long and 
 permanent pseudopod of a nerve cell, and without attachment to 
 
 172 
 
THE NERVOUS SYSTEM 
 
 the cell will degenerate. An important function, therefore, of 
 the nerve cell is the nutrition of its nerve fiber. The adjective 
 trophic is the term which is used to describe this function. 
 
 Transmission Nerve cells must transmit impulses. Less cer- 
 tainty, however, attaches itself to the question whether nerve cells 
 modify impulses passing through them apart from other influences 
 reaching them or even whether they may be spoken of apart from 
 the fact that they are situated at a synapse as switch stations of 
 the nerve impulses. 
 
 Automaticity Much evidence exists that nerve cells do not 
 originate nerve impulses. In the absence of all afferent stimuli 
 they become functionless. Metabolic activity with the evolution 
 of energy transpires within them. The evidence of this is supplied 
 by the rapid loss of power to functionate in the absence of oxygen. 
 
 Clamping the aorta soon produces a paralysis of the whole 
 spinal cord. Nevertheless, in the same manner a lack of oxygen 
 will render nerve fibers incapable of conduction. 
 
 In some of the lower invertebrates the ganglion cells of afferent 
 fibers may be excised without injury to the terminal arborization 
 of the afferent and efferent nerve fibers to these cells and without 
 immediately influencing in any way the function of the concerned 
 neurons. So far, therefore, as the nervous activity of these cells 
 is concerned it is limited entirely to transmission and trophic func- 
 tions. Like other cells in the body the nerve cells have become 
 highly differentiated for the purpose of performing most effectively 
 one function. 
 
 This function is primarily one of reaction, a reaction which 
 includes two factors, excitability and conductivity. It is very 
 doubtful whether nerve cells possess any automatic function what- 
 soever. Even after large doses of strychnine have been adminis- 
 tered in the absence of all afferent impulses, a condition, for in- 
 stance, which exists after the section of all the posterior nerve 
 roots, a frog will lie absolutely motionless. 
 
 Such serious changes in respiration are induced after cutting 
 off all afferent impulses that it is possible that the demarcation 
 currents, due to the trauma of the cut nerves may account for the 
 incomplete and deficient respiration remaining after such an 
 experiment. 
 
 174 
 
THE NERVOUS SYSTEM 
 
 TROPHIC FUNCTIONS OP THE CORD 
 
 We have thus far considered only the motor and sensory func- 
 tions of the spinal cord. The spinal cord also exercises trophic 
 functions upon both the muscles and the skin. When its connec- 
 tions with the muscles are severed, the muscles concerned atrophy. 
 When the skin is separated by division of the posterior nerve roots 
 it also shows nutritional changes. The skin becomes scaly, glossy, 
 and the hair and nails show changes. When certain sensory nerves 
 become inflamed peculiar eruptions appear. One very characteris- 
 tic one is known in popular language as "shingles." The paths 
 exerting trophic functions only become active in post-fetal life. 
 During intrauterine life, even in complete absence of the nervous 
 system, the muscles develop normally. 
 
 176 
 
Ill 
 THE BRAIN 
 
 Development of the Brain Phylogenetically the brain is 
 changed anterior segments of the cerebrospinal axis having devel- 
 oped by alterations of nervous tissue similar in every way to the 
 separate segments of which the spinal cord in mammal is composed 
 and of which the more definitely segmental nervous system of the 
 lower animals is formed. The alterations are due to the addition 
 of new nerve tracts and new nerve centers. 
 
 The new nerve tracts connect the different portions of the brain 
 and the brain with the different segments of the spinal cord. The 
 new nerve centers serve as relay stations to the tracts connected 
 with them, making possible a modification of the afferent impulses 
 reaching them, by passing them on as efferent impulses altered 
 as to their destination or strength by a partial switching or by other 
 impulses also reaching these centers from other portions of the 
 nervous system upon other afferent tracts to these same centers. 
 
 The Three Primary Cerebral Vesicles After the primary 
 neural groove has been transformed into a tube at the head end, 
 three cavities become constricted off in such a manner as to par- 
 tially separate them. These three cavities are the three primary 
 cerebral vesicles, and it is from them that the three main divisions 
 of the adult brain develop. 
 
 From the anterior vesicle develops the forebrain or the prosen- 
 cephalon. It may be divided into the thalamencephalon, including 
 the subsequent cerebral hemispheres, the lateral ventricles, the 
 retina and the olfactory lobes, and the diencephalon which includes 
 the third ventricle and the optic thalami. (Figs. 76-77.) 
 
 From the middle cerebral vesicle, or the mesencephalon, develops 
 the corpora quadrigemina and the iter of Sylvius. From the hind- 
 brain, the rhomb encephalon, develops the cerebellum, the pons and 
 the upper half of the fourth ventricle, together constituting a sub- 
 
 178 
 
THE NERVOUS SYSTEM 
 
 division known as the myelencephalon, and the lower half of the 
 fourth ventricle known as the metencephalon.- 
 
 The retina of the eye is developed from two lateral, stalk-like 
 protrusions from the sides of the primary anterior cerebral vesicle. 
 
 Corpora quadrigemina. 
 
 Cerebell 
 
 Mesencephalon. 
 
 Pineal body. 
 
 Pons 
 varolii. 
 
 Crura cerebri. Optic thalamus. | Pituitary body. Foramen of Monro. 
 Thalamencephalon. 
 
 Fig. 76. Diagrammatic sagittal section of a vertebrate brain. (Morris.) 
 4, fourth ventricle; s, cerebral aqueduct; 3, third ventricle. 
 
 Each cerebral hemisphere also develops by a bud-like expansion of 
 the anterior extremity of the anterior cerebral vesicle. The bud 
 contains a cavity which permanently retains its connection with the 
 original cavity of the anterior cerebral vesicle. The growth of these 
 
 Epencephalon. Optic thalamus. 
 
 Cerebellum 
 
 Mesencephalon. 
 
 Foramen of Monro. 
 
 Fig. 77. Diagrammatic horizontal section of a vertebrate brain. 
 4, fourth ventricle; 3, third ventricle. 
 
 Corpus 
 striatum. 
 
 (Morris.) 
 
 buds is so excessive that they completely cover the sides and dorsum 
 of the rest of the brain. 
 
 The original cavity of the buds becomes the lateral ventricle and 
 its permanent connection with the cavity of the anterior cerebral 
 vesicle constitutes what afterwards becomes the foramen of Monro. 
 
 180 
 
THE NERVOUS SYSTEM 
 
 g 
 
 A comparison of a schematic representation of the primary cerebral 
 vesicles and the adult brain will make these facts evident, and will 
 clearly establish the relative positions of the various portions of the 
 adult brain. 
 
 Beginning at the transition between the spinal cord and the 
 brain and passing from below upwards, the central canal of the 
 spinal column opens out into the fourth ventricle of the brain. In- 
 cluding its pontine portion the latter measures nearly two inches in 
 length and about three-quarters of an inch in breadth at its widest 
 portion. Posterior to the medulla and forming a large portion of 
 the roof of the fourth ventricle is the cerebellum. 
 
 The cerebellum forms a large and separate division of the human 
 brain. It measures about four inches by two by one and a half. 
 The most prominent structures forming the lateral boundaries of 
 the fourth ventricle are the superior, middle and inferior peduncles 
 of the cerebellum. These are thick bundles of nerve fibers by which 
 the cerebellum is connected with the mid-brain, the medulla and the 
 spinal cord respectively. 
 
 The Fourth Ventricle The floor of the fourth ventricle con- 
 sists of gray matter, which, in this portion of the brain, represents 
 the gray matter of the spinal cord displaced posteriorly by the 
 opening of the central canal of the latter. 
 
 It is diamond-shaped and divided at its middle by transversely 
 running strands of nerve fibers, the strice acusticce, into an upper 
 pontine and a lower bulbar portion. On the floor of the bulbar 
 portion is a triangular depression, the ala cinerea, separating a 
 lateral triangular prominence, the tuberculum acusticum f from a 
 median prominence, the trigonum hypoglossi. (Fig. 78.) 
 
 The nucleus of the pneumogastric nerve forms the gray matter 
 of the ala cinerea. External to it is the nucleus of the eighth nerve. 
 It overlies the position of the more deeply placed Deiters' nucleus, 
 and extends up under the striae acusticae into the floor of the pon- 
 tine portion of the fourth ventricle. In this region it is separated 
 by a shallow depression from a more medially placed elongated 
 prominence, the eminentia teres. The eminentia teres is formed by 
 the gray matter of the nucleus of the sixth nerve. It corresponds 
 in its position above the striae acusticae to the trigonum hypoglossi 
 below, and its gray matter is the direct continuation of the gray 
 matter of the latter. 
 
 182 
 

THE NERVOUS SYSTEM 
 
 184 
 
THE NERVOUS SYSTEM 
 
 The Iter of Sylvius Passing further upwards in the exam- 
 ination of the brain, the cavity of the fourth ventricle becomes 
 again contracted into a narrow canal, the iter of Sylvius or the 
 Sylvian aqueduct, which runs between it and the third ventricle. 
 It is rather more than half an inch long. Like the central canal of 
 the spinal cord it is surrounded by gray matter. The gray matter 
 of its floor gives rise to the fourth and third nerves. 
 
 Four large nuclei, two upon each side of the middle line, cover 
 its roof. These are called the superior and inferior corpora quad- 
 rigemina. Each forms a prominent rounded eminence upon the roof 
 of the Sylvian aqueduct. The superior is intimately related with a 
 smaller cylindrical eminence passing in an external direction from 
 it. It is called the external geniculate body and receives, together 
 with the superior corpora quadrigemina, a large number of the 
 fibers of the optic nerve. A similar cylindrical eminence passes 
 outward from the inferior corpora quadrigemina. It is called the 
 internal geniculate body, and receives with the inferior corpora 
 quadrigemina fibers from tracts originating in connection with the 
 nucleus of the auditory nerve, situated below the medulla. 
 
 The Third Ventricle At its upper extremity the iter of Syl- 
 vius enters the third ventricle. This is a narrow, cleft-like cavity, 
 contained between two large nuclei of gray matter called the optic 
 thalami. 
 
 The optic thalami form the most important and last subrelay 
 station for many tracts between the cerebrum and lower portions 
 of the brain or spinal cord. 
 
 The third ventricle is roofed in by the concave lower surface of 
 the corpus callosum, a large mass of nerve fibers which collected in 
 an elongated, flattened bundle connects the two cerebral hemi- 
 spheres. It is curved in such a manner to be convex above and 
 concave below. 
 
 The floor of the third ventricle is formed of the following 
 structures beginning at the front: The anterior perforated space, 
 a flat plane of gray matter which, with the infundibulum, forms a 
 funnel-like cavity, leading down to the stalk of the pituitary gland, 
 a pea-sized structure situated below and between the two. 
 
 Behind the infundibulum is another flattened plane, the tuber 
 cinereum. More posterior are two knob-like structures, one on each 
 
 186 
 
THE NERVOUS SYSTEM 
 
 side of the middle line, called the corpora mammillaria or corpora 
 albicans. 
 
 Between these and the anterior opening of the Sylvian aque- 
 
 Fig. 79. Under-surface of a simply convoluted European brain. (Quain.) 
 Sulci orb., orbital (sagittal rami) ; o. tr., transverse orbital; olj., olfactory; 
 ti, tz, tz, first, second, and third temporal; coll., collateral (fourth temporal); 
 cole., calcarine. 
 
 Gyri R, gyrus rectus; T lf T s , T*, T 5 , first, third, fourth, and fifth tem- 
 poral; H, hippocampal; s.r.a., caput gyri hippocampi; unc., uncus. 
 
 ch., chiasma; s.p.a., substantia perforata antica; i.e., tuber cinereum; m, 
 corpora mammillaria, accidentally separated from one another in the prepara- 
 tion; cr., crusta; tm, tegmentum; spl. f splenium of callosum. 
 
 duct, or iter of Sylvius, is another inclined, flattened plane of gray 
 matter, the posterior perforated space. Immediately above the an- 
 terior opening of the iter of Sylvius is the posterior commissure, 
 consisting of a band of white fibers running across the two sides of 
 
 188 
 
THE NERVOUS SYSTEM 
 
 the brain in this situation and composed of commissural fibers con- 
 necting the posterior termination of the visual tracts. The extrem- 
 ities of the commissure are in close relation to the superior corpora 
 quadrigemina. 
 
 Above this commissure are the two stalks of the pineal gland, 
 which rests upon a flattened triangular surface in front of and 
 
 Genu of corpus callosum. 
 Cingulate 
 
 Body of corpus callosu 
 Intermediate mass. 
 Fornix. 1 I 
 Septum pellucidum. 
 Marginal gyrus., JUJ-Jgssj 
 
 fissure 
 
 Tela choroklea ventriculi tertll. 
 Cingulate gyrus. 
 Callosal fissure. 
 
 Splenium of corpus callosum. 
 Paraeentral lobule. 
 <VntraI tissure. 
 
 Subparletal fissure. 
 Precuneate lobnlo 
 ii- 
 
 tissure. 
 Calcarine 
 fissure. 
 Cuneate 
 lobule 
 
 Lamina terminalis. 
 
 Optic recess. 
 
 Optic nerve. 
 
 Optic commissure. 
 
 Hypophysis. 
 
 Anterior commissure. 
 Foramen of Monro. 
 
 Third nerve. 
 Corpus mammillare. 
 Third ventricle. 
 Cerebral peduncle. 
 Pons. 
 Suprapineal recess. 
 
 Pineal body. 
 Cerebral aqueduct. 
 
 Cerebellum. 
 Medulla oblongata. 
 Fourth ventricle. 
 Superior medullary velum. 
 Corpora quadrigemina. 
 
 Fig. 80. Median section of an adult brain. (Quain.) 
 
 between the two superior corpora quadrigemina. This surface is 
 called the trigonum habenulce. 
 
 Two other commissures cross the, third ventricle, the middle and 
 anterior commissure. The former connects the two optic thalami, 
 and the latter is situated at the extreme anterior end of the third 
 ventricle at the upper extremity of the anterior perforated space, 
 and is in relation with it. It contains commissural fibers of the 
 olfactory system. One more bilateral band of commissural fibers, 
 the pillars of the fornix and the fornix itself, appears in the third 
 
 190 
 
THE NERVOUS SYSTEM 
 
 ventricle. They run in an anteroposterior direction. They emerge 
 from the corpora albicans, run forward to curve in front of the 
 foramen of Monro, and then, reaching the roof of the third ven- 
 tricle, they run backwards upon the under surface of the corpus 
 callosum, diverging as they pass backwards so that ultimately they 
 acquire a position a little external to the third ventricle, appearing 
 by their external edge in the cavity of the lateral ventricle upon 
 the upper and posterior surface of the optic thalami. In this situa- 
 tion on the side of the lateral ventricle they are overlapped by a 
 vascular fold of the ependyma or remnants of the layer of epithe- 
 lium which originally forms the roof of the third ventricle, before 
 the latter with its ependymal roof is covered over by the back- 
 wardly growing hemispheres. The ependyma in this manner be- 
 comes enclosed between the fore- and mid-brain and to some extent 
 inverted laterally into the cavity of the lateral ventricle by its rich 
 supply of blood vessels. It is appropriately named in this situation 
 the velum inter positum. 
 
 THE CEREBRAL HEMISPHERES 
 
 Their Development The cerebral hemispheres are formed by 
 an enormous growth, at first forwards then upwards and finally 
 backwards, of the anterior extremity of the anterior cerebral ves- 
 icles. The optic thalami develop from the thickenings of the lateral 
 walls of the anterior cerebral vesicle and, therefore, belong essen- 
 tially to the third ventricle. 
 
 The Lateral Ventricles Inasmuch, however, as the cerebral 
 hemispheres grow from the anterior end of the anterior cerebral 
 vesicle, preserving within them a continuation of the cavity of the 
 anterior cerebral vesicle, they may be appropriately viewed as rep- 
 resenting a pre-cerebral vesicle, developed in front of the anterior 
 cerebral vesicle. This so-called pre-cerebral vesicle is carried back 
 with the backwardly growing cerebral hemispheres, and is pre- 
 served in the adult brain as the lateral ventricles. 
 
 The Foramen of Monro As the lateral ventricle is carried 
 backward external to the third ventricle, its connection with the 
 third ventricle is placed laterally on each side in the anterior ex- 
 tremity of the third ventricle. The passage of connection is called 
 the foramen of Monro. 
 
 192 
 
THE NERVOUS SYSTEM 
 
 194 
 
THE NERVOUS SYSTEM 
 
 The Body The lateral ventricle of the brain possesses a body 
 and three horns. (Figs. 82 and 83.) 
 
 The body is roofed over by the corpus callosum. Its inner wall 
 is bounded by the fornix, overlapped from below by the edge of the 
 
 Fig. 82. View of the lateral ventricle from above. Natural size. (Quain.) 
 The preparation was made with the brain in situ (hardened). The skull 
 cap and membranes having been removed, the brain was sliced down to the 
 level of the corpus callosum. The left lateral ventricle was then opened by 
 cutting away its roof, and the island exposed by slicing away the opercula. 
 The drawing is made from a photograph. 
 
 /. R., insula Reilii (the line points to the middle of the three gyri breves); 
 s.c., sulcus centralis insulae; g.L, gyrus longus insulse; c.c., corpus callosum; 
 n.L., nerves of Lancisi; str. t., stria tecta; f.mi., forceps minor; /.ma., forceps 
 major; c. a v cqrnu anterius of ventricle; c.p., cornu posterius; c.i., entrance 
 to cornu inferius; /. M ., foramen Monroi; s.M., sulcus leading backwards 
 to the foramen Monroi; c.str., nucleus caudatus of corpus striatum; th.opt., 
 thalamus, anterior tubercle; pl.ch., plexus choroides; /., fornix; /', its column; 
 h. t posterior end of hippocampus; tri., trigonum ventriculi; calcar, calcar 
 
 196 
 
THE NERVOUS SYSTEM 
 
 velum interpositum, called here the ckoroid plexus, because of the 
 vascular folds present in its edge. Its floor, which curves upward 
 externally to meet the roof, is formed from within outward by the 
 
 Fig. 83. View from above and the side of the whole left lateral ventricle. 
 Natural size. (Quain.) 
 
 This is a further dissection of the preparation shown in Fig. 82. The 
 insula has been sliced away and the inferior cornu, c. i., exposed. Within 
 this are seen the following parts: fi., fimbria, continued from the fornix; h., 
 the hippocampus; coll., the eminentia collateralis. The other lettering as in 
 Fig. 82. 
 
 upper surface of the optic thalamus, the tcenia semicircularis, a 
 band of white fibers extending from the region of the septum luci- 
 dum in front backward and outwards along the external superior 
 border of the optic thalamus, between it and a large elongated 
 
 198 
 
THE NERVOUS SYSTEM 
 
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 202 
 
THE NERVOUS SYSTEM 
 
 nucleus of gray matter immediately external to it and called the 
 caudate nucleus. 
 
 The Caudate Nucleus The caudate nucleus is a mass of gray 
 matter which really develops in the external, downwardly curving 
 fibers of the corpus callosum. It follows, therefore, the general 
 shape of the curve of the concave lower surface of this body and, 
 as well, the curve of optic thalami, from the outer border of which 
 it lies separated by the taenia semicircularis. 
 
 From within outwards the optic thalami, the taenia semicircu- 
 laris, and caudate nucleus form the floor of the body of the lateral 
 ventricle and the roof of its inferior horns. 
 
 The Anterior Horns The anterior horns of the two lateral 
 ventricles of the brain, arching around the anterior extremity of 
 the optic thalami, are separated from each other by the septum 
 lucidum, which contains the fifth ventricle. 
 
 The Posterior and Inferior Horns Only the space common to 
 both the inferior and posterior horns bounds the posterior extrem- 
 ity of the optic thalami. The floor of this common region is formed 
 by a rather large, discoid eminence called the trigonum ventriculi. 
 Beginning at an area anterior to this eminence and therefore be- 
 tween it and the posterior extremity of the optic thalamus and 
 extending to the tip of the inferior horn along its inner wall, is an 
 elongated, rounded eminence called the hippocampus major. It 
 ends anteriorly in a club-like extremity resembling an animal's 
 paw. Behind the posterior internal aspect of the trigonum ven- 
 triculi and, therefore, forming the internal wall of the posterior 
 horn, is another elongated, rounded eminence, the hippocampus 
 minor. Another elongated fold or ridge appearing in the inner 
 wall of the posterior horn is the calcar avis. It corresponds to an 
 important fissure on the internal surface of the brain. Above it in 
 the angle of the inner wall and roof of the posterior horn is a fold 
 caused by the fibers of the corpus callosum, running to the occipital 
 lobe of the brain. It is called the forceps major. 
 
 The Hemispheres The external surface of the brain presents 
 certain important fissures separating convolutions identified with 
 various nervous activities. 
 
 The Sylvian Fissure Upon the external surface is the Sylvian 
 fissure. A deep fissure running horizontally backwards from a 
 position corresponding to the posterior border of the lesser wing of 
 
 204 
 
THE NERVOUS SYSTEM 
 
 206 
 

THE NERVOUS SYSTEM 
 
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THE NERVOUS SYSTEM 
 
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 214 
 
THE NERVOUS SYSTEM 
 
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THE NERVOUS SYSTEM 
 
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THE NERVOUS SYSTEM 
 
 Great longitudinal fissure of the cerebrum Fissure 
 longitudinalis cerebri. 
 
 Frontal pole Polus frontalis 
 
 Olfactory sulcus Sulcus olfactorius. \ 
 Orbital sulcl Sulci orbitales. 
 
 Orbital gyri 
 
 Temporal pole Polus 
 temporalis. 
 
 Trigonum olfactorlum. -v 
 
 Optic commissure 
 or chiasma 
 Gbiasma opticum. 
 
 Uncus or hook of 
 the hippocampal 
 gyrus. 
 
 Entrance to the 
 choroidal fissure. 
 
 Collateral fissure 
 Fissura col- 
 lateralis. 
 
 Third (or Inferior) 
 temporal sulcus 
 Sulcus tempora'lis 
 inferior. 
 
 Third temporal gyrus 
 Isthmus of the gyrus \ 
 nicatus Isthmus gyri 
 fornicata. 
 
 Olfactory bulb Bulbus olfactorius. 
 
 Olfactory tract Tractus olfactorius. 
 
 Gyrus rectus, or straight gyrus. 
 
 Root of the olfactory tract, inner 
 or mesial, middle or gray and 
 outer or lateral root Striae 
 olfactoriae, medialis, inter- 
 media lateralis. 
 Anterior perforated space 
 Substantia perforata 
 anterior. 
 
 x Limen Insulse, or thresh- 
 old of the island. 
 Fissure of Sylvius 
 Fissura cerebri lat- 
 eralis (Sylvii). 
 
 Nucleus amygdalae, 
 or amygdaloid nu- 
 cleus. 
 
 Cerebral peduncle or 
 crus cerebri 
 (crusta) Pedun- 
 culus cerebri 
 (based pedunculi). 
 
 Posterior perforated 
 space or fossa of 
 Tarini Substantia 
 perforate posterior. 
 
 Substantia nigra. 
 
 Tegmentum. 
 
 3/4 
 
 Fourth temporal gyrus. 
 
 Aqueduct of Sylvius 
 
 Aqueeductus cerebri (Sylvii). 
 Quadrigeminal lamina Lamina 
 quadrigemina. 
 
 Splenium of the corpus callosum Splenium 
 
 Gyrus fornicatus Gyrus fornicatus. j i corporis callosi. 
 
 Occipital pole Pole occipitalis. Fifth temporal gyrus. Hippocampal gyrus. 
 
 Great longitudinal fissure of the cerebrum Fissure longitudinalis cerebri. 
 
 Fig. 94. The inferior or basal surface of the cerebrum, facies basalis cerebri; the whc 
 extent of this surface is visible, the medulla oblongata, pons varolii, and cerebellum 
 (i.e., the rhombencephalon) having been removed by a transverse section through the 1 
 mid-brain. Convolutions and furrows of the hemispheres, gyri et sulci cerebri. The 
 frontal, temporal, and occipital poles of the hemispheres. 
 
 The anterior extremity of the left temporal lobe has been cut away, the optic com- 1 
 missure or chiasma has been cut through in the median plane, and its left half has been . 
 removed. The anterior perforated space has thus been fully exposed on the left side, 
 and its relations to -the threshold of the island, limen insulse, and to the parts of the 
 rhinencephalon situate on the mesial surface of the hemisphere, have been made mani- I 
 fest. The olfactory tract, tractus olfactorius, has been cut away on the right side, in order 
 to display the olfactory sulcus. (Toldt.) 
 
 222 
 
THE NERVOUS SYSTEM 
 
 the sphenoid to terminate in a posterior, upturned extremity in the 
 center of the parietal lobe. It separates the frontal lobes and an- 
 terior portion of the parietal lobes from the temporal lobes. 
 
 The Fissure of Rolando The Fissure of Rolando, beginning 
 at a point corresponding on the external surface of the skull to .55 
 of the distance from the frontal prominence to the occipital tuber- 
 cle, it runs downwards and forwards at an angle of 67% until it 
 nearly reaches the fissure of Sylvius. It separates the frontal from 
 the parietal lobes. 
 
 Superior and Inferior Precentral and Intraparietal Fissures 
 Fissures parallel to the fissure of Eolando, the superior and inferior 
 precentral fissures in front, and the intraparietal fissure behind, 
 separate the ascending frontal convolution from the rest of the 
 frontal lobe and the ascending parietal convolution from the rest 
 of the parietal lobe. The remainder of the external surface of the 
 frontal lobe is composed of the superior middle and inferior, or 
 first, second and third frontal convolutions. 
 
 Parietal Lobes The remainder of the parietal lobe is com- 
 posed of the superior parietal lobe, contained between the forks of 
 the upper extremity of the intraparietal fissure; the supra-marginal 
 convolution, curving around the posterior upper extremity of the 
 fissure of Sylvius, and the angular convolution which curves around 
 the posterior extremity of the superior temporal fissure. 
 
 Superior Temporal Fissure The superior temporal fissure 
 runs below and parallel to the fissure of Sylvius and separates the 
 first or superior temporal convolution from the second or middle 
 temporal convolution. 
 
 The Boundaries of the Occipital Lobe Posterior to the parie- 
 tal and superior, middle and inferior temporal convolutions is the 
 occipital lobe. It is separated from these lobes on the external sur- 
 face of the hemisphere by an imaginary line drawn from the point 
 where the occipito-parietal fissure appears on the external surface 
 of the brain and the pre-occipital notch. The last is an indentation 
 on the brain produced by the attachment of the anterior border of 
 the tentorium cerebelli. The frontal, parietal, occipital and tem- 
 poral lobes extend over upon the internal surface of the brain. 
 
 The Calloso-marginal Fissure The inferior limit of the fron- 
 tal lobe on the internal surface of the hemisphere is founded by the 
 c all o so -marginal fissure. This fissure is a prominent fissure run- 
 
 224 
 
THE NERVOUS SYSTEM 
 
 ning concentric with the corpus callosum about half way between 
 the latter and the free margin of the internal surface of the hemi- 
 sphere. Its posterior extremity turns upward to the free margin 
 of the internal surface of the hemisphere in the parietal lobe to a 
 point posterior to the fissure of Rolando. 
 
 The Limbic Lobe The calloso-marginal fissure separates the 
 frontal lobe from the falciform or cingulate or limbic lobe. All of 
 
 S. precentralls meslalis 
 
 S. centralis (Roland!) . 
 Pars marginalis s 
 
 cinguli. 
 
 S. parietalis 
 
 superior 
 
 S. parieto- 
 occipitalis. 
 
 S. cinguli. 
 
 S. corporis callosi. 
 
 __ rostralis. 
 
 Incisura temporalis. 
 
 calcarinus. 
 
 S. subparietalis. 
 
 S. collaterals. 
 
 Fascia dentata. 
 
 collateralis. 
 temporalis inferior. 
 
 Fig. 95. Left cerebral hemisphere from the mesial aspect. Natural size. 
 
 (Quain.) 
 
 The label "caput hippocampi" has been placed too far forwards. The caput 
 hippocampi does not extend in front of the incisura temporalis. 
 
 these names are given to the convolutions below the calloso-mar- 
 ginal fissure. They are concentric with the corpus callosum and 
 curve around its anterior and posterior extremity. Below the pos- 
 terior extremity of the corpus callosum it becomes connected by a 
 narrow constricted portion with an anterior second enlarged por- 
 tion. This enlarged portion ends anteriorly in the uncus, which is 
 the anterior extremity of the limbic lobe, marked oft 3 by a narrow 
 fissure, the dentate fissure, from the rest of the limbic lobe. 
 
 The Precuneus Between the posterior upturned end of the 
 
 226 
 
THE NERVOUS SYSTEM 
 
 calloso- marginal fissure and another fissure, the subparietal fissure, 
 which continues the general curve of the calloso-marginal fissure 
 around corpus callosum, is the portion of the parietal lobe which 
 appears on the internal surface of the hemispheres. This portion of 
 the parietal lobe is called the precuneus. That portion of the 
 parietal lobe appearing on the internal surface of the hemispheres 
 in front of the precuneus is called the lobulus quadratus. 
 
 The Occipital Parietal Fissure Behind the precuneus is the 
 occipital parietal fissure, which separates the precuneus from the 
 occipital lobe. 
 
 Calcarine Fissure The occipital lobe is divided into two parts 
 by a deep fissure, curving downwards and backwards from the mid- 
 dle of the occipital parietal fissure toward the posterior pole of the 
 brain. This fissure is called the calcarine fissure. 
 
 Above the calcarine fissure the occipital lobe is called the cuneus 
 and below but more anteriorly the lobulus lingualis. 
 
 Collateral Fissure Beneath the lobulus lingualis, separating 
 it and, more anteriorly, the limbic lobe from the portion of the tem- 
 poral lobe which appears on the internal surface of the hemisphere, 
 is the collateral fissure. It runs horizontally between the lobes 
 which it separates. The dentate fissure, a small fissure in the limbic 
 lobe above and parallel to the collateral fissure produces the promi- 
 nence of the hippocampus major upon the inner wall of the inferior 
 cornu of the lateral ventricle. The calcarine fissure produces the 
 eminence of the calcar avis on the inner wall of the posterior cornu 
 of the lateral ventricle. 
 
 The Fornix The bundle of fibers forming the f ornix terminate 
 posteriorly in hippocampus major and eminentia collateralis 
 structures to be mentioned later, and appearing in the floor of the 
 descending horn of the lateral ventricle and posterior to the optic 
 thalamus. They are continued through the synapses of the corpora 
 albicans as another bundle, the bundle of Vicq d 'Azyr, which curves 
 directly out of the corpora albicans into the optic thalami. 
 (Fig. 96.) 
 
 The Character of the Cortex The external walls bounding the 
 lateral ventricles as a whole, i.e., the later transformation of the 
 precerebral vesicle, become very much thickened in all aspects 
 except the internal, in other words, above, externally, below, in 
 
 228 
 
THE NERVOUS SYSTEM 
 
 230 
 
 
THE NERVOUS SYSTEM 
 
 front and behind. This thickening, thrown into folds on its outer 
 surface, constitutes the cortex and white matter of the cerebrum. 
 
 The Fifth Ventricle In front of the foramen of Monro the 
 brain cortex becomes coapted and united in such manner that it 
 incloses a hollow cavity, which therefore at no time was a part of 
 the system of original cerebral vesicles. 
 
 This cavity is called the fifth ventricle of the brain. Its walls, 
 which are formed of thin layers of gray matter, are called the sep- 
 tum lucidum. 
 
 The Relation of the Optic Thalami to the Lateral Ventricles 
 The primarily posterior and later internal walls of the lateral ven- 
 tricle inclose the optic thalamus of the corresponding side by 
 curving around the latter. The anterior horn curves around the 
 anterior rounded end of the optic thalamus and the inferior horn 
 curves around the posterior extremity of the optic thalamus and 
 so completely that at the origin of this horn its floor is formed by 
 the optic thalamus, while at its extremity its roof is formed of the 
 optic thalamus. 
 
 The posterior horn curves around in an external direction the 
 posterior extremity of the optic thalamus largely in the same hori- 
 zontal plane as that of the body of the lateral ventricle. 
 
 THE INTERNAL STRUCTURE OF THE BRAIN 
 
 There are two important differences between the internal struc- 
 ture of the cord and that of the medulla, which represent changes 
 of development undergone by the medulla from the manner in 
 which the cord develops. 
 
 The first of these is the displacement of the central canal pos- 
 teriorly until it no longer forms a canal but a median groove upon 
 the floor of the fourth ventricle. The second change is the cutting 
 up of the gray matter of the anterior horns by fibers of the pyram- 
 idal tracts crossing the middle line arid decussating with each other 
 until, practically entirely crossed, they occupy a situation on each 
 side of the middle line producing two rounded eminences upon the 
 anterior surface of the lower half of the medulla, immediately be- 
 neath the pons. 
 
 As the central canal of the spinal column opens up into the 
 medulla, the gray matter of the posterior horns becomes displaced 
 
 232 
 
THE NERVOUS SYSTEM 
 
 laterally and the gray matter, now in part interspersed between the 
 fibers of the crossing pyramidal tracts, also becomes displaced to a 
 position on each side of the middle line in the floor of the fourth 
 ventricle. Hence it is that the sensory nuclei of the cranial nerves 
 always occupy a more lateral position than the motor nuclei. The 
 cranial nerves may be divided into motor nerves and sensory nerves. 
 A number of them have both sensory and motor roots. 
 
 Fig. 97. Diagrams illustrating the origin and relations of the root-fibres of 
 
 the cerebral nerves. (Quain.) 
 
 A, efferent fibres only; lateral view. B shows on the left the motor nuclei 
 and efferent fibres, except those of the fourth nerve, and on the right side 
 the afferent fibres; surface view. 
 
 The Nuclei and Superficial Origin of the Motor Cranial Nerves 
 
 (Figs. 97-100) From below upwards the motor nerves are the 
 twelfth, the seventh, the motor portion of the sixth, the fifth, the 
 fourth and the third. The nuclei of the twelfth and sixth nerves lie 
 in the gray matter of the floor of the fourth ventricle, close to the 
 middle line, one below and the other above the striae acusticae in just 
 the position which the displaced gray matter, corresponding to the 
 anterior horns of the spinal column, should occupy as the conse- 
 
 234 
 
THE NERVOUS SYSTEM 
 
 quence of the opening out process of the central canal of the spinal 
 column. The nerve fibers arising from the cells of these become 
 collected in bundles which pass outwards and forwards to emerge in 
 a series of roots in the groove between the pyramids and the olivary 
 body. 
 
 In the same manner the sixth nerve emerges from the medulla at 
 the lower border of the pons at the upper end of the same groove. 
 
 In direct line with these nuclei, close to the iter of Sylvius, is the 
 
 Nucleus of tractus solitarius. 
 
 Nucleus of ala cinerea. i Medial nucleus and descending root of 
 
 vestihular nerve. 
 
 Nucleus of fasciculus cuneatus. 
 
 s Nucleus ambiguus. 
 -. Restiforra body. 
 
 Root filum of vagus cerebello- 
 olivary fibres. 
 
 Ventral external arcuate fibres 
 
 Fig. 98. Diagram showing tEe composition of the jerebellar portions of the 
 internal and external arcuate fibres. (Morris.) 
 
 column of nerve cells forming the nuclei of the fourth and third 
 nerves. The fibers of the fourth nerve become collected into a 
 bundle which passes backwards along the outer side of the nucleus 
 until they reach the upper limits of the medulla where they decus- 
 sate and, after the crossing, emerge on each side from the groove 
 at the lower margin of the inferior corpora quadrigemina, between 
 this latter and the superior peduncle of the cerebellum. The other 
 cranial nerves possess motor and sensory roots, but the nuclei of 
 the motor roots always lie internal to those of the sensory roots. 
 Thus it is that nucleus of the vagus or tenth nerve, which is partly 
 motor and partly sensory, lies under the ala cinerea external to the 
 position of the origin of the twelfth nerve. The motor portion of 
 the tenth arises from a separate nucleus, the nucleus anibiguus, 
 
 236 
 
THE NERVOUS SYSTEM 
 
 :/ Nucleus of olfactory nerve. 
 
 Nucleus of oculomotor nerve. 
 Nucleus of trochlear nerve 
 Nucleus of mesencephalic 
 
 root of masticator. 
 Chief motor nucleus of 
 masticator. 
 
 Nucleus of facial. 
 
 Nucleus of abducens.- 
 
 Nucleus ambiguus (vagus, 
 
 and glossopharyngeus). 
 
 Nucleus of hypoglossus 
 
 Nucleus of spinal accessory nerve. . - 
 
 \ Pulvinar of thalamus. 
 
 Lateral geniculate body. 
 Nucleus of superior colliculus, 
 
 or corpus quadrigeminum. 
 -\" Sensory nucleus of trigeminus. 
 Nucleus of vestlbular nerve. 
 
 Ventral nucleus of 
 cochlear nerve. 
 
 - - ' Dorsal nucleus of cochlear nerve. 
 
 Nucleus alse cinereae (vagus and 
 glossopharyiigeus) . 
 
 Solitary tract (vagus and 
 ?J/"~~ glossopharyngeus). 
 
 -Nucleus of spinal tract of trigeminus. 
 
 Fig. 99. Scheme showing the relative size and position of the nuclei of 
 
 origin of the motor and the nuclei of termination 
 
 of the sensory cranial nerves. (Morris.) 
 
 238 
 
THE NERVOUS SYSTEM 
 
 Insula. 
 
 Anterior perforated 
 substance. 
 
 Mammillary bodies. 
 
 Cerebral peduncle 
 
 Semilunar (Gasserian) 
 
 ganglion. 
 
 Oblique fasciculus of 
 pons. 
 
 Olfactory tract. 
 
 i Hypophysis. 
 
 Optic nerve. 
 Optic tract. 
 
 Tuber cinereum. 
 
 Oculomotor 
 
 nerve (III), j 
 
 _ Lateral genicu- j 
 
 late body. 
 Trochlear nerve 
 - (IV). 
 
 Masticator .nerve 
 (motor root oft 
 trigeminus). ) 
 """^Trigeminus (V).J 
 
 Abducens (VI). 
 
 Hypoglossal nerve (XII). 
 
 Brachium of 
 
 Pons. 
 Facial nerve 
 
 (VII). 
 . Glosso-palatine 
 
 (intermediate pai 
 of facial). 
 Cochlear and v 
 
 tibular n e r v e sjj 
 \ (acoustic or VIII). j 
 
 Glossopharyngeal 
 nerve (IX). 
 
 Vagus nerve (X). 
 
 Accessory nerve (XI) 
 (spinal accessory). 
 
 v Cervical I. 
 
 Cervical II. 
 
 Pyramid. 
 Decussation of pyramids. 
 
 Fig. 100. Semi-diagrammatic representation of the ventral aspect of the rhombencephah 
 and adjacent portions of the cerebrum. (Morris.) 
 
 240 
 
THE NERVOUS SYSTEM 
 
 which lies internal to the sagittal plane of the main nucleus. The 
 fibers of the third nerve pass directly outward and ventral-wards, 
 traversing the substance of the mid-brain to emerge close to the 
 middle line on the ventral surface of the mid-brain between the 
 diverging crura cerebri. 
 
 The seventh nerve arises from a nucleus external and ventral to 
 and slightly below the nucleus of origin of the sixth nerve, deeply 
 placed beneath the floor of the upper half of the fourth ventricle. 
 Its nucleus would seem at first sight to be too far laterally placed 
 for a motor nucleus, but its deeper position in the recticular forma- 
 tion explains this apparent irregularity, for it must be remembered 
 that all the motor nuclei of the cranial nerves occupied originally 
 the position of the laterally placed anterior horns and in the open- 
 ing out process of the central canal of the spinal column they are 
 at first displaced from a lateral position to an internal one. The 
 seventh nerve possesses also a sensory root, which maintains its 
 integrity as a separate bundle of fibers at the superficial origin of 
 the nerve. Its incoming fibers, like other sensory nerves, divide into 
 ascending and descending fibers which terminate around cells con- 
 tinuing the column of the ninth nerve further upwards. The fibers 
 of the main portion of the seventh nerve are motor and become col- 
 lected into a bundle which forms a peculiar curve, at first down- 
 wards and inwards and backwards, then directly upwards and then 
 downwards and outwards and forwards in a manner to completely 
 encircle the nucleus of the sixth nerve. It finally emerges in the 
 groove between the pons and the medulla just anterior to the posi- 
 tion of the superficial origin of the eighth nerve. 
 
 The Sensory Nuclei It must of course be remembered that 
 the nuclei of the sensory nerves are not to be viewed as nuclei of 
 origin, as is the case with the nuclei of the motor nerves. 
 
 The* nuclei of the sensory nerves are collections of nerve cells 
 around which the termination of the sensory fibers arborize. 
 Though more deeply placed, the nucleus of the ninth nerve simply 
 continues upwards, the column of cells of origin of the vagus 
 underlying, in the floor of the fourth ventricle, an area beginning 
 in the gray matter of the ala cinereum and extending upwards 
 external to the trigonum hypoglossi to nearly the level of the striae 
 acusticae. 
 
 The fifth nerve possesses a separate motor and sensory portion. 
 
 242 
 
THE NERVOUS SYSTEM 
 
 The position of its nuclei follows the general rule of the other 
 cranial nerves. The motor nucleus is situated at a little depth 
 below the uppermost portions of the pontine part of the medulla, 
 at its extreme lateral portion. 
 
 This, however, is not a very great distance from the middle 
 line, inasmuch as the fourth ventricle is quite narrow at this level. 
 The column of cells of the main portion of the motor nucleus is 
 continued brainwards, forming a streak of gray matter external 
 and ventral to the nuclei of the fourth and third nerve from 
 which fibers run downwards forming one bundle with the fibers of 
 the main motor nucleus. The collected fibers of the motor portion 
 of the fifth nerve emerge from the lateral surface of the pons. 
 
 The incoming fibers of the sensory portion of the fifth nerve 
 enter the pons immediately below the motor root. They traverse 
 the substance of the pons and divide into ascending and descend- 
 ing bundles. The ascending bundles pursue a shorter course and 
 terminate around cells forming a nucleus which lies near the 
 lateral margin of the pons, lateral to the motor nucleus, though 
 not extending iriuch above the level of the upper limits of the 
 fourth ventricle. 
 
 The descending fibers run downwards for a very long distance, 
 no less than as far as the level of the second cervical nerve. This 
 descending root occupies a position at first in the lateral boun- 
 daries of the pons in the substance of the transversely running 
 fibers of this structure. In lower levels it lies close to the super- 
 ficial lateral surface of the medulla internal and posterior to the 
 corpus restiforme and crossed laterally by the fibers of the eighth 
 nerve. Still lower it forms a cap at the tubercle of Rolando and 
 the substantia gelatinosa of Rolando, and may be traced as far 
 down as the second cervical vertebrae. Most of its fibers terminate 
 in the chief sensory nucleus, situated dorsally to it in the upper 
 level of the pons, lateral and ventral to the position of the motor 
 nucleus, coming very close to the lateral surface in an area indi- 
 cated by the angle formed by the superior and middle peduncles 
 of the cerebellum. 
 
 The Eighth Cranial Nerve The only remaining cranial nerve, 
 exclusive of the optic and olfactory tracts, which are not peripheral 
 nerves at all but bundles of nerve fibers comparable to intra- 
 cerebral tracts, is the eighth cranial nerve. It is proper to consider 
 
 244 
 
 
THE NERVOUS SYSTEM 
 
 this nerve in a class by itself or with the optic and olfactory nerves 
 as it is so specially proprioceptive in its character that it stands 
 quite apart from the other cranial nerves. 
 
 The eighth cranial nerve is composed of two portions, entirely 
 different in function. Both arise in the sensory cells of the in- 
 ternal ear. One hundle of fibers constitutes the auditory division 
 of the nerve and the other the vestibular division. Both divisions, 
 
 n.XE 
 
 Fig. 101. Transverse section at the upper part of the medulla oblongata. 
 
 (Quain.) 
 
 Py, pyramid; o, olivary nucleus; d. V., descending root of the fifth nerve; 
 VIII, root of the acoustic nerve, formed of two parts, a (cochlear) and b 
 (vestibular), which enclose the restiform body, c. r.; n.VIIIp, dorsal nucleus 
 of the vestibular nerve; n. VIII ac, ventral acoustic nucleus; g, ganglion-cells, 
 of the acoustic tubercle (lateral acoustic nucleus); n.f.t., nucleus of the 
 funiculus teres; n.XII, nucleus of the hypoglossal; r, raphe. 
 
 however, enter the medulla just beneath the pons Varolii as one 
 nerve, parted as they enter the medulla into a dorsal and ventral 
 division which inclose between them the restiform body. (Fig. 
 101.) However, it is only the auditory fibers which divide to in- 
 close the restiform body. All of the vestibular fibers pass meso- 
 ventral to this structure. After it has entered the medulla the ves- 
 tibular division divides, like other sensory nerves, into an ascending 
 and descending portion. Both divisions pass to the cells underlying 
 
 246 
 
THE NERVOUS SYSTEM 
 
 the area in the floor of the fourth ventricle, termed the trigonum 
 acusticum. 
 
 The ascending division passes to the upper portion and the 
 descending division to the lower portion. From these fibers col- 
 laterals join two other important nuclei the nuclei of Bechterew 
 and Deiters, placed internal and ventral to the restiform body. 
 Many fibers of the vestibular nerve end directly around the cells 
 of these nuclei. The fibers of the auditory division of the eighth 
 
 tub.ac. 
 
 FIBRES TO NUCL.LEMNISCI 
 &CORPORA QUADRIGEMINA 
 
 NERVE-ENDINGS 
 
 IN ORGAN OF CORTI 
 
 Fig. 102. Plan of the course of connections of the fibres forming the cochlear 
 
 root of the auditory nerve. (Quain.) 
 
 r., restiform body; V, descending root of the fifth nerve; tub.ac., tuber- 
 culum acusticum ; n. ace., accessory nucleus ; s. o., superior olive ; n. tr., nucleus 
 of trapezium ; n. VI, nucleus of sixth nerve ; VI, issuing root-fibre of sixth 
 nerve. 
 
 nerve divide to inclose the restiform body. The dorso-lateral 
 fibers end around cells forming a prominence, the tuberculum acus- 
 ticum, on the posterior surface of the restiform body, just above 
 the trigonum acusticum and in many cells interspersed among the 
 fibers of the dorsal division itself. The striae acusticae themselves 
 are composed of fibers originating as the axis cylinders of these 
 nerve cells. They pass internally, crossing the middle line and, 
 therefore, the fibers of the opposite side. As soon as they have 
 crossed to the opposite side they dip down close to the middle 
 line to enter the deep portions of the medulla to be continued to 
 
 248 
 
THE NERVOUS SYSTEM 
 
 the inferior corpora quadrigemina in a manner to be subsequently 
 described. (Fig. 102.) 
 
 The fibers of the auditory nerve, which pass meso-ventrally to 
 the corpus restiforme, end around cells to the inner and ventral 
 side of this body, for the most part placed between the auditory 
 and vestibular divisions of the eighth nerve. Higher up these 
 cells become continuous with the nuclei of the meso-ventral divi- 
 sion. From these nuclei fibers also arise which cross the middle 
 
 TO VERMIS 
 
 TO HEMISPHERE 
 
 FIBRES OF 
 
 VESTIBULAR 
 
 ROOT 
 
 NERVE 
 ENDINGS 
 IN MACULXE 
 &AMPULL/E 
 
 Fig. 103. Plan of the course and connections of the fibres forming the ves- 
 tibular root of the auditory nerve. (Quain.) 
 
 r., restiform body; V, descending root of fifth nerve; p., principal nucleus 
 of vestibular root ; d, fibres of descending vestibular root ; n. d., a cell of the 
 descending vestibular nucleus; D, nucleus of Deiters; B, nucleus of Bech- 
 terew; n. t., nucleus tecti (fastigii) of the cerebellum; plb., posterior (dorsal) 
 longitudinal bundle. 
 
 line, deeply decussating in the medulla in a manner to be later 
 described and ultimately reach the inferior corpus quadrigeminum 
 of the opposite side. (Figs. 102 and 103.) 
 
 We have now considered the change produced in the medulla 
 by the opening out pf the central spinal canal, and the effect which 
 this change has produced upon the location of the nuclei of the 
 cranial nerves. 
 
 The Nuclei Cuneatus and Gracilis It now remains to con- 
 
 250 
 
THE NERVOUS SYSTEM 
 
 sider the new nuclei appearing throughout the medulla and mid- 
 brain and the further course through the medulla and mid-brain 
 of the axis cylinders of these nuclei, of the nuclei of the afferent 
 cranial nerves and of other great sensory tracts. The first impor- 
 tant new masses of gray matter met with are the nuclei cuneatus 
 and gracilis, at the level of the lower half of the medulla oblongata 
 
 Funiculus gracilis 
 Dorsal median fissure. 
 
 Funiculus cuneatus. 
 Nucleus gracilis. 
 
 Descending root of Vth. 
 Bundle from funiculus 
 cuneatus. 
 Substantia Rolandl. 
 
 Bundle of Flechsig. 
 Pyramid-tract bundles. 
 
 Decussation of pyramids. 
 
 Caput cornu ventralis. 
 
 Ventral median fissure. 
 
 Pyramid. 
 
 Fig. 104. Section across the lower part of the medulla oblongata in the 
 
 middle of the decussation of the pyramids. Magnified 
 
 about six diameters. (Quain.) 
 
 situated on its dorso-external aspect, external to the fourth 
 ventricle. They receive around their nerve cells the terminal 
 arborizations of the fibers of the posterior columns of Goll and 
 Burdach respectively. (Figs. 104 to 107.) 
 
 Tubercle of Rolando Another nucleus of gray matter ex- 
 ternal and ventral to the nucleus cuneatus is the tubercle of 
 Rolando. This is not a new mass of gray matter but it will 
 make the description clearer to mention it at this place. The 
 tubercle of Rolando is merely the enlarged upper extremity of the 
 gray substance of the substantia gelatinosa of Rolando around 
 
 252 
 
THE NERVOUS SYSTEM 
 
 the posterior horns. Around its cells doubtlessly terminate many 
 fibers of the descending root of the fifth nerve. 
 
 Corpus Restiforme (Figs. 109-111) The tubercle of Ro- 
 lando appears to be overlapped at its upper extremity by bundles 
 of fibers (two bundles in particular) which join to form the begin- 
 ning of the inferior peduncle of the cerebellum and constitute the 
 corpus restiforme. This body, therefore, is in the lateral aspect 
 
 Ftmiculus gracilis. 
 Funiculus cuneatus. 
 
 Funiculus Rolandi. 
 Substantia Rolandi. 
 
 Bundle of Flechsig. 
 Lateral nucleus. 
 
 Caput cornu ventralis. 
 
 Dorsal median fissure. 
 
 Nucleus gracilis. 
 Nucleus cuneatus. 
 
 Central canal. 
 
 Decussation of 
 pyramids. 
 
 Ventral median 
 fissure. 
 
 Pyramid 
 
 Fig. 105. Section across the medulla oblongata at the level of the upper- 
 most part of the decussation of the pyramids. (Quain.) 
 
 of the medulla, just below the pons Varolii and just above the 
 tubercle of Rolando and the termination of the column of Burdach 
 in the nucleus cuneatus. 
 
 Olivary Nucleus A third new mass of gray matter appear- 
 ing in the medulla is the olivary nucleus. It presents a wavy 
 appearance on cross section, arranged in a curved manner, concave 
 internally, and produces a very decided prominence between the 
 prominences of the pyramids and the tubercle of Rolando imme- 
 diately below the pons Varolii. 
 
 Superior Olive The fourth new mass of gray matter is the 
 
 254 
 
THE NERVOUS SYSTEM 
 
 superior olivary nucleus, smaller and situated above the main 
 olivary nucleus, in among the transversely coursing fibers of the 
 pons Varolii itself. 
 
 Formatio Reticularis The transversely running fibers of the 
 pons Varolii form a large portion of the pontine portion of the 
 
 Gracile nucleus 
 
 Fasciculus cuneatus 
 
 Cuneate nucleus. 
 
 Tractus solitarius. 
 Tractus spinalis of 
 
 trigeminal nerve. 
 Nucleus of tractus 
 
 spinalis of trigemi- 
 
 nal nerve. 
 Internal arcuate fibre. 
 
 Fila. of hypoglossal 
 nerve. 
 
 External arcuate fibres. 
 
 Inferior olivary 
 nucleus. 
 
 Medial accessory olivary 
 nucleus. 
 
 Pyramid. 
 
 Central canal. 
 Hypoglossal nucleu> 
 
 Fasciculus 
 
 longitudinal is 
 
 medialis. 
 Hypoglossal nerve. 
 
 Raphe. 
 
 Medial lemniscus. 
 
 External arcuate 
 fibres. 
 
 Fig. 106. Transverse section through the middle of the olivary region of 
 
 the human medulla oblongata. (Cunningham.) 
 
 The floor of the fourth ventricle is seen, and it will be noticed that the 
 restiform body on each side has now taken definite shape. 
 
 medulla. They are composed of a large number of interlacing 
 fibers passing between the two hemispheres of the cerebellum. 
 A portion of these fibers are the pyramidal tracts on their way 
 from the brain to the spinal cord. In other words, the fibers 
 of the pyramidal tracts plunge deeply into the pons Varolii and 
 become covered and broken up by the transverse fibers of this 
 structure before they become united again to form the pyramids 
 just above their decussatioi* Nevertheless, many of the pyram- 
 
 256 
 
THE NERVOUS SYSTEM 
 
 idal fibers remain collected in the pons in a fairly well-defined 
 bundle near the anterior surface of the pons. More dorsally 
 other transverse fibers, which at higher levels become longi- 
 tudinal, spring from the nuclei cuneatus and gracilis. Still other 
 transverse fibers cross the middle line from each olivary nucleus 
 and from each Deiters' nucleus. All these fibers, with others origi- 
 
 Pasciculus cuneatus. 
 Vestibular nucleus. 
 Restiform body. 
 Fasciculus solltarus. 
 
 Bundle of Flechsig. 
 
 Descending root of Vth. ~^E9 
 
 Substantia Rolandi. ~g||| 
 
 Part of descending 
 
 root of Vth. 
 Internal arcuate fibres. ... 
 
 Fibres of Xth 
 
 Bundle of Gowera. r 
 
 Raphe.- 
 Thalamo-olivary tract.- 
 
 Accessory olivary 
 nucleus. 
 Olivary nucleus. 
 
 Fibres of Xllth nerve. - 
 External arcuate fibres. 
 
 Pyramid. 
 Arcuate nucleus. 
 
 Dorsal 
 
 longitudinal 
 bundle. 
 
 Ventral 
 
 longitudinal 
 bundle. 
 
 Fig. 107. Section across medulla oblongata a little above the level of the 
 point of the calamus scriptorius. Magnified about six diameters. (Quain.) 
 
 nating from scattered cells among the fibers themselves, form a 
 confused network dorsal to the main mass of fibers of the pons 
 Varolii and constitute what is known as the 'formatio reticularis. 
 The Cerebellum The gray matter of the cerebellum, with 
 its contained nuclei, must also be considered as additional masses 
 of gray matter added to the primitive segmented cerebrospinal 
 axis of the invertebrates. As explained, it is connected by two 
 superior, two middle and two inferior peduncles, with respectively 
 the mid-brain, the medulla and the fourth ventricle. The cerebel- 
 
 258 
 
THE NERVOUS SYSTEM 
 
 260 
 
THE NERVOUS SYSTEM 
 
 262 
 
THE NERVOUS SYSTEM 
 
 I! 
 
 1 1 
 
 ! 
 
 I ,lt 
 
 ~ -So) : 
 
 8 5 ** q .S 
 
 a *-3 .SS 
 
 S 1 ^a 
 
 i 
 
 
 I! 
 
 i in 
 
 n; 
 
 o ^5 ^H fi-fi^ASdfi2:af>5 
 
 -5 cj'-Hej^cjOT1zia>-<^Q 
 
 : i Illilsl:i:ill 
 
 264 
 
THE NERVOUS SYSTEM 
 
 lum itself is composed of two lateral hemispheres and a central 
 lobe which latter appears as rounded eminences on the superior 
 and inferior surface of the cerebellum between the lateral hemi- 
 spheres. These eminences are termed the superior and inferior 
 
 Fig. 111. Transverse section of pons through the origin of the auditory nerve. 
 
 From a photograph. Magnified about four diameters. (Quain.) 
 v. IV, fourth ventricle; c., white matter of cerebellar hemisphere; c. d., 
 corpus dentatum cerebelli ; fl., flocculus ; c. r., corpus restiforme ; R, Roller's 
 "ascending" auditory bundle (really formed of descending fibres of vestibular 
 nerve); D, Deiters' nucleus; VIII, root of auditory nerve; VIII d., principal 
 nucleus of vestibular division; VIII v., ventral nucleus of cochlear nerve; 
 n. tr., small-celled nucleus traversed by fibres of the trapezium ; tr., trapezium ; 
 /., mam fillet; p.l.b., posterior or dorsal longitudinal bundle; j.r., formatio 
 reticularis ; n, n' , n" , nuclei in formatio reticularis ; V. a., so-called ascending 
 root of fifth (really descending); s. g., substantia gelatinosa; s. o., upper 
 olivary nucleus ; VII, issuing root of facial ; n. VII, nucleus of facial ; VI, 
 root-bundles of abducens; py., pyramid-bundles; n.p.> nuclei pontis. 
 
 vermis. (Figs. 120-122.) The entire surface of all lobes is com- 
 posed of gray matter, thrown into folds for the purpose of increas- 
 ing its surface. 
 
 Its Nuclei In the center of each lateral hemisphere is placed 
 
 266 
 
THE NERVOUS SYSTEM 
 
 Tractus 
 spinalis of 
 trigeminal 
 nerve. 
 
 Its nucleus. 
 
 Facial nerve. 
 
 Facial nucleus. 
 
 Superior olive. 
 
 Fasciculus v, ,\ 
 thalamo- 
 olivaris. 
 
 I.emniscus . 
 medialis. 
 
 Brachlum pontis. 
 
 Nucleus of 
 
 tractus. 
 Spinalis of 
 
 trigeminal 
 
 nerve. 
 Vestibular 
 
 nerve. 
 Tractus 
 
 spinalis of 
 
 trigeminal 
 
 nerve. 
 Facial nucleus. 
 
 Facial nerve. 
 Superior olive. 
 
 Corpus 
 trapezoldeum. 
 
 Deep transverse 
 fibres of pons. 
 
 Pyramidal bundles. 
 Superficial transverse fibres of pons. 
 
 Fig. 112. Section through the lower part of the human pons immediately above the medulla 
 
 oblongata. (Cunningham.) 
 
 268 
 
THE NERVOUS SYSTEM 
 
 a 
 I 
 
 a 
 
 270 
 
THE NERVOUS SYSTEM 
 
 Upper and fourth ventricle 
 
 Mesencephalic root of the 
 trigeminal nerve. 
 
 Medial longitudinal 
 bundle. 
 
 Formatio reticularis. 
 
 Anterior medullary velum. 
 Gray matter on floor of 
 fourth ventricle. 
 Brachium 
 
 conjunctivum. 
 Lemniscus 
 lateralis. 
 
 Commencing 
 decussation 
 of brachia 
 conjunctiva. 
 
 Lemniscus 
 medians. 
 
 Pyram- 
 idal 
 bundles. 
 
 Fig. 114. Section through the superior part of the pons of the orang, above 
 the level of the trigeminal nuclei. (Cunningham.) 
 
 272 
 
THE NERVOUS SYSTEM 
 
 Root bundle of IVth 
 Ace. motor root of Vth. 
 
 Sup. cerebell. ped. 
 
 Part of lateral fillet. 
 Dorsal long, bundle. 
 
 Ventral long, bundle. 
 
 Lateral fillet. 
 Decuss. of superior peduncles 
 
 Main fillet 
 
 Substantia nigra. 
 Central nucleus. 
 
 Crusta or pes peduncul 
 
 Breaking up of crusta Into pyramid 
 bundles. 
 
 Fig. 115. Transverse section through the uppermost part of the pons. 
 
 (Quain.) 
 
 274 
 
THE NERVOUS SYSTEM 
 
 Fig. 116. Transverse section across the mid-brain through the posterior cor- 
 pora quadrigemina. Magnified about 3% diameters. 
 
 From a photograph. (Quain.) 
 
 gr., dorsal quadrigeminal groove (sulcus longitudinalis) ; c. q. p., corpus 
 quadrigeminum posterius; str.L, stratum lemnisci; c. gr., central gray matter; 
 n. HI, IV, oculomotor nucleus ; d. V, descending motor root of fifth nerve ; 
 p.l.b., posterior longitudinal bundle; j.r.t., formatio reticularis tegmenti; 
 d. d' , decussating fibres of tegmentum (fountain-like decussations of Forel 
 and Meynert) ; s. c. p., decussating fibres of superior cerebellar peduncles; 
 /, main fillet; /', lateral fillet; pp., crusta pedunculi; s. n., substantia nigra; 
 g.i.p., interpeduncular ganglion; sy., Sylvian aqueduct. 
 
 276 
 
THE NERVOUS SYSTEM 
 
 Central gray 
 matter. 
 
 Aqueduct. 
 
 Inferior colliculus 
 
 Mesencephalic root of trigeminal nerve. 
 Nucleus of trochlear ner?e. 
 Brachiuna inferjm* 
 
 Medial longitudinal bundle 
 
 Medial lemniscus. 
 
 Brachlum 
 conjunct! vum 
 
 Basis pedunculi. 
 
 Fig. 117. Transverse section through the human mesencephalon at the level 
 of the inferior colliculus. (Cunningham.) 
 
 278 
 
THE NERVOUS SYSTEM 
 
 280 
 
 S 
 
THE NERVOUS SYSTEM 
 
 Fig. 119. Section across the mid-brain, through the anterior corpora 
 
 quadrigemina. Magnified about 3% diameters. (Quain.) 
 Sy., aqueductus Sylvii; c. p., commissura posterior; gl.pi., corpus pinealis; 
 c. q. a., gray matter of one of the anterior corpora quadrigemina ; c. g. m., 
 corpus geniculatum mesiale; e.g. I., corpus geniculatum laterale; tr.opt., 
 tractus opticus; pp., pes pedunculi ; p.l.b., posterior longitudinal bundle; 
 fi., upper fillet; r. n., red nucleus; n.III, nucleus of third nerve; ///, issuing 
 fibres of third nerve; 1. p. p., locus perforatus posticus. 
 
 282 
 
THE NERVOUS SYSTEM 
 
 an important nucleus of gray matter, the dentate nucleus. On 
 cross section it appears as a wavy, curved line concentric with 
 the surface of the hemispheres. 
 
 The central lobe possesses three other nuclei on each side of 
 the middle line. One, the nucleus fastigii, is nearest the middle 
 line and immediately above the roof of the fourth ventricle. A 
 third nucleus lies dorsal to this. It is named the nucleus globosus. 
 
 Sulcus prepyramidalls 
 
 Uvula. 
 
 Tonsilla. 
 
 Lobulus biventralis. 
 
 Sulcus intragracills 
 Sulcus postgracills. 
 
 Sulcus horizontalis magnus. 
 
 Lobulus pos- 
 
 tero-supei ior. 
 Lobulus semi- 
 
 lunaris inferior. 
 Lobulus gracilis 
 
 posterior. 
 Lobulus gracilis 
 
 anterior. 
 Pyramids. 
 
 Fig. 120. View of cerebellum from below. Natural size. (Quain.) 
 
 Between it and the dorsal border of the dentate nucleus is still 
 another nucleus, the nucleus emboliformis. (Fig. 123.) 
 
 The Destination of the Superior Peduncles of the Cerebellum 
 After decussation the majority of the fibers of the superior 
 peduncle of the cerebellum terminate in the red nucleus: The 
 upper termination of these fibers really forms a capsule to the red 
 nucleus. 
 
 The Red Nucleus The red nucleus is situated at the top of 
 
 284 
 
THE NERVOUS SYSTEM 
 
 286 
 
THE NERVOUS SYSTEM 
 
 288 
 
THE NERVOUS SYSTEM 
 
 the mid-brain, beneath and ventral to the corpora quadrigemina, 
 and dorsal to the inner portion of crura of that side. Lateral to 
 it and dorsal to the external portion of the cms is another collec- 
 tion of gray cells termed the substantia nigra. (Figs. 118 and 119.) 
 Substantia Nigra The substantia nigra is found in sections 
 below the level at which the red nucleus is formed. It separates 
 the crusta of the cerebrum from a large mass of transversely and 
 longitudinally running fibers, known as the tegmentum and con- 
 
 Fig. 123. Section across the cerebellum and medulla oblongata showing the 
 position of the nuclei in the medullary centre of the cerebellum. (Quain.) 
 n. d., nucleus dentatus cerebelli ; s, band of fibres derived from restif orm 
 body, partly covering the dentate nucleus ; s. c. p., commencement of su- 
 perior cerebellar peduncle; com', com", commissural fibres crossing in the 
 median white matter. 
 
 sisting largely of fibers making up the superior peduncles of the 
 cerebellum. 
 
 The Tegmentum Like the f ormatio reticularis the tegmentum 
 consists of many interlocking fibers, definite bundles of which 
 belong to the superior cerebellar peduncles. It also contains many 
 
 290 
 
THE NERVOUS SYSTEM 
 
 scattered nerve cells which form relay stations for some fibers 
 coming from higher and lower levels. 
 
 The New Tracts of White Fibers The important nuclei of 
 the brain stem, the medulla and mid-brain, and cerebellum, have 
 now been mentioned. It remains to describe the tracts of white 
 fibers connecting them and passing through them. It will be con- 
 venient to start with the various tracts of white matter found in 
 the spinal cord, though it must always be kept in mind that those 
 tracts which carry impulses in a descending direction are being 
 
 Nucleus of fasciculus 
 
 cuneatus. Nucleus of Commissural nucleus of ala cinerea. 
 
 t fasciculus gracilis. % Dorsal external arcuate fibres. 
 
 Restiform body. 
 
 Spinal tract of . _ 
 trigeminus. 
 
 Ventral external arcuate 
 fibres. 
 
 Fig. 124. Diagram showing the composition of the cerebellar portions of 
 the internal and external arcuate fibres. (Morris.) 
 
 tracted in a direction opposite to that in which they grow and 
 functionate, and toward the origin of the axis cylinders of which 
 they are composed. 
 
 Deep Arcuate Fibers We may start first with the posterior 
 spinal columns, the column of Burdach and Goll, carrying sensa- 
 tions of muscular sense muscular tone and reflex coordination, 
 which reach consciousness. These may be traced to their endings 
 around the cells in the nucleus cuneatus and gracilis. From these 
 nuclei other fibers are given off which pass inward and ventrally 
 through the lower half of the medulla to decussate in the middle 
 line with similar fibers of the opposite side. These fibers are called 
 the deep arcuate fibers. They turn upward after decussation, lying 
 close to the middle line and dorsal to that portion of the fibers of 
 the pons Varolii which surrounds the pyramids as they pass up- 
 
 292 
 
THE NERVOUS SYSTEM; 
 
 wards. They form a well-marked bundle in this situation called 
 
 the mesial fillet. (Figs. 124-125 and 105 to 119.) 
 
 The mesial fillet may be traced upwards through the mid-brain 
 
 where it occupies a more lateral position. Above the pons Varolii 
 
 it leaves the middle line 
 beneath the superior pe- 
 duncle of the cerebellum, 
 and at higher levels is lat- 
 eral to the decussation of 
 the superior peduncles. 
 The mesial fillet termi- 
 nates in the superior cor- 
 pora quadrigemina, in the 
 external geniculate bodies 
 and in the optic thalami. 
 Superficial Arcuate Fi- 
 bers A second set of 
 fibers are given off from 
 the nuclei cuneatus and 
 gracilis, passing externally 
 and ventrically instead of 
 internally. These are the 
 superficial arcuate fibers 
 which pass over the tu- 
 bercle of Rolando, over 
 the upper portion of the 
 olivary prominence, over 
 the pyramids, over the op- 
 posite olive and tubercle of 
 Rolando, to join the cor- 
 pus restiforme of the oppo- 
 
 Pig. 125. Diagram of the spino-cerebel- 
 lar, bulbo-tegmental, cerebello-tegmental, 
 
 ponto - tegmental, and ponto - cerebellar 
 tracts. (Quain.) 
 
 site side. A number of the 
 
 axons, particularly those springing from a little accessory cuneate 
 nucleus on the lateral surface of the main nucleus, join the resti- 
 form body of the same side. As the restiform body forms the 
 inferior peduncle of the cerebellum the ultimate termination of 
 these fibers is to the gray matter of this portion of the cerebellum. 
 They run directly to the cortex particularly of the vermis. 
 (Fig. 124.) 
 
 294 
 
THE NERVOUS SYSTEM 
 
 The Termination of the Direct and Crossed Cerebellar Tracts 
 Two more tracts in the spinal cord convey sensations of mus- 
 cular tone and muscular coordination. They are the direct cere- 
 bellar tract and the anterior cerebellar tract. The former convey 
 the uncrossed muscular sensations which do not reach conscious- 
 ness. Their axons originate in the cells of Clark's column and 
 they pass directly into the corpus restiforme and then to the cere- 
 bellum. The antero-lateral cerebellar tract carries crossed mus- 
 cular sensations which do not reach consciousness. The fibers of 
 this tract travel upward through the formatio reticularis of the 
 medulla oblongata, representing the only longitudinal spinal fibers 
 in the upper part of the pons after the removal of direct cerebellar 
 tracts and the posterior columns, with the exception of the pyram- 
 idal tracts. That portion of this tract, the posterior portion, which 
 conveys muscular sensations, leaves the medulla by bending directly 
 dorsally to join the superior peduncles of the cerebellum, passing 
 with them to the cerebellum. (Figs. 124 and 125.) 
 
 The Spino-thalamic Fibers Other bundles of the antero- 
 lateral column, the spino-thalamic fibers, convey sensations of pain, 
 of heat and cold, and of touch and pressure. These fibers form 
 the column of Gowers internal to the crossed cerebellar tract and 
 a bundle anterior to it. The two sets of fibers join the medial 
 fillet and end with this bundle in the optic thalamus. As new 
 masses of gray matter than those represented in the cord develop 
 within the medulla and mid-brain, so also new tracts of fibers are 
 found in these portions of the brain. (Fig. 125.) 
 
 The Connections of the Olive The inferior olivary nuclei 
 are directly connected by some fibers with the corpus restiforme 
 and hence with the cerebellum of the same side. Most of the 
 fibers, however, which are associated with the olivary nuclei, 
 pass across the middle line through the opposite olive and into the 
 opposite corpus restiforme. These fibers are axis cylinders of the 
 olivary bodies at least, ablation of one cerebellar hemisphere 
 will cause atrophy of the opposite olive. It is possible that some 
 of the olivo-cerebellar fibers may be efferent from the cerebellum, 
 as some fibers originating in the olivary nucleus pass directly 
 down into the cord, and after being joined with other fibers from 
 the optic thalamus help to form the thalamic or olivo-spinal tract 
 of Helweg. This tract then is a descending tract, but it has been 
 
 296 
 
THE NERVOUS SYSTEM 
 
 convenient to describe it with the other connections of the olivary 
 nucleus. (Fig. 98.) 
 
 The Various Fibers Constituting the Corpus Restifonne, or 
 Inferior Peduncle of the Cerebellum Before describing other 
 descending tracts, one other important connection to the restiform 
 body remains to be described. Some of the fibers of the vestibular 
 branch of the eighth nerve, which are connected by collaterals 
 with the nuclei of Bechterew and Deiters, form a bundle known 
 as the internal restiform 'body. The internal restiform body also 
 contains fibers from the nuclei of the glossopharyngeal nerve and 
 probably fibers running directly from the nuclei of Bechterew and 
 Deiters. This bundle joins with the arcuate fibers and passes into 
 the corpus restiforme and inferior peduncle. The following 
 bundles of nerve fibers, therefore, run to the cerebellum. 
 
 1. Fibers originating in Clark's column of cells, homolateral 
 and ascending in the direct cerebellar tract. 
 
 2. Fibers from the dorsal nuclei of the posterior columns of 
 the same and opposite side. 
 
 3. Internal and superficial arcuate fibers from the olivary 
 bodies. 
 
 4. From the vestibular nerve, the glossopharyngeal nerve and 
 Deiters nucleus. All these fibers run directly to the cortex of the 
 cerebellum, particularly the cortex of the vermis. 
 
 The Middle Peduncle of the Cerebellum, or the Pons Varolii 
 The cortex of cerebellar hemispheres receives most of its af- 
 ferent fibers from the middle peduncle. The pons Varolii is largely 
 composed of fibers which are only commissural and run from one 
 cerebral hemisphere to the other. A large number of fibers enter- 
 ing the middle peduncle are axis cylinders of cells in the formatio 
 reticularis; others are efferent and end around cells in the formatio 
 reticularis. Many fibers of the crura cerebri pass between the 
 frontal and temporal lobes, and the formatio reticularis of the 
 opposite side. It is therefore in the formatio reticularis that one 
 connection between the cerebral cortex and the cerebellum is 
 effected. 
 
 The Afferent Tracts to the Cerebellum in the Superior Pe- 
 duncle Two other afferent tracts enter the cerebellum. They 
 have been previously mentioned. One ascends from the cord in 
 the lateral part of the antero-lateral column, conducting the crossed 
 
 298 
 
THE NERVOUS SYSTEM 
 
 conscious muscular sensations and passes into the cerebellum by 
 the superior peduncle. The second arises in cells of the superior 
 corpora quadrigemina and passes into the cerebellum also by the 
 superior peduncles. 
 
 Inasmuch as the superior corpora quadrigemina receive the 
 fibers of the optic nerve, this tract must transmit association im- 
 pulses important for muscular coordination between the sense of 
 vision and the cerebellar centers, an association much used in many 
 muscular movements, few of which are not guided by sense of 
 vision. So much for the afferent tracts of the cerebellum. The 
 efferent fibers to the cells of the formatio reticularis, contained in 
 the middle peduncle, have been mentioned. 
 
 The Efferent Tracts from the Cerebellum All efferent fibers 
 from the cerebellum leave from the central nuclei, the nucleus 
 dentatum, fastigii, globosus and emboliformis. No efferent cere- 
 bellar fibers leave the cortex. A large mass of fibers leave the 
 nucleus dentatum and pass by the superior peduncle to the red 
 nucleus and subthalamic region of opposite side. A certain number 
 of fibers pass also from the central nuclei to the corpora quadri- 
 gemina of the same side. No fibers pass directly to the spinal 
 cord but important tracts run between the central nuclei and 
 the nucleus of Bechterew and Deiters. From these nuclei large 
 tracts run down to the different levels of the spinal cord in the 
 antero-lateral column constituting the vestibulo-spinal column. 
 It is doubtless in part through this tract that the impulses of 
 equilibrium are capable of affecting the motor apparatus of the 
 spinal cord, passing by way of the vestibular nerve, first to the 
 cerebellum where they become modified into impulses permitting 
 finer muscular adjustments by association with other impulses 
 within this large center of coordination where all impulses having 
 to do with muscular contraction meet. 
 
 The Trapezium and Lateral Fillet (see Figs. 102 and 126) 
 Two other tracts of white matter through the mid-brain and medulla 
 are yet to be considered. One of these connects the nuclei of the 
 auditory nerve with the inferior corpora quadrigemina. From both 
 divisions of the nuclei of the auditory nerve, the dorsal and ventral 
 nucleus, nerve fibers pass internally to decussate with similar fibers 
 of the opposite side (Figs. 105 to 116.) 
 
 This decussating tract is called the trapezium and forms a defi- 
 
 300 
 
THE NERVOUS SYSTEM 
 
 nite structure in the medulla. The trapezium is situated just 
 dorsal to the formatio reticularis. It is joined by nerve fibers 
 from the superior olive and by the fibers of the striae acusticse 
 
 Fig. 126. 
 
 A. Auditory fibres passing by way of the stria acustica, 1, and the 
 trapezium, 2, and the lateral fillet to the inferior corpus quadrigeminum, 3. 
 
 B. Vestibular fibres after making connections through the medulla pass- 
 ing to the dentate nucleus, 4. 
 
 C. Optic fibres passing to the superior corpus quadrigeminum, 5, from 
 which fibres run to the cerebellar cortex, 6, and posterior longitudinal bundle, 
 7, which in turn establishes connections with the III and IV nucleus and the 
 Vlth and the anterior horn cells, 8, by means of the antero-lateral column, 9. 
 
 D. Afferent cerebellar fibres composed of the posterior cerebellar tract, 10, 
 to the cerebellar cortex, 6, and the superficial external arcuate fibres, 11, to 
 the cortex of the vermis. The direct cuneate cerebellar fibres, 12, and the 
 olivo-cerebellar fibres, 13. 
 
 E. Efferent cerebellar fibres to the red nucleus, 14, from the dentate 
 nucleus, 4. 
 
 302 
 

THE NERVOUS SYSTEM - 
 
 after these have crossed on the floor of the medulla and fibers from 
 the auditory nucleus. All these fibers become collected into a 
 bundle which passes upwards through the mid-brain where they 
 form the lateral fillet. It lies to the outer side of the superior 
 cerebellar peduncle. It virtually passes around the peduncle on 
 its outer side and in this manner gains the inferior corpora quad- 
 rigemina in which the fibers of the lateral fillet end. (Figs. 105- 
 116.) The inferior corpora quadrigemina form substations for 
 auditory sensations. 
 
 The Posterior Longitudinal Bundle The other white tract 
 through the mid-brain and pons is the posterior longitudinal bundle. 
 It is an important bundle seen in all sections through the pons and 
 mid-brain, and continued throughout the spinal cord in the antero- 
 lateral column as the tract of Marie. (Figs. 126 and 105-116.) 
 
 The posterior longitudinal bundle is a well-defined tract run- 
 ning near the middle line just dorsal to the tegmentum in the 
 mid-brain, and to the formatio reticularis in the medulla oblongata. 
 It connects the nuclei of the various cranial nerves with each 
 other and contains, therefore, fibers which run in both directions. 
 
 Summary of the Various Substations We have now consid- 
 ered the principal new masses of gray matter which have been 
 added to the cerebrospinal axis in the hind and middle brain. 
 
 We have also followed the connections of these nuclei, and the 
 principal tracts connecting these nuclei and carrying impulses 
 from them and from the spinal cord up to them: they may be 
 termed the terminal substation of impulses, standing next to the 
 cerebrum in the receipt or transmission of impulses passing be- 
 tween the cerebrum and the lower portions of the nervous system. 
 These terminal substations are situated at different levels for 
 various white tracts in the cerebrospinal axis. In the case of the 
 pyramidal tracts the terminal substation between the cerebrum 
 and the spinal cord is in the spinal cord itself. In the case of 
 other fibers also running in the crura cerebri the terminal sub- 
 station is in the formatio reticularis. For other tracts it is in the 
 red nucleus and the corpora quadrigemina, while in the case of 
 still others the terminal station is in the base of the fore-brain itself, 
 namely in the optic thalami. 
 
 The New Masses of Gray Matter Belonging to the Fore-Brain 
 It now remains to describe the new masses of gray matter be- 
 
 304 
 
THE NERVOUS SYSTEM 
 
 o o 
 
 o o 
 
 1 
 
 o ^ 
 
 111 
 
 all 
 
 . 
 
 H .M 
 
 <N <U 
 
 bJD 
 
 306 
 
THE NERVOUS SYSTEM 
 
 longing to the cerebrum arising from what we have termed the 
 precerebral vesicles, and those paths of connection between them 
 and the so-called terminal substations placed between the cerebrum 
 and the lower portions of the cerebrospinal axis. 
 
 Lateral rentricle. 
 Caudate nucleus. I 
 Anterior commissure. '- 
 Lentiform nucleus. 
 External capsule. 
 Clanstrum 
 
 Savum septi. pellucidl. 
 Septum pellucidum. 
 Corpus callosum. 
 
 Internal capsule. 
 
 Insula. 
 
 Middle cerebral artery. 
 
 Anterior per- 
 I forated space. 
 I Optic tract. 
 
 Internal carotid artery. I Lamina terminalis. 
 
 Optic recess. Third nerve. 
 
 Fig. 128. View from the front of a coronal section of an adult brain made 
 two and a half inches behind the frontal pole and nearly one inch behind 
 the temporal pole and about half an inch posterior to the anterior end of 
 the lateral ventricles. Five-sixths. (Quain.) 
 
 The vallecula Sylvii is seen on each side external to the optic commissure; 
 on the right side of the brain the internal carotid artery is shown dividing 
 in this space into the anterior and middle cerebral arteries. 
 
 The majority of new masses of gray matter of the fore-brain 
 have already been described. They include the cerebral cortex 
 itself and the walls of the third ventricle, the structures appear- 
 ing in the lateral ventricles, the caudate nucleus and the optic 
 thalami themselves. 
 
 308 
 
THE NEEVOUS SYSTEM 
 
 ip SlS I JJ4 || *3 Bfr. * 
 
 IT? I s ! I if II SI !il 
 
 PI : yi J i 5 | S if 4 i 
 
 310 
 
THE NERVOUS SYSTEM 
 
 
 -si 
 
 -8-a 
 
 111 
 
 IP 
 
 U 
 
 -i H 
 
 rt ce 
 
 03 
 
 a .2 
 
 03 o *-> 
 
 ,3 c d 
 
 s?: 
 
 a ^ 
 
 !li 
 
 312 
 

THE NERVOUS SYSTEM 
 
 The Internal Capsule Internal to the optic thalami is the 
 third ventricle, the lateral walls of which are formed by the optic 
 thalami. A small portion of the optic thalami appears in the 
 lateral ventricle. Most of its external surface is surrounded by 
 thick, capsule-like layer of white fibers termed the internal capsule, 
 the great pathway of all afferent and efferent impulses to and 
 from the cerebrum. 
 
 The internal capsule is formed of all those nerve fibers which 
 pass from various portions of the cerebrum in the crura cerebri, 
 and in part of fibers emerging from the optic thalami to be dis- 
 
 Induseum. 
 
 Commissura hippocampi. Gyrus cinguli. j 
 
 Stria longitudinalis medialis. 
 
 ^ Cavum septl pellucidi. 
 ^f Septum pellucidum. 
 
 Ventriculus 
 "P. lateralis. 
 
 Crus fornicis. 
 
 Plexus 
 
 chorioideus 
 lateralis. 
 
 Stria terminalis. 
 
 Tela chorioidea. 
 
 Attachment of lamina 
 
 chorioidea. 
 t - Thalamus (free surface). 
 
 Tseuia thalami. 
 Plexus chorioideus vent, tertii. Ventriculus tertius 
 
 Thalamus. 
 
 Fig. 131. Diagram of transverse section across the central parts of the lateral 
 ventricles. (Cunningham.) 
 
 tributed to many parts of the cerebrum. External to the internal 
 capsule is another nucleus of gray matter termed the lenticular 
 nucleus. It is quite a large nucleus, shaped somewhat like a bicon- 
 vex lens on both transverse and horizontal section. It separates 
 the internal capsule from another layer of white fibers termed the 
 external capsule. Outside the external capsule is another nucleus 
 of gray matter, thin on transverse section, termed the claustrum. 
 
 Classification of the Cerebral Nerve Tracts The tracts of 
 white fibers of the cerebrum may be classed as nerve tracts con- 
 necting the brain with lower levels. They are afferent and efferent. 
 
 Nerve tracts connecting different portions of one cerebral 
 hemisphere. 
 
 Tracts connecting two cerebral hemispheres. 
 
 The Afferent Tracts of the Cerebrum The thalamo-cortical 
 
 314 
 
THE NERVOUS SYSTEM 
 
THE NERVOUS SYSTEM 
 
 I 
 
 
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 ! 
 
 5ga 
 
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 ^o, 
 
 111 
 
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 -i n 
 
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 St. 
 
 II 
 
 lilzi 
 
 4i 
 gl 
 
 leiB 
 
 1 
 
 tj 
 
 |1 8 J 8s 2S -** 
 
 lllii iflll^ili 
 
 c, oj 
 
 5 
 
 !i- 
 
 pi 
 >/,?/ 
 
 p. 
 
 :1! 
 
 ifn 
 
 Mif 
 is 
 
 III 
 
 d M 
 
 rt 03 t 
 
 -J "H O 
 
 ft "rj 
 
 Hi 
 
 00 S 
 
 Is. 
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 O OT3 
 ft^ O 
 
 i 
 
 I a 
 
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 I rj O 
 
 I| S " 
 
 ' _ *} <D qj 
 
 
 318 
 
THE NERVOUS SYSTEM 
 
 OX+-, -^ 
 
 : syvs^ 1 -8B!! jgm t: t) fi M 
 
 / ^s^saf !lJ 
 
 *l "I s ii '' 11 Hi g lil- 
 
 &P i gf s| |ii |g i a 5 i. 1 5 |i 1 
 
 8 I| 2 *i 1| *| 1*8 *g I]! "fi |S 10 
 
 iai " !l lllfl^j :Mll 5 Pi "i 111 
 
 IM! JriMii 
 
 hr(Sfi^i/? "Si hfl 
 
 ^-> p^ fl '-^O 1 D"O 
 
 H a & < K a- 
 
 320 
 
THE NERVOUS SYSTEM 
 
 Central fissure. 
 Posterior central gyrus. 
 
 Corpus callosum. 
 
 Fornix. 
 Anterior central gyrus. / / Later&1 ventride 
 
 Superior frontal / I / - Thalamus 
 
 Sylvian fissure. gyrus. / / / / . Caudate nucleus. 
 
 ' Internal capsule. 
 Middle frontal 
 gyrus. 
 
 Claustrum. 
 
 Inferior horn of 
 
 lat. vent. 
 Hippocampal fissure. 
 
 Optic tract. 
 Hippocampal gyrus. 
 Uncus. 
 Cerebral peduncle. 
 
 Pons. 
 
 Insula. \ 
 
 Second temporal gyrus. Pyramid of medulla oblongata. 
 
 First temporal gyrus. 
 
 Fig. 135. View from the front of a coronal section of an adult brain made 
 three inches behind the frontal pole. Five-sixths. 
 
 tracts. From all parts of the optic thalami fibers stream out into 
 the internal capsule to carry on the impulse arriving at the optic 
 thalami to all parts of the cerebral cortex. Entering the internal 
 
 322 
 
THE NERVOUS SYSTEM 
 
 capsule these fibers may be divided into a frontal, parietal, occip- 
 ital and temporal group. 
 
 The frontal fibers are contained in the anterior limit of the 
 internal capsule and run to the frontal lobe. Some of the fibers 
 pass to the lenticular nucleus and then other axons carry on the 
 impulses through the external capsule. 
 
 The parietal fibers issue from the lateral surface of the optic 
 thalami and pass to the parietal lobe through the middle portions 
 of the internal capsule. The occipital fibers form radiations called 
 the occipital radiations, and pass to the occipital lobe through the 
 posterior portion of the internal capsule, coming chiefly from the 
 pulvinar or posterior tubercle of the optic thalamus and the 
 external geniculate body. 
 
 The fibers issuing from the under surface of the optic thalami 
 pass under the lenticular nucleus to the temporal lobe and island 
 of Reil. Some of these fibers, known as the auditory radiations, 
 pass directly into the "posterior portion of internal capsule from 
 the internal geniculate body. 
 
 Functions of the Thalaino-cortical Fibers Of these various 
 afferent fibers, those passing to the parietal lobes carry onward to 
 the cortex the cutaneous and possibly muscular sensations, reach- 
 ing the optic thalami through the mesial fillet. Also among the 
 fibers of the anterior or middle portions of the internal capsule 
 are those carrying on the impulses reaching the red nucleus and 
 optic thalami by the superior cerebellar peduncles. 
 
 They must be considered as furnishing information regarding 
 the fine adjustments in muscular coordination being produced by 
 the cerebellum. The optic radiations carry visual impulse from 
 the terminations of the optic nerve in the superior corpora quad- 
 rigemina. By other fibers between the occipital cortex and these 
 basal nuclei impulses may pass from the cortex to the superior cor- 
 pora quadrigemina and thence as afferent impulses to the cere- 
 bellum. Through the auditory radiations to the temporal lobes 
 are transmitted impulses from the inferior corpora quadrigemina 
 and internal geniculate body, which nuclei receive the termination 
 of the lateral fillet directly from the auditory nucleus. 
 
 Other fibers pass between the optic thalamus and the cerebral 
 cortex by way of the corpus striatum. The larger portion of the 
 afferent fibers of this body come from the optic thalami. Other 
 
 324 
 
- Fibrse propriae. 
 
 - Pyramidal fibre. 
 
 _ .-Corona radiata. 
 
 Ganglia of sensory cranial nerves. 
 
 . A! 
 
 Nucleus of spinal tract of trigemluus. _\ 
 
 " Internal capsule. 
 
 Hypothalamic nucleus. 
 
 Fibres to hypothalamic \ 
 nucleus of same side. 
 
 Nuclei of termination of! 
 sensory cranial nerves. \ 
 
 _ _ Nucleus of fasciculus 
 cuneatus. 
 
 Nucleus of fasciculus 
 
 gracilis. 
 
 Posterior root. 
 Spinal ganglion. 
 
 _ Fasciculus cuneatus. 
 Fasciculus gracilis. 
 
 rrg. 136. Scheme of ascending or spinocerebral conduction pathways. (Morris.) 
 
 326 
 
THE NERVOUS SYSTEM 
 
 Somsesthetic area 
 of cerebral cor- 
 tex. 
 
 Caudate nucleus. 
 
 Internal capsule. 
 
 Lenticular nucleus. 
 
 Cerebral peduncle. 
 Trochlear nerve. 
 
 Medulla oblongata 
 
 Motor 
 nuclei of 
 cranial 
 nerves. 
 
 Oculo-" 
 motor. 
 
 Masti- 
 cator. 
 
 Abducens. 
 
 Facial. 
 
 Glossopharyngeal. 
 
 Vagus. 
 
 Accessory. 
 
 Hypoglossal. 
 
 Decussation of pyramids. 
 
 Lateral cerebrospinal 
 
 fasciculus. 
 Ventral cerebrospinal 
 
 fasciculus. 
 
 Ventral roots of spinal nerves. 
 Ventral white commissure. 
 
 Spinal cord. 
 
 'ig. 137. Scheme of descending cerebrospinal conduction pathways. (Morris.) 
 
 328 
 
THE NERVOUS SYSTEM 
 
 fibers arising in the corpus striatum pass in the dorsal part of the 
 crusta to the nuclei pontis of the formatio reticularis. 
 
 Connections undoubtedly exist in both directions between the 
 cortex cerebri and the nuclei of the corpus striatum. The chief 
 nucleus of the corpus striatum is the caudate nucleus. The len- 
 ticular nucleus and claustrum form similar connections. 
 
 Pyramidal Tracts The efferent tracts from the Cerebrum 
 The pyramidal tract originates as axis cylinders of the cells in 
 the ascending frontal convolution. The fibers pass downwards and 
 inwards through the white matter of the hemispheres to the in- 
 ternal capsule. In this structure they occupy the middle two- 
 fifths on transverse section. The internal capsule presents a bend 
 at the juncture of the anterior one-third and posterior two-thirds, 
 with the concavity outwards, and surrounds the lenticular nucleus. 
 Anterior to the bend the caudate nucleus lies internal to it and 
 posterior to the bend the optic thalamus lies internal to it. The 
 pyramidal fibers occupy the bend and the anterior two-thirds of 
 the portion posterior to the bend. In this portion the fibers con- 
 trolling the muscles of the head lie anteriorly, then the fibers 
 belonging to the anterior extremity, the trunk and posterior ex- 
 tremity. The pyramidal fibers finally leave the internal capsule 
 and enter the crusta or crura cerebri. These structures may be 
 viewed as the stems of the brain. In the mid-brain they lie ventral 
 to the rest of the mid-brain and diverge as they are traced upwards 
 and forwards between the mid-brain and the cerebrum, to enter the 
 latter by forming the internal capsule. The two crusta thus fork 
 to inclose between them as they enter the brain the two optic 
 thalami. (Fig. 137.) 
 
 The remainder of the mid-brain, that is the dorsal portion, 
 enters the cerebrum by passing directly into the optic thalami. 
 In the crusta the pyramidal fibers form the middle two-fifths of 
 that structure. 
 
 A small portion of the upper part of the external surface of 
 the optic thalami, above the diverging fibers of internal capsule, 
 lies free in the beginning of the descending horn of the lateral 
 ventricle. 
 
 Fronto-pontine Fibers In the anterior limb of the internal 
 capsule other nerve fibers, arising as axis cylinders of the nerve 
 cells in the frontal lobes of the brain, pass down into the mesial 
 
 330 
 
THE NERVOUS SYSTEM 
 
 portion of the crusta and end around the scattered cells in the 
 formatio reticularis. 
 
 Temporo-pontine Fibers Other efferent fibers from the cere- 
 brum arise in the temporal lobes and reach the posterior limb of 
 the internal capsule by passing under the lenticular nucleus. They 
 then reach the external division of the crusta and end in the scat- 
 tered cells of the pons. 
 
 Both the fronto-pontine and temporo-pontine fibers represent 
 efferent tracts from the cerebrum and afferent to the cerebellum 
 of the cerebro-cerebellar connections, being continued into the 
 lateral hemispheres of the cerebellum by the transversely running 
 middle peduncles. The return tract of this cerebro-cerebellar con- 
 nection is from the cortex of cerebellum to the dentate nucleus, 
 then by the superior peduncles to the red nucleus and optic thalami, 
 and finally from the optic thalami to the cerebral cortex. Part 
 of the thalamo-cortical fibers have already been described, those 
 passing directly into the internal capsule and around the lenticular 
 nucleus as the thalamo-frontal, thalamo-parietal and the auditory 
 and optic radiations. 
 
 Intra-Cerebral Association Tracts Short and long association 
 tracts exist within the cerebrum. The short tracts pass in U-shaped 
 loops between the various convolutions around the bottom of the 
 sulci. The long tracts may be divided into longitudinal tracts and 
 commissural tracts. The longitudinal tracts are: 
 
 Uncinate fasciculus Between the orbital convolutions of the 
 frontal lobes and the front part of the temporal lobes, around the 
 bottom of the fissure of Sylvius. 
 
 The cingulum From the anterior perforated space over the 
 dorsum of the corpus striatum to the hippocampus major and an- 
 terior part of temporal lobe. (Fig. 138.) 
 
 Superior longitudinal fasciculus Somewhat the same course 
 as the cingulum, connecting the frontal parietal and occipital 
 lobes. 
 
 Inferior longitudinal fasciculus External to the optic radia- 
 tion between the temporal and occipital lobes. 
 
 Occipito-frontal fasciculus Runs close to caudate nucleus in 
 outer walls of lateral ventricle. 
 
 The commissural fibers include : 
 
 (a) The great mass of cortical fibers running between the 
 
 332 
 
THE NERVOUS SYSTEM 
 
 334 
 
THE NERVOUS SYSTEM 
 
 two hemispheres and constituting the major portion of the corpus 
 callosum. 
 
 (b) The anterior commissure, connecting the two olfactory 
 lobes and portions of the two temporal lobes. 
 
 (c) Middle commissure, between the optic thalami. 
 
 (d) The hippocampal commissure, a thin lamina between the 
 diverging posterior pillars of the fornix, appears on the under 
 surface of the corpus callosum, connecting the two hippocampi 
 inajora, 
 
 FUNCTIONS AND CONNECTIONS OF THE CRANIAL NERVES 
 
 Olfactory Nerves The olfactory as the optic nerves are to be 
 viewed as cerebral associated tracts connecting the brain with a 
 more distal portion of this same organ. 
 
 Anatomically they are different from the other cranial nerves. 
 
 The olfactory nerve fibers are derived from cells situated upon 
 the surface of the body imbedded within the nasal mucous mem- 
 brane. One process, the real olfactory nerve, passes forward toward 
 the surface to end in the olfactory end sense organ. The other 
 process passes backward as a medullated nerve fiber, through the 
 cribriform plate to the olfactory bulb, where they terminate in a 
 terminal arborization among the branches of another terminal 
 arborization of the peripheral process of another nerve cell called 
 a mitral cell. 
 
 It is the axons of the mitral cells which form the olfactory 
 tracts. Each tract divides posteriorly into two roots, a mesial 
 root ending in the anterior end of the callosal gyrus of the limbic 
 lobe, and a lateral root, crossing the anterior perforated space to 
 end in the uncinate extremity of the hippocampal gyrus. Between 
 these two tracts is a prominence, the olfactory tubercle. 
 
 Portions of the Brain Forming the Olfactory Mechanism 
 The following portions of the brain serve as central nuclei and 
 association tracts of the olfactory apparatus. 
 
 (1) Olfactory bulb and tract. 
 
 (2) Anterior perforated space. 
 
 (3) Anterior portion of the uncinate gyrus. 
 
 (4) Septum lucidum. 
 
 (5) Hippocampal convolution. 
 
 336 
 
THE NERVOUS SYSTEM 
 
 (6) Anterior commissure. 
 
 (7) Trigonum habenulae. 
 
 (8) Fornix. 
 
 (9) Corpora mammillaria. 
 
 (10) The bundle of Vicq d'Azyr. 
 
 (11) Optic thalami. 
 
 Fig. 139. Diagram of the principal components of the optic apparatus. 
 
 (Morris.) 
 
 The Optic Nerve The real optic nerves are merely the short 
 processes of nerve cells, situated within the retina and passing 
 to the sensory epithelium of the retina. The central processes of 
 these nerve cells pass in the opposite direction and form the optic 
 tracts. These partially decussate in the optic chiasma in such a 
 
 338 
 
THE NERVOUS SYSTEM 
 
 manner that only the fibers from the internal half of each retina 
 cross. The optic tracts end posteriorly in the pulvinar of the 
 optic thalami, the external geniculate body and the superior cor- 
 pora quadrigemina. From these connections nerve fibers enter the 
 posterior portion of the internal capsule and pass by the optic 
 radiations to the occipital lobes. This nerve transmits visual 
 sensations. 
 
 MUM. L AT. ANT 
 (0*RKSCMeW!TSCH) 
 
 NUCl.OORS.I.(Ufl9 
 
 WOCL.VENT.I. (ANT.).. 
 
 NUCk.OOR6.ll.(>'OSl$ 
 (V.GVDOSN) 
 
 NUCU.CEHTRWJS- 
 
 ;NUCUVerr.li.(posT.) 
 
 Fig. 140. Diagram of the groups of cells forming the nuclei of the third 
 
 and fourth nerves. (Quain.) 
 
 The fibres from the nucleus of Darkschewitsch to the oculo-motor nerve 
 are doubtful. 
 
 The Third, Fourth and Sixth Nerves The third and fourth 
 and sixth nerves may be regarded as arising from one continuous 
 elongated nucleus, extending from the level of the striae acusticae 
 in the fourth ventricle to the superior corpora quadrigemina, close 
 to the middle line. 
 
 The anterior portion of this nucleus, that belonging to the 
 third nerve, may be divided into different portions, a more lateral 
 large-cell portion, a superficial small-cell portion and another 
 median portion of large cells. (Figs. 140 and 141.) 
 
 Stimulation from before backward beginning at the posterior 
 
 340 
 
THE NERVOUS SYSTEM 
 
 boundary of the third ventricle gives contraction of the ciliary 
 muscle (changing the curvature of the lens of the eye), contraction 
 of the pupil, of the internal rectus, the superior rectus, the levator 
 palpebras superioris, the inferior rectus and the inferior oblique. 
 Finally, when the nucleus of the fourth nerve is reached, we obtain 
 contraction of the superior oblique, and when the sixth nerve is 
 reached, contraction of the external rectus. 
 
 Fig. 141. Section through the upper part of one of the anterior corpora 
 
 quadrigemina and the adjacent part of the thalamus. (Quain.) 
 s., aqueduct; gr., gray matter of aqueduct; c. q. s., quadrigeminal emi- 
 nence, consisting of: 1., stratum lemnisci; o., stratum opticum; and c., stratum 
 cinereum; Th., thalamus (pulvinar) ; c.g.i., c.g.e., internal and external 
 (mesial and lateral) geniculate bodies; br.s., br.i., superior and inferior 
 brachia; /., fillet; p.L, posterior (dorsal) longitudinal bundle; r., raphe; ///, 
 third nerve; nlll, its nucleus; I. p. p., posterior perforated space; s.n., sub- 
 stantia nigra; above this is the tegmentum with its nucleus, the latter being 
 indicated by the circular area; cr., crusta; 11, optic tract; M., medullary 
 centre of the hemisphere; n. c., nucleus caudatus; st., stria terminalis. 
 
 All these nuclei, as also the endings of the optic nerves in the 
 superior corpora quadrigemina, are connected by means of the 
 posterior longitudinal bundle, so that means are provided for 
 accurate coordination, not only between the oculo-motor nuclei 
 themselves, but because many of the fibers of the posterior longi- 
 tudinal bundle are axons of cells of Deiters' nucleus, with also 
 
 342 
 
THE NERVOUS SYSTEM 
 
 the great centers of coordination of the whole body in the cere- 
 bellum. 
 
 The important tract between the superior corpora quadrigemina 
 and the cerebellum indicate that the connections of the former 
 with the optic nerves chiefly serve the function of coordination of 
 visual impulses with the movements, not only of the eye, but also 
 of the rest of the body. 
 
 The function of the oculo-motor nerves is not entirely motor. 
 They contain a large proportion of afferent fibers from the muscle 
 of the eye-ball. After total desensitization of the eye-ball by 
 cocaine or by section of the fifth nerve, the movements of the 
 eye-ball will be carried out with as much precision as under normal 
 conditions. 
 
 The Fifth Nerve The fifth nerve is loth motor and sensory. 
 It supplies sensation from the whole of the face and interior of 
 the mouth. Its motor fibers supply the muscles of mastication. 
 It also supplies the tensor tympani muscle. It contains trqphic 
 fibers. 
 
 The Seventh Nerve The seventh cranial nerve is largely 
 motor to the muscles of the face and some of the internal ear 
 muscles. Through the nervus intermedius of "Wrisberg, which is 
 usually included as part of the seventh nerve but should really 
 be considered a separate nerve containing efferent secretory fibers 
 to the submaxillary and sublingual glands and afferent fibers, con- 
 veying impulses of taste and general sensibility from the tongue 
 backwards from the geniculate ganglion. 
 
 The Eighth Nerve The eighth nerve possesses two definite 
 functions. Its auditory branch carries impulses from the sensory 
 auditory epithelium. Its fibers originate in the bipolar cells of 
 the ganglion of Scarpa. 
 
 The nerve enters the medulla immediately beneath the pons, and 
 terminates in its dorsal and its ventral nucleus. From these nuclei 
 the auditory impulses pass to the brain by way of the trapezium, 
 the lateral fillet, the inferior corpora quadrigemina and the audi- 
 tory radiations. The vestibular branch originates in the ganglion 
 of the cochlea. The peripheral processes of these cells end in the 
 sensory epithelium of the ampulla of the semicircular canals and 
 of the saccule and utricle. (Fig. 142.) The nerve enters the me- 
 dulla with the auditory division and passes to the dorsal nucleus 
 
 344 
 
THE NERVOUS SYSTEM 
 
 fci 4 
 
 j I 
 
 346 
 
THE NERVOUS SYSTEM 
 
 beneath the trigonum acusticum. It makes connections with the 
 nucleus of Dieters and Bechterew. Some of its fibers pass directly 
 to the cerebellum. The vestibular never transmits only sensations 
 of equilibrium. Thus it is that its most important connections are 
 with the cerebellum, that central mass of gray matter the chief 
 function of which is to preside over equilibrium. Through the 
 vestibulo-spinal tract the vestibular impulses affect the spinal 
 centers. 
 
 Through the posterior longitudinal bundle the nuclei of the 
 third, fourth and sixth nerves become coordinated with the ves- 
 tibular impulses, and through the superior cerebellar peduncle 
 by way of the red nucleus and optic thalamus these same impulses 
 reach the cerebral cortex and excite there efferent motor impulses 
 which may still further influence the motor mechanism of the 
 spinal cord. 
 
 The Ninth Nerve The ninth and tenth cranial nerves are 
 chiefly sensory. The central nuclei form one continuous column 
 lateral to the motor nuclei beneath the floor of the fourth ven- 
 tricle. Both these nerves contain efferent fibers arising from 
 nuclei internal and ventral to the sensory nuclei. The chief motor 
 nucleus of the tenth nerve is the nucleus ambiguus. 
 
 The following are the functions of the ninth cranial nerve: 
 
 (1) Motor to the muscles of the pharynx and base of the tongue. 
 
 (2) Secretory fibers to the parotid gland by way of the optic 
 ganglion. (3) Sensory fibers from the tongue, mouth and pharynx. 
 (4) Inhibitory fibers to the respiratory center. 
 
 The Tenth Nerve The tenth or pneumogastric nerve is the 
 longest nerve in the body. Its connections are most numerous 
 and its functions more varied and important than, perhaps, any 
 other single nerve. 
 
 Its efferent functions are: (1) Motor to the levator paiati and 
 three constrictors of pharynx. (2) Motor to larynx. (3) Inhib- 
 itory to the heart. (4) Motor to muscles of esophagus, stomach, 
 and small intestines. (5) Motor to unstriated muscle in the walls 
 of the bronchi and bronchioles. (6) Secretory to glands of stomach 
 and possibly pancreas. 
 
 Its afferent functions are: (1) Regulate inspiration, accelerate 
 and promote inspiration or increase expiration as in coughing. (2) 
 
 348 
 
THE NERVOUS SYSTEM 
 
 Depressor and pressor from heart to vasomotor center. (3) Re- 
 flex inhibition of the heart. 
 
 The Eleventh Nerve The eleventh or spinal accessory nerve 
 should not be considered as a cranial nerve. Filaments enter it 
 which take origin by series of roots coming from cells in the in- 
 terior horn of cord as low down as the sixth cervical nerve (spinal 
 portion), but continuous above with those of the accessory por- 
 tion. It is a purely motor nerve to the trapezius and sterno- 
 mastoid muscle. 
 
 The Twelfth Nerve The twelfth cranial nerve arises from 
 cells under the trigonum hypoglossi in the floor of the lower half 
 of the fourth ventricle. It is purely motor in function, supplying 
 the muscles of the tongue and those muscles attached to the hyoid 
 bone and the extrinsic muscles of the larynx. 
 
 THE FUNCTIONS OP THE VARIOUS PORTIONS OF THE BRAIN 
 
 Methods of Study Several methods are available for investi- 
 gating the functions of the brain. 
 
 (1) A knowledge of the anatomical connections of the tracts 
 within the brain furnishes in itself information upon the functions 
 of the brain which is second to none in importance. It is for 
 this reason that a detailed study of the anatomy of the brain has 
 been necessary. 
 
 (2) Considerable information upon the function of various 
 portions of the brain is available from a study of the differences in 
 the histological structure of the brain. 
 
 (3) Direct experimentation by isolation or ablation of por- 
 tions of the brain enable us to know the function of the portion 
 operated upon. 
 
 (4) The study of the symptoms of human beings affected with 
 tumors or other diseases of the brain producing its destruction. 
 
 The function of any portion of the brain must depend solely 
 upon the efferent tracts which leave it and the afferent tracts 
 entering it. 
 
 We have seen that the animal with only a spinal cord is a 
 machine for the performance of certain reflexes. The reflexes 
 involve particularly muscles belonging to the same level as the 
 stimulated afferent nerves. They are inevitable and contain no 
 
 350 
 
THE NERVOUS SYSTEM 
 
 incalculable element. The frog is best adapted for an experi- 
 mental investigation of such a character. 
 
 If we investigate in this manner the brain we begin by divid- 
 ing the bulb by a section between the medulla and pons. Such 
 an animal is called the bulbo-spinal animal. It will present cer- 
 tain phenomena not present in the spinal animal and determined 
 by the character of the afferent nerves having their nuclei in 
 the bulb. 
 
 The Afferent Impulses Received by the Medulla The bulb 
 receives : (1) Afferent impressions of taste from the tongue through 
 the nervus intermedius. (2) Through the ninth, afferent impres- 
 sions from the tongue and pharynx. (3) Through the vagus affer- 
 ent impulses from the whole alimentary canal to the ileocolic 
 sphincter and from the lungs and heart. 
 
 Efferent Impulses Passing from the Medulla It also sends 
 efferent fibers from the nucleus ambiguus to the larynx, bronchi, 
 esophagus, stomach and intestines, secretory fibers to the stomach 
 and inhibitory fibers to the heart. 
 
 The eighth nerve is divided, even if all of its nucleus is not by 
 the section. The twelfth nerve supplying the muscles of the 
 tongue is preserved. 
 
 The Bulbo-Spinal Animal and How It Differs from the Spinal 
 Animal The preservation of these additional centers makes it 
 possible for the bulbo-spinal animal to maintain those visceral 
 functions which are under the nervous control of the bulb. The 
 blood pressure will not show the great fall present in the spinal 
 animal. The animal will also continue to breathe regularly and 
 its heart rate will remain normal. All these functions may be 
 affected by appropriate stimuli. 
 
 There is, moreover, a certain, though ill defined, dependence 
 of the skeletal muscles upon the visceral functions; so that, with 
 the preservation of the visceral nervous control, there is a greater 
 stability in the response of the bulbo-spinal animal to reflexes. 
 
 It is easier to evoke movements in all four limbs. The key 
 to the situation is the preservation of visceral functions and the 
 nexus between these and the skeletal motor functions. The mech- 
 anism by which food, including oxygen, is seized, tasted, swallowed 
 and digested and its distributions in part controlled is preserved. 
 If in the frog the eighth nerve has been left intact a certain amount 
 
 352 
 
THE NERVOUS SYSTEM 
 
 of the sense of equilibrium is preserved. The animal will try to 
 right itself if laid on its back, and usually succeeds. 
 
 The Pontine Bulbo-Spinal Animal In order to investigate 
 these the brain must be divided by a section at the upper border 
 of the pons. The motor nuclei of the fifth and sixth nerves have 
 now been preserved, as have the lower nuclei of the organ of hear- 
 ing and the important organ of static sense, the nucleus of the 
 vestibular branch of the eighth nerve. Such an animal is able to 
 walk, spring and swim. "When placed on its back it immediately 
 turns over and will appreciate the rotation of a turn-table, when 
 placed upon it, by turning its eyes in the opposite direction. 
 
 The controlling influence of the cerebellum upon the independ- 
 ently excessive excitability of the lower centers is made evident 
 by its removal from the pontine-spinal animal. If after section 
 above the pons the cerebellum is also removed, the animal be- 
 comes spontaneously active, crawling about until blocked by some 
 obstacle. There is also an increased activity of the swallowing 
 reflex, anything touching the mouth is snapped at. 
 
 In the mammal there is a similar increase of reflex activity, 
 but the power of progression is not retained. 
 
 The Animal Possessing the Brain and Cord, All Below the 
 Upper Level of the Mid-Brain The Functions of the Mid-Brain 
 When the mid-brain is preserved by a section in front of the 
 anterior corpora quadrigemina, the animal will be in possession of 
 all its sensory impressions and the efferent paths to all the eye 
 muscles except the olfactory sense. In the mammal such a con- 
 dition causes ' ' decerebrate rigidity." The limbs are held more 
 or less rigidly in a position of extension and resist passive flexion. 
 The condition would appear to be due in part to the increased 
 activity of the lower centers, especially of the cerebellum, and is 
 reflex, as it is at once abolished by section of the posterior spinal 
 roots, and in part to the removal of the inhibitory impulses nor- 
 mally flowing through the cerebro-spinal tracts. It must be re- 
 membered the pyramidal tracts in the frog are represented by 
 only a few fibers. 
 
 The Animal Possessing the Optic Thalami, All the Brain and 
 Cord Below Them The preservation of the optic thalami, that 
 is, the removal of the cerebral hemispheres alone, leaves the frog 
 with all that is necessary for the response to any stimulus. Un- 
 
 354 
 
THE NERVOUS SYSTEM 
 
 less the animal is observed critically one would fail to notice any- 
 thing wrong with the animal. It sits up in its position, on inter- 
 ference jumps away, guides itself perfectly by sight. It will 
 swim about in water until it finds a support upon which it will 
 crawl out. It will crawl up an inclined board and if the inclination 
 is gradually increased until the board is rotated on its lower end, 
 the frog will crawl up one side and down the other. 
 
 The single difference between such an animal and the normal 
 animal is the entire absence in the former of spontaneous motion. 
 It is an extremely complex and, in contrast to the previously de- 
 scribed animal, an extremely accurate and well-balanced machine. 
 Every movement, however, must be provoked by a closely related 
 external stimulus. 
 
 If care has been taken to preserve the optic thalami in such an 
 animal it will occasionally show spontaneous movements, such, for 
 instance, as attempts to bury itself as if to hibernate upon the 
 approach of winter. If the optic thalami have been preserved in 
 fishes they show very little difference from the normal fish. 
 
 On the other hand, elasmobranch fishes which depend mainly 
 upon the olfactory apparatus, the removal of merely the olfactory 
 lobes and cerebral hemispheres produce almost complete paralysis, 
 even though the optic lobes and thalami are intact. 
 
 . The animal contains no incalculable element. It feels no hunger 
 or fear. The bird acts much as the frog. It is able to walk about 
 avoiding obstacles and even to fly. It is unable to recognize food 
 or enemies or its opposite sex. It shows no fear. 
 
 The whole of the cerebral hemispheres have been successfully 
 removed in a dog. It was able to walk normally and spent most 
 of the day in walking up and down its. cage. It slept soundly at 
 night. In pinching its skin it would turn around and snarl and 
 attempt to bite. It dould not recognize food, showed no fear or 
 pleasure or recognition of those who fed it. All memory was 
 gone. 
 
 Functions of the Cerebellum We have seen that there are 
 two distinct classes of afferent stimuli; we may speak of them as 
 two systems of afferent nerves. 
 
 1. Exteroceptive or stimuli coming from the surface of the 
 body or striking it from a distance. 
 
 2. Proprioceptive or afferent stimuli from the interior of the 
 
 356 
 
THE NERVOUS SYSTEM 
 
 body, the muscles, joints and tendons. This second system has its 
 head ganglion in the cerebellum. By its afferent nerves it fur- 
 nishes information as to the exact position of the limbs and the 
 degree of contraction of the muscles. As a part of this system 
 must be included the afferent stimuli entering the vestibular branch 
 of the eighth nerve, conveying those impressions of static sense 
 which have reference to the body as a whole. 
 
 The head ganglion of 
 this system is the cerebel- 
 lum. All its impressions 
 are received and properly 
 balanced against one an- 
 other in this organ and 
 just the correct efferent 
 impulses discharged to the 
 higher parts of the central 
 nervous system, but also 
 indirectly to the spinal 
 cord through the vestibulo- 
 spinal tract and the cere- 
 bro-spinal tracts, to pro- 
 duce just that proper de- 
 gree of relative contrac- 
 tion and relaxation of op- 
 posing sets of muscles 
 which will result in a per- 
 fection of coordination, not 
 
 Fig. 143. Cells of the cerebellar cortex, 
 showing the probable path of 
 
 nerve-impulses. (Quain.) 
 A, a moss-fibre (afferent) ; B, an axon of 
 a Purkinje cell (efferent); a, granules; b, 
 their axons; c, a Golgi cell; d, two Purkinje 
 cells. 
 
 only in the normal tone 
 preserved during rest but 
 also in the variations of contractions incidental to the muscular 
 activities, which are superimposed by the higher parts of the cen- 
 tral nervous system or by the pure reflexes of the spinal cord. 
 
 The Histology of the Cerebellar Cortex The cortex of the 
 cerebellum consists of the following two layers between which are 
 situated cells, called the cells of Purkinje: (Figs. 143 and 144.) 
 
 1. Molecular layer Most external, its characteristic cell is 
 star-shaped with an axon which runs parallel with the surface. 
 Prom this axon collateral fibers dip internally, to end in a regular 
 basket-like arborization around the cells of Purkinje. 
 
 358 
 
THE NERVOUS SYSTEM 
 
 2. Granular or nuclear layer It contains two kinds of cells : 
 
 (a) Small cells with dendrites and one axon which runs 
 
 straight up into the molecular layer where it bifurcates into two 
 
 branches running parallel to the surface and resting upon the tips 
 
 of the tree like arborization of 
 Purkinje's cells. 
 
 (6) Golgi's cells Cells with 
 many dendrites terminating in 
 the neighboring gray matter. 
 
 There are two sets of affer- 
 ent fibers to the cerebellar cor- 
 tex and one set of efferent fibers. 
 
 1. Moss fibers Afferent 
 fibers presenting curious thick- 
 enings and terminating by fre- 
 quent branches in the gray mat- 
 ter. 
 
 2. Tendril fibers, also affer- 
 ent ending by arborization 
 around the base of the cells of 
 Purkinje. 
 
 3. Axons of the cells of 
 Purkinje run down into the 
 white matter to end around the 
 cells of the deep nuclei. No ef- 
 ferent fiber from the cortex of 
 the cerebellum leaves the cere- 
 bellum. 
 
 The cells of Purkinje are 
 large, flask-shaped cells with one 
 apical dendrite and one axon 
 
 Fig. 144. Section of cortex of cere- 
 bellum. (Quain.) 
 
 a, pia mater; b, external layer; c, 
 layer of corpuscles of Purkinje; d, 
 inner or granule layer; e, medullary 
 centre. 
 
 from the base of the cell. The 
 (H one dendrite is characterized by 
 the richness of its branching. 
 
 The Afferent Tracts to the Cerebellum by Way of the Three 
 Peduncles The afferent tracts of the cerebellum are : 
 
 Inferior Peduncle (1) Axons of Clark's column of cells by 
 posterior cerebellar tract. 
 
 (2) From the nuclei gracilis and cuneatus of the same and 
 opposite side. 
 
 360 
 
THE NERVOUS SYSTEM 
 
 (3) From vestibular nerve directly and indirectly from 
 Deiters' nucleus. 
 
 (4) Inferior olive of chiefly the opposite side. 
 
 Middle Peduncle Partly afferent and partly efferent to and 
 from the formatio reticularis. By means of the nuclei of the 
 formatio re.ticularis connections are established between the frontal 
 and temporal lobes of the brain. 
 
 Superior Peduncle (1) From the superior corpora quad- 
 rigemina to the cortical gray matter, and thus connections are es- 
 tablished between the optic nerve and oculo-motor and the cere- 
 bellum. 
 
 (2) The anterior cerebellar tract from the spinal cord. 
 
 The Efferent Tracts from the Cerebellum From the roof 
 ganglia the impulses from the termination of the axons of the cells 
 of Purkinje are passed on to the pons by the middle peduncle and 
 by the superior cerebellar peduncle to the red nucleus and subthal- 
 amic region. Fibers also pass from the roof nuclei to the superior 
 corpora quadrigemina. 
 
 No tract runs directly from the cerebellum to the cord, but 
 from Deiters' nucleus, which is closely connected with the roof 
 nuclei of the cerebellum, fibers run downward to the cord in the 
 vestibulo-spinal tract. 
 
 Muscular movements may be excited by stimulation of the 
 cerebellum. Unless very strong stimuli are applied to the cortex 
 of the cerebellum no movements are excited. It is not likely, 
 therefore, that any of the cerebellar efferent fibers leave the cortex. 
 On the other hand, when weak stimuli are applied to the central 
 nuclei movements are excited. Stimulations of the roof nuclei 
 will produce movements of the eyes and head. 
 
 Stimulation of the nuclei of the lateral lobes, the nucleus 
 dentatum, will produce movements of the trunk and limbs. The 
 movements evoked are concerned in maintaining equilibrium and 
 involve every muscle of the body. 
 
 Behavior of the Cerebellarless Animal The functions of the 
 cerebellum are made more clear by removing it in whole or in 
 part. Complete unilateral extirpation of the cerebellum leaves the 
 animal (e. g., the dog) with three cardinal symptoms: 
 
 (1) Asthenia or loss of power on the same side of the body. 
 
 (2) Atonia considerable loss of tone on the same side. 
 
 362 
 
THE NERVOUS SYSTEM 
 
 (3) Astasia, tremors, or rhythmical movements, accompany- 
 ing any voluntary movement. A dog deprived of the cerebellum 
 upon one side at first is unable to stand but later acquires the 
 power to walk, though the hind leg drops and tremors accompany 
 every movement. The animal tends to fall toward the side of the 
 lesion. It attempts to support itself against any wall or support. 
 When the whole cerebellum has been removed the animal is unable 
 to walk for months. After a time it learns to do so but shows 
 an ataxia which is quite different from spinal ataxia and may best 
 be described as a top-heavy ataxia. It is an ataxia precisely similar 
 to the staggering of a drunken man. The compensation, which is 
 acquired after cerebellar lesions, is of cerebral origin. Subsequent 
 removal of the hemispheres produces permanent inability to walk. 
 The animal or human being without a functionating cerebellum is 
 without those impulses which normally constantly stream out from 
 it in response to the afferent impulses of the proprioceptive system 
 and either directly or indirectly reach the cord. 
 
 In attempting to furnish an explanation of the symptoms of 
 the cerebellarless animal a number of possibilities are present, all 
 of which are possible factors. We have in the first place not merely 
 an interruption of a large portion of the impulses conveying mus- 
 cular sensations and of proprioceptive impulses of equilibrium 
 through the vestibular nerve to the cerebellum, but also a loss 
 of what is of greater importance : the operations of the mechanism 
 which gathers up all the afferent impulses expressing the state 
 of contraction of the individual muscles and the relation of the 
 center of gravity of the whole body to its position, and which sends 
 out as its response to these incoming muscular impulses a constant 
 call upon the apparatus of the more peripheral portion of the ner- 
 vous system for just the right degree of contraction and relaxation, 
 or of augmentation and inhibition, which affords the tone of rest 
 and the steadying of the changing phases of muscular activities. 
 
 In response to the same incoming impulses there passes to the 
 higher portions of the nervous system a unified call as though from 
 the operations of a clearing-house, for the correct adjustment of 
 voluntary movement to the preservation of the desired position of 
 the center of gravity. The failure in this apparatus leaves the 
 animal without its most important guide in the adjustment of its 
 movements. In its absence the animal must fall back upon the 
 
 364 
 
THE NERVOUS SYSTEM 
 
 cerebrum which is incompletely furnished with proprioceptive 
 muscular sensations and which lacks that superlative degree of 
 association of all tracts concerned in muscular movements which 
 exists in the cerebellum. 
 
 Attempts have been made to show by some observers that the 
 normal activity of the cerebellum is exerted rather on the side of 
 augmentation of muscular function (Starling) and by others on 
 the side of restraint of muscular function (Meyers, J. A. M. A., 
 LXV, 16, 1348). The latter idea explains better the condition of 
 decerebrate rigidity following section of the mid-brain anterior to 
 the superior corpora quadrigemina, the symptom of adiadokocinesis, 
 and the spontaneous activity of the frog after removal of the cere- 
 bellum and section of the brain in front of the pons. 
 
 However this may be, the greatest emphasis should be laid on 
 the fact that the supreme function of the cerebellum is the exercise 
 of a control over muscular contraction, which control has, so to 
 speak, for its aim the production of a perfect coordination in both 
 states of rest and states of changing muscular activity. 
 
 In states of rest coodination is provided for through the more 
 direct spinal relations of the cerebellum and during voluntary 
 muscular activity, no impulse may descend from the brain without 
 an influence upon its direction being imparted to it, both in its 
 incipiency as a result of the cerebrally afferent impulses from the 
 cerebellum and in its course as a result of the lower indirect efferent 
 cerebellar connections with the lower spinal centers. 
 
 The cerebellarless animal shows three principal symptoms which 
 are all referable to the same side in unilateral ablations : 
 
 1. Asthenia a slight loss of power or weakness. 
 
 2. Atonia or loss of tone; a constant undue laxness of the 
 muscles, in other words. 
 
 3. Astasia tremors or rhythmical movements of the muscles 
 accompanying every willed movement. 
 
 All these three symptoms can be traced to the failure of normal 
 degree of responsiveness of the muscles. Each contraction starts 
 in a more relaxed muscle and therefore at less advantage, and 
 so must require an extra voluntary effort to accomplish the same 
 end. For this reason there is apparent weakness of the muscles : 
 during rest an undue laxness and during movement a frequent 
 under or over contraction, which results in tremors and inaccura- 
 
 366 
 
THE NERVOUS SYSTEM 
 
 cies of the movement to the desired end. This inaccuracy has 
 its origin not only in the unpreparedness, so to speak, of the 
 muscles, but in the loss of the organ of accurate coordination. 
 
 The cerebellarless animal will at first be unable to stand or 
 walk, but after several months may again be able to walk. The 
 compensation is cerebral, as when the cerebrum is then cut off, 
 permanent paralysis follows. The gait, however, of such a cere- 
 bellarless animal is characteristic. There is a constant tendency, 
 precisely as in a drunken man, for the center of gravity to fall to 
 one or -the other side. It is a top-heavy ataxia. The animal is 
 ever ready to take advantage of a wall against which it may lean 
 during its progression. In order to correct this tendency for the 
 center of gravity to fall to one side or the other, it makes its base 
 of support as wide as possible. Each diagonal movements starts 
 with less advantages and is accomplished with less accuracy than 
 under normal condition. 
 
 There is then a tendency for the feet to move too little, in 
 order to place the center of gravity in a correct position for bal- 
 ancing. This tendency must be corrected by an extra and usually 
 an inaccurate effort on the part of the cerebrum, so that exces- 
 sive movements are made which cause the animal to adopt a wide 
 base of support and to stagger. 
 
 This form of ataxia is called cerebellar ataxia. 
 
 It must be distinguished from two other forms of ataxia: (1) 
 spinal or tabetic ataxia, accompanying lesions in the posterior 
 columns of the cord, and (2) ataxia due to lesions in the pyram- 
 idal tracts. 
 
 In spinal ataxia the movements are excessive and inaccurate be- 
 cause the cerebrum is not furnished with information as to the de- 
 gree of contraction within the muscles. It consequently can only 
 know the results of its efforts by the use of the eyes. The loss of 
 this information produces the impression, so to speak, on the cere- 
 brum that a greater degree of movement is required than the cus- 
 tomary amount for the desired end. 
 
 In addition, therefore, to the movements being inaccurate they 
 are excessive. The cerebellar and vestibular mechanism, however, 
 is intact and so there is not that loss of the adjustment of move- 
 ments of the body as a whole to the correct position of the center 
 of gravity experienced in cerebellar ataxia. A lesion in the pos- 
 
 368 
 
THE NERVOUS SYSTEM 
 
 terior columns illustrates defects dependent on a loss of one kind of 
 function presided over in part by the cerebellum. 
 
 On the other hand, in lateral sclerosis, in which condition the 
 lesion is in the pyramidal tracts, the cerebrum has lost the main 
 path for both the activation and control of the motor mechanism 
 of the spinal cord, and, in consequence, every reflex is exaggerated. 
 
 FUNCTIONS OF THE CEREBRUM 
 
 The Contrast between the Animal Possessing a Cerebrum and 
 One Without a Cerebrum When we investigate the functions of 
 the cerebrum we at once are struck with a very important difference 
 between the animal possessing a cerebral hemisphere and one with- 
 out one. An animal deprived of its cerebral hemispheres can be 
 played upon at will ; a definite response will always follow a definite 
 stimulus. With an animal possessing a cerebral hemisphere it is 
 impossible to foretell just what response will follow any stimulus. 
 En other words the response following a peripheral stimulus always 
 is incalculable. Such an animal is influenced by many feelings in- 
 volved in the action of its consciousness. Fear, anger, hunger, affec- 
 tion, will all cause a modification of stimulated reflexes. The ques- 
 tion suggests itself, and did long ago when this subject was first con- 
 sidered, are certain areas in the cerebral cortex devoted to the 
 exclusive origination of these various impulses or feelings which 
 control our actions ? On both theoretical and experimental grounds 
 the cerebral cortex cannot be thus divided into areas which repre- 
 sent the various predominating states which characterize our con- 
 sciousness. 
 
 The Foundation of all Mental Activity upon Association of 
 Ideas (Association of Intracerebral Groups of Impulses) Abla- 
 tion of various portions of the brain does not remove any one form 
 of activity characterizing our intelligence, but rather induces a 
 reduction of intelligence as a whole. The whole science of phrenol- 
 ogy has no basis in fact. On the other hand certain portions of the 
 brain are intimately associated with definite forms of cerebral activ- 
 ity, but only with those forms of cerebral activity which, if we may 
 be excused for using the term, stand immediately next to the out- 
 side world on both the afferent and efferent end of the chain of links 
 which constitutes perception, judgment, volition and finally action. 
 
 370 
 
THE NERVOUS SYSTEM 
 
 The afferent and efferent end of this chain may be characterized as 
 perception and action. 
 
 The intervening forms of cerebral activity, upon which judg- 
 ment and volition are based, those which determine what action 
 shall follow what is perceived, call into activity many parts of the 
 cerebral cortex and are only possible because of the faculty called 
 memory. But what is memory ? Only repetition of former experi- 
 ences within the mind, the actual use of all the old previously well 
 worn cerebral paths used in former experiences minus the actual 
 external afferent impulses normally associated with these experi- 
 ences. 
 
 The association tracts constitute the old paths and the old ex- 
 periences cannot again be actuated in the mind without the use by 
 the brain of all the association tracts in the brain which were util- 
 ized in those former experiences, and by again bringing into rela- 
 tion with each other portions of the brain directly connected with 
 perception and action, though these portions may be very distant 
 from one another. And so it is that all the brain is used in most 
 of our intellectual acts and states of consciousness. 
 
 The Localization of Function in the Perceptive and Action End 
 of the Chain of Cerebral Activities All in the above paragraph 
 is very far from meaning that no portions of the brain are definitely 
 related to certain forms of cerebral activity. It is, however, only 
 the perception and action end of the chain of cerebral events which 
 can be identified with special areas within the cerebral cortex. Let 
 us consider first the areas representing action, which term we may 
 select to describe the function of the motor areas. The motor areas 
 of the human brain are all within the ascending frontal convolution. 
 From above downwards are centers which control the movements 
 of the leg, body, arm and face. (Figs. 145-147.) 
 
 Stimulation of this region will produce coordinated movements 
 of the leg, trunk, arm and face. In the dog and lower animals these 
 areas are not so sharply separated as they are in the higher apes or 
 in a human being. Indeed in the human being these areas are even 
 separated by unresponsive spaces or partitions. The areas may be 
 stimulated by weak electrical currents directly applied. In con- 
 trast to the cerebellum only weak currents are required, even 
 smaller than is needed to stimulate the underlying white matter 
 after removal of the gray matter. 
 
 372 
 
THE NERVOUS SYSTEM 
 
 Abdomen 
 
 Opening 
 
 ffjdUtS 
 
 Kxhl 
 
 corcfs. 
 
 Mastfcacton 
 
 Fig. 145. Brain of a chimpanzee (Troglodytes niger). Left hemisphere viewed from side 
 
 and above so as to obtain as far as possible the configuration of the sulcus centralis 
 
 area. 
 
 The figure involves, nevertheless, considerable foreshortening about the top and bottom 
 of sulcus centralis. The extent of the "motor" area on the free surface of the hemisphere 
 is indicated by the black stippling, which extends back to the sulcus centralis. Much of 
 the "motor" area is hidden in sulci; for instance, the area extends into the sulc. centralis 
 and the sulc. precentrales, also into occasional sulci which cross the precentral gyrus. The 
 names printed large on the stippled area indicate the main regions of the "motor" area. 
 The names printed small outside the brain indicate broadly by their pointing lines the re- 
 lation topography of some of the chief subdivisions of the main regions of the "motor" 
 cortex. But there exists much overlapping of the areas and of their subdivisions which 
 the diagram does not attempt to indicate. 
 
 The shaded regions, marked "EYES," indicate in the frontal and occipital regions re- 
 spectively the portions of cortex which, under faradization, yield conjugate movements of 
 the eyeballs. But it is questionable whether these reactions sufficiently resemble those of 
 the "motor" area to be included with them. They are therefore marked in vertical shad- 
 ing instead of stippling, as is the "motor" area. S.F., superior precentral sulcus. LPr., 
 inferior precentral sulcus. (Sherrington.) 
 
 374 
 
THE NERVOUS SYSTEM 
 
 This fact demonstrates that the cerebral cortex itself and not the 
 underlying white matter is being stimulated. The fact is further 
 attested to by the absence of the power to stimulate the cortex after 
 
 SuU.Central. 
 
 Sttlccattoso 
 mon 
 
 Sulc.parUCo 
 
 Sulc.precentrmarg. 
 
 Sulc.cdlcarin 
 
 C.S.S. del. 
 
 Fig. 146. Brain of a chimpanzee (Troglodytes niger). Left hemisphere; 
 
 mesial surface. 
 
 The extent of the "motor" area on the free surface of the hemisphere is 
 indicated by the black stippling. On the stippled area "LEG" indicates that 
 movements of the lower limb are directly represented in all the regions of 
 the "motor" area visible from this aspect. Such mutual overlapping of the 
 minuter sub-divisions exists in this area that the diagram does not attempt 
 to exhibit them. The pointing line from "Anus, etc.", indicates broadly the 
 position of the area whence perineal movements are primarily elicitable. 
 
 Sulc. central, central fissure; Sulc. calcarin., calcarine fissure; Sulc. parieto 
 occip., parieto-occipital fissure; Sulc. calloso marg., calloso-marginal fissure; 
 Sulc. precentr. marg.. pre-central fissure. 
 
 The single italic letters mark spots whence, occasionally and irregularly, 
 movements of the foot and leg (ff), of the shoulder and chest (s) and of the 
 thumb and fingers (h) have been evoked by strong faradization. Similarly 
 the shaded area marked "EYES" indicates a field of free surface of cortex 
 which under faradization yields conjugate movements of the eyeballs. The 
 conditions of obtainment of these reactions separates them from those char- 
 acterizing the "motor" area. (Sherrington.) 
 
 it has been painted with cocaine or after the administration of 
 chloral. Moreover the latent period after stimulating the gray 
 matter is longer (.065 second) than when the white matter is di- 
 rectly stimulated (.045 second). 
 
 376 
 
THE NERVOUS SYSTEM 
 
 Characteristics of Movements Excited in the Cerebrum By 
 
 stimulation of the cortex coordinated movements, precisely similar 
 to normal voluntary movements are elicited. This fact, of course, 
 means that the normal tone of some muscles must be inhibited. This 
 inhibition is absent during strychnine and tetanus poisoning so that 
 
 Frontal 
 association 
 
 Parietal 
 
 association 
 
 area 
 
 Temporo-occipital 
 association area 
 
 Parietal 
 
 .association 
 
 area 
 
 Frontal 
 
 association 
 
 area 
 
 Temporo-occipital 
 association area 
 
 B 
 
 Fig. 147. Diagrams suggesting the general motor, general and special sensory 
 
 and the association areas of the convex and mesial surfaces 
 
 of the cerebral hemisphere. (Morris.) 
 
 under the influence of these drugs only movements are obtained 
 which represent those of the stronger set of muscles. 
 
 The part played by inhibition is well illustrated by the eye 
 movements. When the convex surface of the inferior frontal con- 
 volution on the right side is stimulated both eyes turn toward the 
 
 378 
 
THE NERVOUS SYSTEM 
 
 left. This movement can only take place in the right eye by a 
 simultaneous relaxation of the right external rectus and contraction 
 of the right internal rectus and the reverse of these events in the 
 left eye. After division of all the muscles of the right eye except 
 the external rectus the eye will be constantly turned outward. The 
 same stimulus applied now will cause a sufficient relaxation of the 
 right external rectus to permit of the eye returning to the middle 
 line. 
 
 These eye movements further illustrate the bilateral effect of 
 certain unilateral cortical stimulation. In other words they illus- 
 trate that every movement originating in the cortex is a purpose 
 movement. 
 
 The Contrast and Interaction between the Control over Move- 
 ment Exerted by the Cerebrum and Cerebellum The cerebellum 
 also plays an important part in this same control. Both organs 
 participate in the maintenance of muscular tone and both are able 
 to do so by inhibition; but it is the special function of the cere- 
 bellum to maintain that constant tone which is essential to attitude 
 while the cerebrum is responsible for changing activity. 
 
 The cerebellum may be spoken of as the automatic agent of the 
 brain in the influence which it exerts in response to sensory im- 
 pulses, while the cerebrum is the voluntary agent; the cerebellum 
 is the special center for continuous muscular contraction, while the 
 cerebrum is the center for changing movements and may be played 
 upon by other afferent impulses leading to voluntary contraction as 
 well as by impulses through the proprioceptive system. The cere- 
 bellum may be viewed as a special receiving organ for propriocep- 
 tive impulses, where these impulses find a mechanism capable of 
 passing on to the rest of the central nervous system impulses, re- 
 sulting in equilibrium and normal muscular tone. To a large 
 degree these efferent impulses from the cerebellum pass through the 
 cerebrum which in turn uses the cerebellar mechanism, as a pre- 
 pared, accurately adjusted and sensitive mechanism for the produc- 
 tion of an automatic unconscious coordination. The cerebrum gives 
 direction to this coordination in the voluntary changes of activity 
 for which it alone is responsible. 
 
 The Difference in the Functions of the Cerebral Motor Areas in 
 Man and in the Animal Effects of removal of the motor centers 
 are very different in man and in animals even so high in the scale 
 
 380 
 
THE NERVOUS SYSTEM 
 
 of life as the dog. In the dog the first effect of the removal of the 
 motor area is a very severe disturbance of the dog's power of move- 
 ment. The muscles on the side opposite to the operation are much 
 weaker. Recovery takes place after a few weeks, such complete 
 recovery that the animal can be taught new movements involving 
 the use of the affected limb. 
 
 In the monkey recovery is less complete. There is some perma- 
 nent awkwardness and the immediate effect is one of absolute par- 
 alysis. 
 
 In man lesions of the motor area produce still more serious 
 effects. There is absolute paralysis at first and only a very trivial 
 amount of recovery, if the pathological condition can be removed. 
 The amount of recovery will be inversely proportional to the 
 amount of the motor area destroyed by the lesion or its operative 
 removal. 
 
 These graded consequences of destruction of the motor area 
 among animals and man are another illustration of the shifting of 
 nervous activities as we ascend the scale of life from that region 
 where they are necessitated by direct paths and few association 
 tracts, activities that may be characterized by the word fateful, to a 
 region where they are conditioned by any one set of a host of affer- 
 ent impulses reaching the regions in question along any set of 
 numerous association tracts which all together make consciousness 
 possible. 
 
 In man there exists the possibility of a greater variation in 
 response, or, in other language, a greater variety of movements. 
 Actions become based on motive and new cerebral activities impos- 
 sible in the animal are learned. 
 
 In man all must be learned at the expense of education. Man 
 comes into the world with comparatively few laid down paths. For 
 many years, as a reactive organism, he is far inferior to the lower 
 animals. It is, however, only in virtue of this fact that in him a 
 greater adaptation of action to intelligent needs becomes possible. 
 
 The Dependence of the Motor Area upon Different Impulses to 
 it In speaking of the motor area as a center for voluntary im- 
 pulses we must not consider that the whole chain of events leading 
 to a movement occurs in the motor area, or that all movements arise 
 there. Like the cells in the anterior horns of the spinal cord the 
 cells of the motor area are utilized as the last chain in a series of 
 
 382 
 
THE NERVOUS SYSTEM 
 
 cerebral events and are played upon by other impulses partici- 
 pating in the complex mechanism which alone makes possible choice 
 of action. 
 
 The Receiving End of the Mechanism Having discussed the 
 motor or discharging mechanism, let us turn to the other end of the 
 chain of cerebral events, the receiving mechanism. Of first im- 
 portance is that region of the brain which is most closely related 
 to the perception of tactile and muscular sensibility. Many facts 
 indicate that the ascending parietal convolution is the seat of 
 
 AWDITOR.Y 
 
 Fig. 148. Outline drawing of the external surface of the hemisphere. Shaded 
 
 portion represents the receptive area for tactile, 
 
 auditory and visual sensations. 
 
 the direct perception of tactile and muscular sensibility. (Figs. 
 148 to 149.) 
 
 (1) Widespread lesions in the motor area will not only produce 
 paralysis but more or less complete hemi-anesthesia. 
 
 (2) Lesions posterior to the fissure of Rolando including the 
 posterior central convolution, the superior and inferior parietal, 
 and the supramarginal convolutions are characterized by more pure 
 disturbances of sensation. 
 
 (3) In the same manner certain more posterior lesions of this 
 and the motor area of the brain, causing Jacksonian epilepsy, may 
 be preceded by sensory aura. The sensory areas are less definitely 
 located than the motor areas and may overlap and in part invade 
 
 384 
 
THE NERVOUS SYSTEM 
 
 the motor area. The sensory perceptions located in this region of 
 the brain include the sense of pressure, of temperature and the 
 muscular sense that is all sensations involved in stereognostic per- 
 ception. The sense of pain is not included in this perception. It 
 includes only those single perceptions which are needed for the 
 perception of form, size and solidity. Lesions in region mentioned 
 cause chiefly a disturbance of stereognostic perception, a symptom 
 named astereognosis. With these lesions the sense of pain is little 
 if at all affected. Even in tabes dorsalis there is atrophy of the 
 posterior central convolution. 
 
 OLFACTORY Afc.E.A. 
 
 Fig. 149. Inner surface of the same hemisphere. 
 
 The impulses of these sensations ascend in the mesial fillet to 
 the optic thalamus and pass thence by a new set of fibers through 
 the hinder limb of the internal capsule to the parietal region. 
 
 The thalamus, however, sends fibers to other portions of the 
 brain. Cortical lesions of the central convolutions never produce 
 complete hemianesthesia, so that while the posterior central or 
 ascending parietal convolution is the chief cerebral receiving station 
 for tactile and muscular sensations, widely separated other portions 
 of the brain may participate in this function. 
 
 Visual Perception This is located in the occipital lobe, in the 
 cuneus and convolutions bordering the calcarine fissure. Very defi- 
 nite evidence exists in support of this fact. 
 
 386 
 
THE NERVOUS SYSTEM 
 
 (1) Excision of one occipital lobe causes crossed hemianopsia, 
 i.e., blindness in the half of each retina which is opposite to that 
 of the extirpated lobe. This bilateral effect is explained by the 
 manner in which the optic fibers cross in the optic chiasma. 
 
 (2) Stimulation of the occipital lobe in an animal causes the 
 eyes to move toward the opposite side because of a revival of past 
 visual sensations. 
 
 (3) The eyes will move downward and to the opposite side if 
 the upper part of the occipital lobe is stimulated and upward and 
 to the opposite side if the lower portion of occipital lobe is stim- 
 ulated. 
 
 (4) From the hinder end of the pulvinar and external genicu- 
 late body which receive the optic nerves, fibers arise which pass 
 through the hinder end of the internal capsule and, as the optic 
 radiations, to occipital lobes. 
 
 (5) Pathological lesions fully confirm these conclusions. 
 Perception of hearing Situated in the superior temporal con- 
 volution; but probably not entirely here. 
 
 (1) Extirpation of the superior temporal convolution in mon- 
 keys produces marked disturbances, but not a complete disturbance 
 of hearing. 
 
 (2) Cortical lesions of the superior temporal convolution in man 
 produce varying degrees of deafness. 
 
 (3) Stimulation of the superior temporal convolutions will 
 cause animals to prick up their ears as if sounds were heard. 
 
 (4) From the auditory nucleus in the medulla nerve fibers pass 
 to the trapezium, and thence by the lateral fillet to the inferior cor- 
 pora quadrigemina. From this body and the internal geniculate 
 body they pass into the hinder parts of the internal capsule and 
 thence as the auditory radiations to the superior temporal convolu- 
 tions. The fibers from the two internal geniculate bodies decussate 
 across the middle line in Guddens' commissure which form the pos- 
 terior fibers of the optic chiasma. 
 
 Smell and Taste Perception is located in the hippocampal gyrus, 
 the dentate convolution and in that portion of the limbic lobe known 
 as the gyrus fornicatus which immediately borders the superior 
 surface of the corpus callosum. Among animals the sense of smell 
 is a far more important sense than in man. Its connections are, 
 therefore, widespread. In man it is only natural to expect that the 
 
 388 
 
THE NERVOUS SYSTEM 
 
 same widespread connections should exist and, perhaps, be all the 
 less well defined on account of the contemporaneous huge develop- 
 ment of the rest of the brain and the corresponding disappearance 
 of the acuteness of the perception of smell (see Fig. 147). 
 
 Electrical stimulation of the hippocampal convolution has 
 caused movements of the lips and nostrils. Ablation experiments 
 
 Broca area third inf. frontal 
 , co-ordination of speech muscles. 
 
 Ascending parietal convol. motor 
 / area for hand graphic images. 
 
 Ascending parietal 
 
 r motor area for 
 
 ' mouth and larynx. 
 
 Supramarginal 
 convol. 
 auditory 
 word images. 
 
 Visual 
 area 
 cuneus. 
 
 Sup. temp, convol. ' 
 auditory area. 
 
 Mid. temp, convolution 
 word understanding. 
 
 Fig. 150. Convex surface of left cerebral hemisphere and diagrammatic 
 presentation of the areas suggested as concerned with speech. (Morris.) 
 
 have not given much information. The most valuable information 
 is to be derived from the connections in the lower animals. In addi- 
 tion to the portions of the brain which we have mentioned, the pos- 
 terior part of the inferior surface of the frontal lobe and the olfac- 
 tory lobe and the anterior commissure must be included. 
 
 Association Areas and the Significance of Association of Cere- 
 bral Impulses and Their Relation to Thought and Speech The 
 areas of the brain which we have identified with perception and 
 action occupy a comparatively small amount of the cortex of the 
 brain. 
 
 390 
 
THE NERVOUS SYSTEM 
 
 Inasmuch as the cerebral processes transpiring within these 
 areas cannot be unraveled, they have been termed the silent areas, 
 and as the living being rises in the scale of intelligence these areas 
 become relatively larger. They make up by far the larger portion 
 of man's brain. 
 
 When we attempt to analyze the cerebral processes accompany- 
 ing a single combination of sensations and the infinite variety of 
 cerebral processes representing the result of the influence of these 
 sensations collectively, it is quite evident that even simple forms of 
 cerebral activity are very intricate. Thinking is only possible 
 because of man 's power to quickly call into use, or in other words 
 to associate, many portions of the brain which have to do with pre- 
 vious sensations. So intricate does this activity become that a large 
 part of the advantage of the means for this association becomes lost 
 without provision for cerebral short cuts. The association itself is 
 primarily accomplished by connecting neurons and the process of 
 association of impulses or a set of impulses which have been linked 
 together as a unit (such a unit often constituting a concept or idea) 
 is facilitated by the laying down of other fibers or even tracts which 
 furnish short cuts and which make possible the more rapid revival 
 of not only past perceptions as they happen to be related to a par- 
 ticular stimulus starting the cerebral activity, but also whole groups 
 of perceptions, taken as a whole. 
 
 The Grouping of Perception Made Possible by Speech These 
 short cuts, therefore, make possible education and memory. 
 
 Speech In the development of man the rapid association of 
 groups of impulses constituting concepts has been greatly facili- 
 tated by the adoption of audible symbols for concepts. By this 
 invention man has rendered possible, as a result of his greater power 
 of association and his power of phonation, an almost indefinite 
 enlargement of the power of reviving instantaneously past associa- 
 tions of great complexity. Upon this invention alone depends our 
 power of intricate thinking. 
 
 The Varieties of Aphasia Various disturbances of the power 
 of speech demonstrate more closely the cerebral processes upon 
 which it is based. A number of different forms of aphasia have 
 been described. 
 
 (1) Motor Aphasia This form of aphasia has been described 
 as an inability to speak though the individual understands every- 
 
 392 
 
THE NERVOUS SYSTEM 
 
 thing which is said to him and suffers no impairment of his intelli- 
 gence. This form of aphasia has been for a long time associated 
 with a lesion in the third left frontal convolution immediately an- 
 terior to the lower end of the ascending frontal convolution. This 
 area has been called Broca 's area, after the man who first described 
 the aphasia and its associated lesion. The traditional association of 
 motor aphasia with a lesion in the third left (right-handed people) 
 convolution has been so strong that few clinicians do not accept it 
 outright. Nevertheless the association will not bear investigation. 
 Theoretically it should not. The complex character of all the asso- 
 ciations necessary to speech cannot be grouped in one center of the 
 brain, and the same argument contradicts with equal force the too 
 strict localization of sensory aphasia with the area of Wernicke. 
 
 Undoubtedly near Broca 's area in the cortex are the motor cen- 
 ters for the muscles of the larynx, but the majority of cases of motor 
 aphasia are really a species of anarthria, and upon autopsy are' 
 found to be associated with lesions in other locations particularly 
 in the external capsule and the anterior portion of the internal 
 capsule. No good ground exists for distinguishing between motor 
 aphasia, when intelligence is unimpaired, and the type of aphasia 
 described below by the word anarthria. The majority of cases de- 
 scribed as motor aphasia are associated with impaired intelligence 
 and belong in the second variety of aphasia. 
 
 (2) Sensory Aphasia or Aphasia of Wernicke This form of 
 aphasia is associated with lesions in the supra-marginal and angular 
 gyri and posterior end of the second temporal convolutions. In this 
 condition there may be limited power of speech, but there is impair- 
 ment of intelligence and especially of the appreciation of spoken 
 words. There may also be loss of power to recognize written words 
 (alexia). The motor portion of this aphasia is due rather to the 
 individual's inability to understand his own spoken words. 
 
 (3) Anarthria In this condition there is a pure impairment 
 of the motor powers of expression. It is generally associated with 
 a lesion in the external capsule. Appreciation of speech written 
 and spoken is perfect and intelligence is unaltered. 
 
 Wernicke 's area must be regarded as only one of the great asso- 
 ciation centers of the brain between various forms of perception and 
 between them and motion. Lesions in them mean a blunting of 
 intelligence, because the power of forming complete concepts is 
 
 394 
 
THE NERVOUS SYSTEM 
 
 lacking though the individual may be in perfect possession of the 
 logical faculty. In true insanity there is an impairment of the 
 higher association centers located in the prefrontal region. The 
 simpler concepts are perfectly formed but the power of grouping 
 these in a manner necessary for the processes involved in logical 
 thought is lost. By means of the myelinization method Flechsig has 
 been able to divide up the cerebral cortex info some 36 areas. Eight 
 of these belong to the regions which have been described as asso- 
 ciated with the action end or primary projection areas of the cor- 
 tex. 
 
 In the case of seven areas the function is uncertain. The areas 
 do not possess either projection fibers or apparently association 
 fibers. 
 
 Eighteen areas are provided with short association fibers. They 
 may be termed intermediate areas. 
 
 Three areas possess long association fibers. They may be termed 
 the large and important association areas. One of these occupies 
 the prefrontal region on both the internal and external surface of 
 the cortex. A second occupies the 2nd and 3rd temporal convolu- 
 tions and the third a large area on the external surface of the cor- 
 tex, including the posterior portion of the supramarginal convolu- 
 tion and extending posteriorly to the visual perception area in the 
 cuneus. Until comparatively recently the nuclei of gray matter 
 grouped under the name of the corpus striatum and including the 
 lenticular nucleus and the caudate nucleus were regarded as simi- 
 lar in function to the optic thalamus and like it to constitute merely 
 relay stations for impulses on the way to and from the brain. 
 After destroying these nuclei, however, degenerated fibers are 
 found passing from them to the optic thalamus. These nuclei, 
 therefore, send out efferent fibers to lower cerebral nuclei. They 
 are also known to receive fibers from the optic thalamus and the 
 olfactory tracts. Such connections indicate that these nuclei 
 are independent masses of gray matter capable of receiving afferent 
 impulses from below and of sending out independent efferent im- 
 pulses. They must be regarded as relay stations within the brain 
 itself between the cortex and the lower thalamic centers. 
 
 In a series of animals representing an ascending scale of cere- 
 bral development the corpus striatum occupies a relatively less 
 importance in cerebral activities. In birds, on the other hand, they 
 
 396 
 
THE NERVOUS SYSTEM 
 
 have their greatest development. It would appear that they repre- 
 sent then a divergent development in birds, taking over an in- 
 creasing number of functions in them, while in mammals they are 
 retrogressive, their functions being shifted to the pallidium or 
 cerebral hemispheres. Stimulation of these nuclei produces no 
 
 Genu of corpus callosum. 
 Anterior horn of lateral 
 ventricle. 
 
 Caudate nucleus. 
 Anterior limb of internal 
 capsule. 
 
 Cavum septi pellucidi. 
 
 Genu of internal capsule. 
 
 Column of fornix. 
 
 Globus pallidus (of nucleus 
 
 lentiformis). 
 Fasciculus mammlllothala- 
 
 micus. 
 
 Posterior limb of Internal 
 capsule. 
 
 Thalamus. 
 
 Retrolenticular part of In- 
 ternal capsule. 
 
 Hippocampus. 
 
 Splenium. 
 
 Chorioid plexus. 
 
 Gyrus cingull. 
 Calcarine sulcus. 
 
 Lentlculo-caudate fibres. 
 
 U; Claustrum. 
 
 -Insula. 
 
 ^_ Putamen nucleus lentifor- 
 mis. 
 
 Internal capsule with ansa 
 lenticularis fibres in blue. 
 
 Tail of caudate nucleus. 
 
 Optic radiation. 
 Tapetum. 
 
 Optic radiation passing back 
 to white line in the area 
 striata. 
 
 Fig. 151. Horizontal section through the right cerebral hemisphere at the 
 level of the widest part of the lentiform nucleus. (Cunningham.) 
 
 movements. In the monkey their destruction is followed by no 
 definite results. In man lesions in these bodies produce tremors 
 in the execution of willed movements and an increased tonicity of 
 the muscles, functions resembling those of the cerebellum. 
 
 Experimental evidence of the nature of the application of iso- 
 lated heat and cold to the anterior part of the corpus striatum indi- 
 cates that this portion of gray matter contains the chief thermo- 
 
 398 
 
THE NERVOUS SYSTEM 
 
 * 
 
 taxic center of the body. Cooling it, for instance, produces shiver- 
 ing and increased heat production in the body, while warming it 
 produces the opposite effect. 
 
 The Histological Structure of the Cortex The preceding lo- 
 calization of nervous function within the cerebral cortex is largely 
 confirmed by a study of the histological structure of the cortex. The 
 cortex consists of many layers of cells imbedded in a neuroglia sup- 
 porting framework. As the 
 Purkinje cells are characteris- 
 tic of the cerebellum, so the 
 pyramidal cell belongs pecu- 
 liarly to the cerebral cortex. 
 It is a cone-shaped or 
 pear-shaped cell with one 
 large apical dendrite which 
 runs towards the surface to 
 break up in the most super- 
 ficial layers of the cortex into 
 number of branches. Den- 
 drites are given off from the 
 sides of "the cell. The axon 
 starts in the base of the cell 
 and passes down into the 
 white matter, giving off col- 
 laterals in its course. 
 
 Some fibers reach the cor- 
 pus callosum, others the in- 
 ternal capsule, and others ad- 
 jacent parts of the cortex. 
 
 There may be distin- 
 guished four or five layers of 
 cells within the cortex. (Fig. 
 152.) (1) Outer fiber lamina 
 or molecular layer contains 
 
 Fig. 152. Cerebral cortex, diagrammatic 
 section. 
 
 On the left, the cellular layers; on the f ^ spindle-shaped the 
 
 rnr circToma /-*T riKTocj" nn rno ovry^mo * A 
 
 right, systems of fibres; on the extreme 
 left a sensory fibre is seen ascending; 
 1, 2, 3, 4 the four layers of cells; 2 and 3 
 representing pyramidal cells of differing 
 size. 
 
 400 
 
 processes of which run paral- 
 
 lel to the sur f ace . The layer 
 
 . 
 
 is mostly composed of the 
 
 branching dendrites of the 
 
THE NERVOUS SYSTEM 
 
 cells of the deeper layers. (2) Outer cell lamina or pyramidal 
 cell layer. 
 
 It contains three varieties of pyramidal cells arranged from 
 without inwards into (a) small pyramidal cells, (b) medium pyra- 
 midal cells, (c) large pyramidal cells. (3) Stellate cell layer or 
 middle cell lamina, as indicated, contains stellate-shaped cells. (4) 
 Inner fiber lamina, composed of many nerve fibers and in certain 
 portions of the brain, particularly the motor areas, this layer con- 
 tains large solitary cells, the cells of Betz. (5) The polymorphous 
 cell layer and inner cell lamina, containing cells of many types, but 
 among which the pyramidal cells predominate. Some of the pyra- 
 midal cells are inverted, so to speak, their axons run to the surface. 
 These are called cells of Marinotti. Other cells, Golgi cells, possess 
 freely-branching axons ending near the cell. 
 
 The fibers from the white matter of the brain run toward the 
 surface, giving off a rich meshwork of fibers to the various layers 
 of gray matter. Other fibers run parallel to the surface and on the 
 very surface of the brain. These fibers in some regions, especially 
 the hippocampal region, are so well marked that they are termed 
 the tangential fibers. 
 
 Another layer of tangential fibers is found between the molecu- 
 lar layer and the pyramidal cell layer. It is called the outer line of 
 Baillance. 
 
 Internal to the granular layer is another layer of tangential 
 fibers, the inner line of Baillance. 
 
 In the occipital region there is a special tangential layer running 
 through the middle of the granular layer. It is called the line of 
 Gennari. 
 
 Identification of Function "by Means of Histological Detail 
 The thickness of these various layers furnish information as to the 
 function of the various portions of the cerebral cortex. 
 
 In the ascending frontal convolution the cells of Betz are numer- 
 ous and larger than in any other region. The pyramidal cell layer 
 is also very thick. 
 
 In the visuo-sensory area the stellate cell layer or granular layer 
 is thickest and the line of Gennari present. 
 
 In association areas, the parietal, temporal and frontal the outer 
 cell layer or pyramidal cell layer is very thick. It is the most 
 
 402 
 
THE NERVOUS SYSTEM 
 
 marked feature of sections in these regions. These cells, therefore, 
 have to do with the higher functions of association. 
 
 In animals lower than man, the ape and dog, less of the brain is 
 occupied with areas possessing the histological structure identified 
 with association. In still lower animals, the rabbit, the polymor- 
 phous layer is three times the thickness of the pyramidal layer. 
 
 We may, therefore, assign to the cells of Betz motor function, to 
 the pyramidal cells associative functions, and to the polymorphous 
 cells functions concerned in the getting of food and the gratification 
 of the various sensuous instincts. 
 
 When the cerebral activities are deficient either because of dis- 
 ease or congenital defects, the cells are less numerous in the regions 
 controlling the deficient functions. 
 
 Time of Certain Cerebral Activities The time of the various 
 reactions in which the brain is concerned is of interest. They may 
 be recorded by an electrical apparatus which marks the moment of 
 the application of any stimulus and, through a shunt circuit, the 
 voluntary reaction of the patient. 
 
 The time for the reaction to sight stimuli is .186 to .222 of a 
 second ; to hearing .115 to .182 second ; to electrical stimulation of 
 skin .117 to .201 second. 
 
 The time may be lengthened .006 second by fatigue of the reac- 
 tion, or by a dilemma, involving choice by the individual. 
 
 It may be shortened by practice, or by increase in strength of 
 the stimulus. 
 
 THE SYMPATHETIC NERVOUS SYSTEM 
 
 The nerves passing from the central nervous system to the vari- 
 ous portions of the body may be divided into two different classes. 
 First those conveying motor impulses from the spinal cord and 
 brain and those returning sensory impulses. In addition to these 
 nerves there is another class of nerves issuing with the cranial 
 nerves and the anterior and posterior roots of the spinal nerves 
 which convey afferent impulses from and efferent impulses to the 
 blood vessels and viscera. 
 
 Briefly, they supply smooth muscle and glandular tissue. 
 
 The nerves of this second class are connected with peripheral 
 
 404 
 
THE NERVOUS SYSTEM 
 
 ganglia and differ histologically from other nerves. All these facts 
 warrant their classification as a separate system. 
 
 It is called the vegetative nervous system, and may be divided 
 into the autonomic or cranial portion of the vegetative nervous 
 system and the spinal portion or the sympathetic nervous system. 
 
 In contradistinction from it we may call the other nerves of the 
 body those innervating skeletal muscle and returning sensory im- 
 pulses the somatic nervous system. 
 
 The vegetative nerves of the third cranial nerve pass with the 
 third nerve to the orbit. Leaving the branch of the third nerve 
 which supplies the inferior oblique muscle, they enter the lenticular 
 ganglion. From this ganglion their axons are continued, after inter- 
 ruption, as the short ciliary nerves to the sphincter pupili muscle 
 and the ciliary muscles. 
 
 The vegetative nerves of the 7th cranial nerve are contained in 
 the nerve of Wrisberg. This nerve also contains fibers of taste from 
 the tongue. The fibers belonging to the vegetative system, however, 
 leave the 7th nerve as the chorda tympani and later join the lingual 
 nerve and with this pass to the submaxillary ganglion. From this 
 ganglion it supplies dilator fibers and secretory fibers to the sub- 
 maxillary and sublingual salivary glands. The chorda tympani 
 also sends fibers to the sphenopalatine ganglion from which post- 
 ganglionic fibers supply the mucous membrane of the nose and soft 
 palate and upper part of the pharynx. 
 
 The vegetative fibers of the 9th nerve pass to the otic ganglion. 
 From this ganglion its post ganglionic fibers pass to the parotid 
 gland and supply it with vaso-dilator and secretory fibers. 
 
 Practically all of the vagus nerve may be regarded as belonging 
 to the visceral system. The jugular ganglion represents its ganglion 
 cell station. The ganglion of the trunk of the vagus probably cor- 
 responds to a posterior spinal ganglion and is connected with affer- 
 ent nerves of the vagus nerve only. As has already been mentioned, 
 it supplies motor fibers to the alimentary tract as far as the ileocolic 
 sphincter, inhibitory fibers to the heart, motor fibers to the bronchi 
 and secretory fibers to the stomach and pancreas. 
 
 Sympathetic Fibers of the Spinal Nerves Each spinal nerve 
 gives off fibers which participate in the formation of the visceral 
 system. They are represented in the anterior nerve roots by the 
 small medullated fibers. (Fig. 153.) These leave the anterior divi- 
 
 406 
 
THE NERVOUS SYSTEM 
 
 Fig. 153. Sections across parts of the roots of various nerves of the dog, to 
 
 show the variations in size of their constituent fibres. (Quain.) 
 (The nerves were stained with osmic acid, and the sections are all drawn 
 to one scale.) , 
 
 A, from one of the upper roots of the accessory. 
 
 B, a rootlet of the hypoglossal. 
 
 C, from the first cervical ventral root. 
 
 D, from the second thoracic ventral root. 
 
 sion of the spinal nerves and run to one set of ganglia but ter- 
 minate in one of two sets of ganglia. One of these sets of ganglia 
 forms a chain of ganglia lying close to the vertebral column. In 
 general there may be said to be one ganglion for each vertebral 
 segment of the column in the thoracic and lumbar region and three 
 ganglia for the cervical region. 
 
 The second series of ganglia are the cardiac plexus at the root 
 
 408 
 
THE NERVOUS SYSTEM 
 
 of the lung and base of the heart, the solar plexus around the celiac 
 axis, the superior and inferior mesenteric plexuses around the origin 
 of the superior and inferior mesenteric arteries, the hypogastric 
 and pelvic plexuses, in front of the body of the 5th lumbar vertebra. 
 We may call the spinal ganglia the lateral series of ganglia and 
 the ganglia in the large plexuses around the great vessels the col- 
 lateral ganglia. Another set of plexuses more distal still, exists in 
 the walls of the intestines. They are the plexuses of Meissner and 
 Auerbach. Though called terminal ganglia they contain no gan- 
 
 Spinal ganglion 
 
 Spinal 
 cord 
 
 Afferent fibre 
 } Efferent fibres 
 
 Sympathetic 
 efferent fibres 
 Sympathetic ganglion-flc* 
 
 i 
 
 Sympathetic afferent fibres 
 
 Fig. 154. Plan of construction of a typical spinal nerve. (Quain.) 
 
 glion cells and are rather to be viewed as sites of interlacing of 
 nerve fibers which suffer no interruption in passing through them. 
 All of the sympathetic nerves leaving the anterior division of the 
 spinal nerves pass to the spinal or lateral ganglia. As they are 
 medullated they are called white rami communicantes. Some of 
 them end in a terminal arborization around the cells of these gan- 
 glia ; others pass through these ganglia without interruption to end 
 around cells in the collateral series of ganglia. All these nerve 
 fibers are called preganglionic nerve fibers. From the cells around 
 which these preganglionic fibers end axons are given off which are 
 non-medullated and are called post-ganglionic fibers. (Figs. 154 
 and 155.) 
 
 No sympathetic nerve has more than one of these : iterruptions 
 
 410 
 
THE NERVOUS SYSTEM 
 
 between its origin and destination. Many of the axons of the cells 
 in the spinal ganglion run back from the ganglion to an anterior 
 spinal nerve, of a different level, bend around again to be distrib- 
 uted with the fibers of such an anterior or posterior spinal nerve. 
 
 As they pass, therefore, between the ganglia and the spinal 
 nerves they are also called rami communicantes, and because they 
 are not medullated they are called gray rami communicantes. 
 
 | Cells of 
 lat. horn 
 
 fost-ganglionic , 
 in spinal nerve 
 
 Spinal 
 cord 
 
 Pre-ganglionic fvbre 
 in sympathetic *"><> 
 
 Distal y. 
 in sympafr 
 
 fost-ganglionic fibre. 
 in; sympathetic 
 
 Post-ganqlionic fil>re_ 
 in spinal/ nerve 
 
 Fibre in sympathetic cord 
 gassing through two ganglia 
 
 Fig. 155. Diagram of sympathetic. (Quain.) 
 
 Each gray ramus communicans is distributed to only an area 
 of the body which corresponds to the level at which it is given off. 
 
 A white ramus, on the other hand, may run a long distance 
 before it terminates around a ganglionic cell from which its post- 
 ganglionic fiber is given off. Stimulation of one white ramus will 
 cause impulses in several gray rami. 
 
 412 
 
THE NERVOUS SYSTEM 
 
 The spinal ganglia of the upper three cervical nerves pass to 
 the superior cervical sympathetic ganglion. Its branches of distri- 
 bution are to plexuses around the carotid arteries and their 
 branches. 
 
 It sends branches to the tympanum and to the Vidian nerve and 
 to the Gasserian ganglion. Many fibers reach the superior cervical 
 ganglion from the first five dorsal nerves. These fibers reach it 
 after first passing through the dorsal spinal ganglia. They repre- 
 sent some of the white rami which have long preganglionic fibers, 
 for their ganglionic cells are in the superior cervical ganglion. 
 They convey the following impulses: 
 
 1. Vaso-constrictor impulses to blood vessels, 
 
 2. Dilator impulses to the pupil, 
 
 3. Secretory (trophic?) impulses to the salivary and sweat 
 glands, 
 
 4. Vaso-dilator fibers to the lower lip and pharynx. 
 
 The same five dorsal nerves send fibers to the stellate ganglion, 
 a large ganglion beneath the origin of the subclavian artery. It 
 communicates by two cords which surround the subclavian artery 
 with the inferior cervical ganglion of the sympathetic. The ring 
 around the subclavian is called the ansa Vienssens. The inferior 
 cervical ganglion of the sympathetic is placed between the superior 
 and middle cervical ganglion above, with which it is also connected 
 by two cords, and the stellate ganglion below. 
 
 From the cell stations of these fibers in the stellate ganglion 
 post- ganglionic fibers of the upper dorsal nerves are given off to 
 the heart. 
 
 They convey accelerator and augment or impulses to the heart. 
 
 Each spinal ganglion is not only connected with the anterior 
 spinal nerve by a gray and a white ramus but also with the ganglia 
 above arid below it by two connecting cords. 
 
 The upper limbs are supplied by nerves coming from the 4th to 
 the llth dorsal ganglia. 
 
 They convey : 
 
 1. Vaso-constrictor impulses to the blood vessels of the limbs, 
 
 2. Secretory fibers to the sweat glands. 
 
 The lower limbs are supplied by branches of the llth dorsal to 
 the third lumbar ganglion. 
 They convey : 
 
 414 
 
THE NERVOUS SYSTEM 
 
 1. Vaso-constrictor impulses to the vessels of the lower limb, 
 
 2. Secretory impulses to the sweat glands of the lower limb. 
 From the lower 6 dorsal and upper 3 to 4 lumbar ganglia fibers 
 
 pass to the abdominal viscera. 
 They convey : 
 
 1. Vaso-constrictor fibers to the vessels of the stomach and 
 small intestines, the kidney and spleen, 
 
 2. Probably vaso-dilator fibers as well, 
 
 3. Muscular inhibitory impulses to the stomach and small in- 
 testines, 
 
 4. Motor fibers for the ileocolic sphincter. 
 
 Nerves from the lower dorsal and upper 3 to 4 lumbar nerves 
 pass to the pelvic plexus in two strong cords running as the hypo- 
 gastric nerves from the inferior mesenteric plexus to the pelvic 
 plexus. 
 
 They convey : 
 
 1. Vaso-constrictor impulses to the vessels of the viscera, 
 
 2. Inhibitory impulses to the colon, 
 
 3. Both motor and inhibitory impulses to the bladder, 
 
 4. Motor fibers to the retractor penis, 
 
 5. Motor fibers to the uterus and vagina. 
 
 Besides the autonomic fibers passing in the hypogastric nerves 
 from the inferior mesenteric plexus to the pelvic plexus, the an- 
 terior branches of the second to the fourth sacral nerves furnish 
 branches of autonomic fibers which, without making connections 
 with any lateral ganglia, unite to form on each side the nervus 
 Erigens. This nerve passes directly to the pelvic plexus in which 
 its fibers suffer interruption. 
 
 They convey : 
 
 1. Motor impulses to the bladder, descending colon and rectum, 
 
 2. Vaso-motor impulses to the vessels of the pelvic viscera, 
 
 3. Inhibitory fibers to the sphincter of the bladder, 
 
 4. Dilator fibers to the vessels of the penis and inhibitory fibers 
 to the retractor penis. 
 
 416 
 
QUESTIONS AND ANSWERS 
 
 Pages 4-8 
 
 Q. What is the function which the nervous system has been developed to 
 perform? 
 
 A. To make possible the rapid transmission between distant portions of 
 the body of changes in the environment of groups of cells. 
 
 Q. What important stages in the development of a central nervous system 
 are represented by the nervous systems of invertebrates? 
 
 A. The peripherally placed nervous system of a hydra in which there is 
 but slight difference between the protective surface epithelial cell and 
 the specialized sensitive and conductive epithelial cell, and in which the sensi- 
 tive cell, the conductive portion and contractile tissue constitute one cell. 
 (Page 4.) 
 
 The peripherally placed nervous system of the jellyfish in which the 
 conductive tissue forms a ring about the periphery of the animal, separated 
 from the surface epithelium and contractive tissue but connected to both and 
 to different portions of itself by its own fiber like processes. (Page 8.) 
 
 The centrally placed nervous system of the worm, and of the still more 
 advanced crayfish: in both the cells of the conductive tissue are centrally 
 placed, thus facilitating communication between different portions of itself 
 and occupying the most efficient position for rapid communication with any 
 portion of the periphery. In the more advanced crayfish there is a special 
 development of the fore part of the central chain of nerve tissue, thus facili- 
 tating a quick appreciation of changes of the environment in the direction 
 in which the animal moves. (Page 12.} 
 
 Page 14 
 
 Q. How is the nervous system of mammals developed from the cells of 
 the embryo? 
 
 A. By the infolding of the epiblast, corresponding to the dorsum of 
 that group of cells of embryo from which all this tissue of the foetus are 
 developed, there is formed the neural canal, and on each side a depressed cord 
 of cells. By a differentiation of the cells lining the canal and forming the 
 cord the primitive spongioblasts and neuroblasts are formed. Both these 
 develop processes. The spongioblasts with their processes form the neuroglia 
 or supporting tissue of the nervous system. The neuroblasts of the neural 
 canal form nerve cells and their processes the motor nerves. These grow out 
 into the body of the embryo and form connections with every active tissue. 
 The neuroblasts of the lateral cords of cells develop into the nerve cells of the 
 sensory ganglia. They develop two processes, one forming peripheral connec- 
 tions with the various specialized sensitive cells of the body, and the other 
 growing centrally among the cells developing from the neural canal to partici- 
 pate in the formation of central synapses. 
 
 418 
 
THE NERVOUS SYSTEM 
 
 Page 34 
 
 Q. Describe a neuron. 
 
 A. A neuron consists of a nerve cell and its processes. A nerve cell pos- 
 sesses the following parts: See text. 
 
 A nerve has the following structure: See text. 
 
 Page 54 
 
 Q. Describe the different peripheral endings of nerves. 
 
 A. See text, and divide into sensory and motor nerve endings. 
 
 Page 
 
 Q. Classify nerves. 
 A. See text. 
 
 Page 74 
 
 Q. Describe the method of measuring the velocity of nerve impulses for 
 both motor and sensory nerves. 
 A. See text. 
 
 Q. In what direction does a nerve impulse travel? 
 A. In both directions from the stimulated point. 
 
 Page 76 
 
 Q. Is there any expenditure of energy caused by the passage of a nerve 
 impulse, how much and how is it estimated? 
 
 A. A very small amount, not enough to be indicated by its transformation 
 into heat, but only by the consumption of oxygen. 
 
 Page 78 
 
 Q. What is the demarcation current? 
 
 A. The current excited in a nerve by the degenerating changes following 
 injury to the nerve. 
 
 Q. What is the current of action? 
 
 A. The current which always accompanies the passage of a nerve impulse. 
 
 Q. In a muscle nerve preparation in what order do the tissues become 
 fatigued? 
 
 A. Motor end plate, muscle. The nerve is not known to become fatigued. 
 
 Page 84 
 
 Q. What is summation? 
 
 A. The reaction evoked by the combined effect of several sub-minimal 
 stimuli following each other at the proper favorable interval. 
 
 Q. What is the refractory period? 
 
 A. The period following an excitation during which the nerve remains 
 incapable of response to a second stimulus. 
 
 420 
 
THE NERVOUS SYSTEM 
 
 Page 86 
 
 Q. At what electrode does excitation of a nerve by an electrical current 
 take place? 
 
 A. At the cathode at the make, and anode at the break. 
 
 Q. What changes in degrees of excitability do these special sites of exci- 
 tation indicate and what names are made use of to express such changes? 
 
 A. They indicate changes in excitability which are proportional to the 
 response evoked, that change occurring at the cathode being named cathelec- 
 trotones, and at the anode, anelectrotones, so that the development of the one 
 and passing off of the other is what causes excitation. 
 
 Page 90 
 
 Q. How much of the nerve may be involved in anelectrotones or cath- 
 electrotones? 
 
 A. The greater the strength of the current the greater the length of the 
 nerve which is in anelectrotonus, the remainder of the nerve being in catelec- 
 trotonus. 
 
 Q. What effect do the facts expressed in the last answer have upon the 
 passage of the nerve impulse and what name is given to the phenomenon? 
 
 A. The nerve impulse may be blocked at the anode by a high degree of 
 anelectrotones or at the cathode by a swing back from a very high state of 
 cathelectrotones to a very low state of cathelectrotones. The phenomena 
 result in a response to stimulation which is different for different strengths 
 of the current used, and this fact is called Pfluger 's law. 
 
 Page 94 
 
 Q. What is the order of strength of contraction in the human being when 
 the electrode must be applied on the surface of the skin at a distance from 
 the nerve, and why is this order different from that order to be expected when 
 the electrodes are applied directly to the nerves according to Pfliiger 's law? 
 A. 1. See text for order. 
 
 2. Because there is a greater strength of current, due to convergence 
 of the lines of force between the electrodes, in that portion of 
 the nerve which is nearest to- the stimulating electrode. 
 
 Page 96 
 
 Q. What is the current of polarization and to what is it due? 
 
 A. The current of polarization is a current independent of vital changes 
 occurring in an electrically stimulated nerve, and is due to the difference in 
 potential which depends upon the collection of ions upon the electrodes and 
 bearing an opposite charge to the electrodes. These ions arise in the elec- 
 trolyte of the nerve sheath, and the phenomenon is common to any electrolyte 
 carrying a current. 
 
 Page 100 
 
 Q. What are the conditions affecting the excitatory effect in an electri- 
 cally stimulated nerve? 
 
 A. 1. The rate of change in the make or break. There is an optional 
 
 rate of change. 
 2. The intensity of the current. There is an optional intensity. 
 
 422 
 
THE NERVOUS SYSTEM 
 
 3. The duration of the current. There is an optional duration. This 
 
 duration is different for nerve, motor end plate and muscle. 
 
 4. The temperature. Warming the nerve of mammal increases its irri- 
 
 tability. 
 
 Page 104 
 
 Q. In what direction may an impulse pass across a motor end plate? 
 A. As is the case in all synapses, only in the normal direction. 
 
 Page 110 
 
 Q. Describe the gross anatomy of the spinal cord. 
 A. See text. 
 
 Page 116 
 
 Q. What are the groups of nerve cells in the gray matter? 
 A. 1. Anterior horn cells. The motor cells. 
 
 2. Small cells in the lateral portion of the base of the anterior horn, 
 
 the motor cells of the sympathetic nerves. 
 
 3. Cells in the lateral portion of the base of the posterior horn, 
 
 Clarke's column, the axons of which form the dorso-lateral cere- 
 bellar tract. 
 
 4. Cells of the posterior horn, many of which are receiving cells of 
 
 fibers of the posterior nerve roots, and others association cells. 
 
 Page 120 
 
 Q. What are some of the methods of tracing the systems of neurons? 
 A. The Myelination Method. See text for explanation. 
 The Wallerian Method. See text for explanation. 
 
 Page 126 
 
 Q. What is the termination of the fibers of the posterior nerve roots? 
 A. There are 5 sets of fibers: those forming 
 
 1. Lissauer's column. 
 
 2. The columns of Goll and Burdach. 
 
 3. The fibers ending in the cells of the posterior horn, from which 
 
 impulses are carried onward to the anterior lateral column of 
 the opposite side, to the anterior horn of same side, to posterior 
 horn of opposite side, to Clarke's columns of cells, to small 
 cells of lateral horn. 
 
 Page 136 
 
 Q. What are the descending spinal tracts? 
 A. See text. 
 
 Page 140 
 
 Q. What are the ascending spinal tracts? 
 A. See text. 
 
 Page 142 
 
 Q. What sensory impulses are carried by the various ascending tracts? 
 A. See text. 
 
 424 
 
THE NERVOUS SYSTEM 
 
 Page 144 
 
 Q. What are the symptoms of unilateral section of the spinal cord I 
 A. See text. 
 
 Q. How may the spinal functions be studied to the best advantage and 
 why! 
 
 A. By dividing the cord from the brain, because the functions of the 
 cord will thus be undisturbed by impulses from the brain. 
 
 Page 146 
 
 Q. What condition is induced by separation of the cord from the brain, 
 and what are the symptoms? 
 A. 1. Spinal shock. 
 
 2. Permanent loss of sensation and of voluntary motion below level 
 
 of lesion. 
 
 3. Temporary loss of muscular tone, of vascular tone and of reflex 
 
 response. 
 
 Q. To what are the symptoms of spinal shock due? 
 
 A. The permanent symptoms are due to division of the paths of sensory 
 perception and voluntary motor impulses. The temporary symptoms are due 
 to the division of paths through which, under normal conditions, impulses 
 responsible for both vascular and skeletal tone are constantly passing. These 
 paths include in part ascending tracts. 
 
 Page 150 
 
 Q. Define reflex action, explain its mechanism, and illustrate by spinal 
 reflexes. 
 
 A. A reflex action is any motor response produced by a sensory stimulus. 
 It involves an afferent limb, or sensory neuron, conveying the sensory stimulus 
 to the central nervous system, one or more central synapses, across which the 
 sensory stimulus is transmitted to the motor or efferent neuron. It is illus- 
 trated by the scratch reflex, sole reflex, vascular reflex, bladder and rectal 
 reflexes. The reflexes upon which muscular tone depends and tendon reflexes. 
 See text for description. 
 
 Page 156 
 
 Q. What are the characteristics of spinal reflexes? 
 A. Purpose like, etc. See text. 
 
 Page 178 
 
 Q. Define and describe a synapse and what is its function? 
 
 A. A synapse is the interval between the terminal arborizations of a 
 nerve fiber around the cell of another neuron with which it is functionally 
 related. This interval is not bridged by nerve fibrillse, so that there is no 
 direct continuation of nerve substance between one neuron and the next one 
 in functional association with it. The interval is filled with a granular 
 material which permits of the passage of nerve impulses in only one direction. 
 
 426 
 
THE NERVOUS SYSTEM 
 
 Page 176 
 
 Q. What is meant by the trophic functions of the spinal cord? 
 
 A. The spinal cord is constantly supplying to the peripheral tissues 
 through special nerve impulses, named trophic, which improve the nutrition 
 of these tissues. 
 
 Page 178 
 
 Q. How must the brain be considered phylogenetically and from what 
 embryological units does it develop? 
 
 A. As modified anterior segments of the primitive cerebro-spinal axis 
 or canal. The four divisions, into which the adult brain may be grossly 
 divided, develop from three primitive cerebral cavities at the anterior end of 
 the primitive neural tube. These three vesicles are named anterior, middle 
 and posterior cerebral vesicles. The anterior vesicle develops into the lateral 
 ventricles and cerebral cortex and third ventricles of the thalami. The middle 
 vesicle into the aqueduct of Sylvius and the brain stem with its nuclei. The 
 posterior vesicle into the fourth ventricle, the pons, cerebellum and bulb. 
 
 Page 180 
 
 Q. How are the retina of the eyes, the optic nerves, the olfactory bulbs 
 and olfactory nerves developed? 
 
 A. By tubular protrusions from the anterior cerebral vesicles. 
 
 Page 182 
 
 Q. Describe the floor of the fourth ventricle? 
 A. See text. 
 
 Page 186 
 
 Q. Describe the third brain. 
 
 A. See text. Mention iter of Sylvius and corpora quadrigemina and 
 geniculate bodies and their connections. 
 
 Q. Describe the third ventricle. 
 
 A. See text. Mention its shape, its roof, the corpus callosum and fornix, 
 its lateral walls, the optic thalami, its three commissures, and in the floor 
 the optic chiasma, the pituitary body and at its posterior corner the pineal 
 gland. 
 
 Page 192 
 
 Q. Describe the lateral ventricles. 
 
 A. See text. Mention the body and three horns. The roof is formed by 
 the corpus callosum; the floor of the body and roof of the inferior horn by the 
 optic thalami, the stria semicircularis and caudate nucleus with its tail, the 
 internal wall by the septum lucidum (anterior horn), the fornix and the choroid 
 plexus (body) ; and from above down, the forceps major and hippocampus 
 minor or calcar avis (the posterior horn), the choroid plexus and hippo- 
 campus major (inferior horn). The external wall of all horns and body by 
 the cerebral convolutions. The lateral ventricles communicate with the third 
 ventricles by the foramen of Monro, which opens into the anterior end of 
 the third ventricle beneath and behind the pillar of the fornix, from the 
 juncture of the anterior horn and body of the lateral ventricle. It is the 
 
 428 
 
THE NERVOUS SYSTEM 
 
 remnant of the neck of the bud from the primitive anterior cerebral vesicle, 
 the cavity of which forms the lateral ventricles and the eye walls. 
 
 Page 204 
 
 Q. Describe the cerebral hemispheres. 
 
 A. The cerebral hemispheres are divided into five lobes by four important 
 fissures. The fissure of Eolando (see text for position) separates the frontal 
 lobe on the external surface of brain from the parietal lobe. The fissure 
 of Sylvius (see text for position) forms the lower boundary of the frontal 
 lobe and parietal lobe on the external surface., separating them from the 
 temporal lobes. The parieto -occipital fissure (see text for position), which 
 separates the occipital lobe from the parietal and limbic lobes on the internal 
 surface of the hemispheres, and indicates the separation of the occipital from 
 the parietal and temporal lobes on the external surface of the hemispheres. 
 
 Page 234 
 
 Q. Describe the internal structure of the medulla. 
 
 A. The internal structure of the meHulla differs from that of the spinal 
 cord as a result of the opening out of the central canal of the cord into the 
 fourth ventricle of the bulb. The disposition of the gray matter represents 
 a displacement of the gray matter of the cord in a posterior and then a 
 lateral direction to a position lateral in the floor of the ventricle. In this 
 position it forms the nuclei of the cranial nerves in the positions described 
 and illustrated in the text. 
 
 A second difference between the internal structure of the medulla and 
 the cord is due to the passage of the fibers of the pyramidal tract from the 
 decussation on the front to the posterolateral position which they occupy in 
 the cord. In this passage they amputate and break up the gray matter of 
 the anterior horns, forming the lateral nucleus. 
 
 A third difference is due to the development of new gray matter, the 
 nucleus gracilis and cuneatus, in the posterolateral regions of the bulb in 
 which the columns of Goll and Burdach end. Another important mass of 
 gray matter appearing in the upper part of the bulb is the olivary nucleus. 
 On section it appears scalloped shaped, with its concavity directed toward the 
 center of the bulb. Its efferent fibers are afferent to the cortex of the cere- 
 bellum. 
 
 Page 258 
 
 Q. Describe the cerebellum. 
 
 A. The cerebellum is an isolated mass of brain tissue about 2%" x 1*4", 
 situated in the posterior fossa of the cranium and composed of two lateral 
 lobes and a central mass, forming a rounded intervening eminence above and 
 below. The surface of all these three lobes is thrown into convolutions and 
 contains immediately beneath it the gray matter of the cerebellum. The 
 tissue beneath this surface layer consists of white fibers which enter for 
 the most part the cerebellum in the three peduncles and pass to the cells in 
 the gray matter. Within the center of the cerebellum are four nuclei (see 
 text), which receive the efferent fibers from the gray matter of the cortex and 
 
 430 
 
THE NERVOUS SYSTEM 
 
 send efferent fibers from the cerebellum to the nuclei pontis and red nucleus. 
 While many fibers passing to the cerebellum probably make connections with 
 the deep nuclei, particularly those from the vestibular and Deiters' nuclei, 
 yet in general the afferent fibers to the cerebellum pass to the cortex and 
 the efferent fibers pass out from its deep nuclei. The afferent fibers to the 
 cerebellum pass to it through the three peduncles (see text, page 298). 
 
 Page 260 
 
 Q. Describe the third brain. 
 
 A. Above the pons the central canal of the cerebro-spinal system becomes 
 again a closed narrow canal, until it opens into the third ventricle. The 
 gray matter immediately surrounding it constitutes the nuclei of the oculo- 
 motor nerves. The superior peduncles of the cerebellum converge below the 
 canal to cross in a decussation and end in the cells of red nucleus, a large 
 mass of gray matter situated in the substance of the third brain below the 
 forepart of the aqueductus Sylvii. Above the forepart of the aqueduct, form- 
 ing rounded eminences on the dorsal surface of the third brain, are two 
 masses of gray matter on each side of the middle line, the superior and inferior 
 corpora quadrigemina. The superior corpora quadrigemina receive fibers from 
 the optic nerve and cerebellum. The inferior corpora quadrigemina receives 
 the lateral fillet and is related in function to the sense of hearing. 
 
 Page 262 
 
 Q. What is the posterior longitudinal bundle and its function? 
 
 A. A longitudinal bundle of nerve fibers is seen in all sections of the third 
 brain just ventral to the Sylvian aqueduct and is continued downwards through 
 the pons and medulla, being continuous with the tract of Marie or the 
 anterolateral association tracts of the spinal cord. By means of this tract 
 a connection is established between all the nuclei of the cranial nerve. See 
 Fig. 126. 
 
 Page 304 
 
 Q. Describe the subcortical masses of gray matter, and the external and 
 internal capsule. 
 
 A. The subcortical nuclei, apart from those belonging to the third brain, 
 are the claustrum, the lenticular nucleus, the caudate nucleus and the optic 
 thalami. 
 
 The claustrum is a thin mass of gray matter immediately underlying 
 the Island of Keil, being separated from it by a thin layer of white matter. 
 
 The lenticular nucleus, consisting of the putamen and the globus pallidus, 
 is a wedged shaped (on coronal section) mass of gray matter immediately 
 internal to the claustrum and separated from it by a thin layer of white 
 matter, the external capsule. 
 
 The caudate nucleus is a large mass of gray matter consisting of a 
 rounded anterior head and a long tail tapering out posteriorly, the whole 
 body being shaped somewhat like a long turnip or drawn-out pear. It 
 curves around the external periphery of the optic thalamus, forming the ex- 
 ternal part of the floor of the body of the lateral ventricle and the roof of 
 the external part of the inferior horn. It and the optic thalamus, which it, in 
 
 432 
 
THE NERVOUS SYSTEM 
 
 part, encircles, is separated from the lenticular nucleus by an important mass 
 of gray matter, the internal capsule. 
 
 The optic thalamus itself is a large mass of gray matter forming the 
 external wall of the third ventricle and the floor of the lateral ventricle and 
 bounded externally by the internal capsule and in part by the caudate nucleus. 
 
 Page SOS 
 
 Q. Describe the internal capsule, the pyramidal tracts and the cerebro- 
 pontine tracts. 
 
 A. The internal capsule is a thick stratum of white fibers passing in a 
 general vertical direction between the cerebral cortex and the pons. It is 
 flanked by the optic thalamus internally and the lenticular nucleus externally. 
 Its fibers pass to and from all parts of the cerebral cortex. Below they con- 
 stitute the crura cerebri, forming a great thick bundle on each side of the 
 middle line ventral to the third brain, and converging to plunge into the 
 upper part of the pons. See Figs. 100, 135. Through it run all the sensory 
 tracts from the optic thalami, continuing onward the mesial fillet to the 
 cerebral cortex; also within it pass the large motor tracts made of fibers 
 which are the axis cylinders of the cells of the motor area of the cortex. 
 These pass down through the central regions of the internal capsule and 
 crura cerebri to the pons. They plunge through the anterior portion of the 
 substance of the pons and appear on each side of the middle line of the 
 anterior surface of the medulla, where they constitute the two rounded emi- 
 nences known as the pyramids. Immediately below the pyramids they decus- 
 sate and pass downward in the lateral columns of the cord as the pyramidal 
 tracts, to terminate at various levels of the cord, either directly or indirectly 
 around the anterior horn cells. The internal capsule also contains fronto- 
 pontine and temporopontine fibers, passing from the frontal and temporal 
 lobes through the anterior and posterior limbs respectively of the internal 
 capsule and the mesial and external portions respectively of the crura to the 
 cells of the formatio reticularis. 
 
 Page SS6 
 
 Q. What are the portions of the olfactory mechanism in their physiological 
 order? 
 
 A. 1. The peripheral bipolar cells in the nasal mucosa. 
 
 2. The arborizing connection between the central process of these cells 
 
 and the peripheral processes of the mitral cells. 
 
 3. The mitral cells in the olfactory bulbs. 
 
 4. The olfactory tracts. 
 
 5. The portions of the brain and their connecting tracts which form 
 
 the olfactory mechanism. See text. 
 
 Page 340 
 
 Q. Describe the optic nerves? 
 
 A. The optic nerves are two large bundle of nerve fibers, these fibers 
 being axons of the ganglion cells in the anterior layers of the retinae, which pass 
 through the optic foramen to the optic groove on the upper surface of the 
 body of the sphenoid. In this groove the fibers from the inner half of each 
 
 434 
 
THE NERVOUS SYSTEM 
 
 retina decussate and pass them with the fibers from the external half of 
 each retina in two large bundles, the optic tracts, around the crura cerebri 
 (see Fig. 100) to the external geniculate body, the superior corpora quad- 
 rigemina and the posterior portion of the optic thalami. Axons of cells in 
 these nuclei then continue the visual sensations through the posterior portion 
 of the internal capsule, the optic radiations, to the occipital lobes. 
 
 Page SU 
 
 Q. What are the oculo-motor nerves and their function! 
 
 A. The oculo-motor nerves are the third, fourth and sixth. The nuclei 
 of origen of the third and fourth surround the Sylvian aqueduct. That of 
 the sixth is beneath the floor of the pontine portion of the medulla. They 
 supply oculo-motor impulses to the recti muscles of the eyeball the sixth 
 supplying the external rectus, the fourth the superior oblique and the third 
 the other muscles and sphincter pupili and ciliary muscle. 
 
 Q. What is the function of the fifth nerve? 
 A. See text. 
 
 Q. What is the function of the seventh nerve? 
 A. See text. 
 
 Page 346 
 
 Q. What is the function of the eighth nerve, and the central connections 
 of its fibers? 
 
 A. The eight nerve supplies to the central nervous system two sets of 
 impulses through the two separate portions of which it consists. 
 
 1. The vestibular portion is composed of axons of bipolar nerve cells 
 
 which have retained their original bipolar morphology, and the 
 peripheral processes of which end in the saccule, vestibule and 
 semicircular canals. It therefore transmits sensations of equilib- 
 rium. The central processes end in the vestibular nucleus be- 
 neath the mid-lateral portion of the floor of the fourth ven- 
 tricle. Its axons form important connections with Dieters' 
 and Bechterew's nuclei, two very important nuclei in the same 
 region. From these nuclei fibers pass to the roof nuclei and 
 cortex of the cerebellum. Doubtless some fibers of the vestibular 
 nucleus pass directly to the roof nuclei of the cerebellum. They 
 transmit impulses excited by changes in the position of the body 
 as a whole. 
 
 2. The auditory portion of the eighth nerve arises in the bipolar cells 
 
 situated in the crest of the cochlea. These also have retained 
 their embryonic bipolar morphology. Their peripheral processes 
 terminate in the auditory epithelium of the canal of Corti. 
 Their central processes end in the cells of the auditory tubercle 
 at the extreme mid-lateral angle of the floor of the medulla. 
 The impulses are carried across the middle line to the opposite 
 side of the medulla to form the ascending tract of the lateral 
 fillet by two sets of fibers, one superficial on the floor of the 
 medulla, the stria acoustica, and the other running directly to 
 the lateral fillet forming a decussation imbedded deeply in the 
 medulla and known as the trapezium. By means of the lateral 
 fillet the impulses pass to the internal geniculate body and the 
 
 436 
 
THE NERVOUS SYSTEM 
 
 inferior corpora quadrigemina, an'd thence through the internal 
 capsule and finally by the auditory radiations to the temporal 
 convolutions. 
 
 Page 350 
 
 Q. What is the function of the ninth, tenth and twelfth nerves? 
 A. See text. 
 
 Q. How may the functions of the brain be studied? 
 A. See text. 
 
 Page 352 
 
 Q. What are the afferent impulses received by the medulla? 
 A. See text. 
 
 Q. Describe the activities of the bulbo-spinal animal and how it differs 
 from the spinal animal. 
 
 A. Its cardiac, arterial and respiratory functions are normal. There is 
 a little greater stability of the spinal reflexes, due to the preservation of a 
 little greater degree of muscular tone. 
 
 Page 354 
 
 Q. Describe the activities of the pontine-bulbo-spinal animal. 
 
 A. It shows* all the reactions of the bulbo-spinal animal, but its position 
 and movements will preserve the normal position of its center of gravity. 
 There is greater increase in the stability of reflex movement. If such an 
 animal loses its cerebellum it becomes spontaneously active. 
 
 Q. Describe the activities of the midbrain-bulbo-spinal animal. 
 
 A. The mammal exhibits decerebrate rigidity (see text for definition) 
 and of course all the activities of which the pontine-bulbo-spinal animal is 
 capable. 
 
 The frog exhibits little that is abnormal in its deportment. 
 
 Page 356 
 
 Q. Describe the deportment of the thalamo-spinal animal. 
 
 A. Its deportment exhibits so little that is abnormal that only unusual 
 tests designed to bring into play activities which involve the exercise of 
 memory, and therefore choice, fear, affection, etc., are capable of detecting 
 anything abnormal. 
 
 Q. What are the functions of the cerebellum? 
 
 A. The cerebellum is the receiving station for the important nerves of 
 both proprioceptive and exteroceptive impulses of static sensation. The end- 
 ings of these nerves are so associated with association neurons of the cerebrum, 
 including the efferent control of the cerebrum over the spinal functions, 
 although there is probably some more direct efferent relation between the 
 efferent cerebellar impulses and the spinal functions through the vestibulo- 
 spinal tract, that there constantly leave the cerebellum a flow of efferent 
 impulses which provide for the most efficient co-ordination of individual muscles 
 during either states of rest or activity; and also, through chiefly the extero- 
 ception impulses of static sensation, the maintaining of the best balanced posi- 
 tion of the center of gravity of the whole body. 
 
 438 
 
THE NERVOUS SYSTEM 
 
 Page 860 
 
 Q. Describe the histology of the cerebellar cortex. 
 
 A. The characteristic cell of the cerebellum is the cell of Purkinje. It 
 is flask shaped and from its apex a rich turf of dendrites arise. Its axon 
 arises from the base of the cell and passes into the white substance of the 
 cerebellum to the central nuclei. This cell lies between two layers of smaller 
 cells, the dendrites and axons of which are chiefly associative in function. 
 
 Page 362 
 
 Q. What are the symptoms of the cerebellar less animal? 
 A. Asthenia, atonia and astasia. See text for definition. 
 
 Page 868 
 
 Q. What is the characteristic of cerebellar ataxia, and how does it differ 
 from the two types of spinal ataxia? 
 
 A. A failure to maintain the normal position of the center of gravity 
 of the body. It might be described as a top-heavy ataxia, exactly analogous 
 to the ataxia of a drunken individual. It differs from the spinal ataxia of 
 lateral sclerosis, in which the pyramidal tracts are degenerated, in that in 
 the latter all movements are exaggerated; the ataxia is due to over- movement. 
 It differs from spinal ataxia of tabes dorsalis, in which the posterior columns 
 of Goll and Burdach are degenerated, in that in tabes the ataxia is character- 
 ized by an inexactness of all movements depending upon a blunting of the 
 sensations inf ormatory of the exact position of individual muscles and tendons 
 and joints. 
 
 Page 370 
 
 Q. What additional possibilities of action does the possession of the cere- 
 bral hemispheres afford an animal? 
 
 A. That alteration of activity which depends upon memory. In the 
 animal deprived of its cerebral hemispheres the nervous path between the 
 incoming sensory impulses and action is so direct that these animals respond 
 to external stimulation with a machine-like certainty. 
 
 An animal with a cerebral hemisphere responds in an uncertain manner, 
 because of the influence of impulses along many association tracts which 
 have been brought into relation with incoming stimuli by past experiences. 
 In virtue of these intervening impulses between sensation and action a deport- 
 ment results which, according to the function of the action, is classified as an 
 expression of all the higher possibilities of which the mind is capable, such as 
 love, fear, self-restraint, etc. 
 
 Page 372 
 
 Q. What region of the cerebral cortex is the so to speak terminal dis- 
 charging station of motion? 
 A. See text. 
 
 Page 378 
 
 Q. What is the distinguishing characteristic of movements excited by 
 stimulation of the cerebral cortex? 
 
 A. Their similarity to the voluntary movements of the animal, involving 
 such a co-ordination of inhibition and contraction that the movement becomes 
 purposeful in the highest sense. 
 
 440 
 
THE NERVOUS SYSTEM 
 
 Page S80 
 
 Q. What is the difference in the character of the control exercised over 
 voluntary movement by the cerebrum and cerebellum? 
 
 A. The cerebrum initiates motion and determines what muscles shall be 
 called into play in the accomplishment of a definite movement or combinations 
 of motion, while the cerebellum controls the varying degree of contraction and 
 relaxation of muscles only so far as is necessary for the accomplishment of 
 perfect co-ordination and maintenance of the correct position of the center 
 of gravity of the body during the progression of these movements or the inter- 
 vening states of muscular contraction. 
 
 Page 384 
 
 Q. What area of the cortex is associated with the reception of sensations 
 of muscular sensations of touch, temperature and pain? 
 
 A. Tactile sensation of touch and muscular sensations are received first 
 by the cells of the ascending parietal convolution immediately posterior to 
 the fissure of Kolando, the inferior parietal and supramarginal convolutions. 
 
 Sensations of pain are received by cells fairly widely distributed in the 
 cortex. The location has not been exactly identified. Those cells receiving 
 the sensations of temperature have not been definitely located, but they prob- 
 ably occupy areas common to the cells receiving cutaneous sensibility. 
 
 Page 386 
 
 Q. What areas in the cortex receive visual sensations? 
 A. The cortex of the occipital lobes. 
 
 Page 388 
 
 Q. What area in the cortex receives auditory sensations? 
 
 A. The cortex of the superior temporal- convolution; but there is evidence 
 that this region is not the only one devoted to the reception of auditory 
 sensations, and that other more widely distributed areas also participate 
 in this function, though their exact location is as yet unidentified. 
 
 Q. What areas in the cortex receive sensations of smell and taste? 
 
 A. Many portions of the limbic lobe, including particularly the inferior 
 surface of the frontal lobe, the portion of limbic lobe contiguous to the corpus 
 callosum, the uncus and the hippocampus major. 
 
 Page 390 
 
 Q. What is the function of the large areas of the cortex intervening 
 between sensory and .motor areas described? 
 
 A. These so-called silent areas perform association functions. By them 
 the primary sensations are grouped into concepts, and the concepts themselves 
 are compounded and compared with other similar concepts, suggested because 
 of their analogy by them and the cerebral states depending upon this variety 
 of concepts, stimulated so that the rudiments of the higher faculties of choice 
 and judgment and decision are possible. These highest faculties are performed 
 by the frontal portions of the cortex. 
 
 442 
 
THE NERVOUS SYSTEM 
 
 Page S92 
 
 Q. How may words be psychologically defined, and how do they facilitate 
 cerebral processes? 
 
 A. Words are names given by the mind to concepts of varying complexity, 
 and by the use of these symbols for complex cerebral process, the cerebral 
 states involved in concepts of extreme complexity may be quickly produced, 
 and thus intricate thinking facilitated or made possible. 
 
 
 Page 394 
 
 Q. What is aphasia, how many kinds of aphasia are there, and to what 
 are they due? 
 
 A. Aphasia is an impairment in the power of speech. It may be an 
 anarthria, due to a pure inability to phonate. 
 
 It may be a motor aphasia, due to an inability to associate or select 
 the proper words to express properly formed concepts. 
 
 It may be sensory, due to the inability to associate with the name of a 
 concept its proper sound as heard or form as written. 
 
 Page 400 
 
 Q. Where is the thermotaxic center of the body situated? 
 A. Probably in the corpus striatum. See text. 
 
 Q. Describe the histology of the cerebral cortex? 
 
 A. The pyramidal shaped cell, with apical and lateral dendrites and basal 
 axon, is the typical cerebral cell. It is disposed in several layers composed 
 of pyramidal cells of different size, and is entirely associative in function. 
 In addition to these cells there are other layers of differently shaped cells, 
 superficial and deeper to them, and all layers are separated or crossed by 
 strata of fibers. The thickness of both layers of cells and of fibers differs 
 according to the functions of different portions of the cerebral cortex. 
 
 Page 406 
 
 Q. What is the vegetative nervous system, and into how many portions is 
 it divided? 
 
 A. In general that system the nerves of which supply the involuntary 
 muscles. It is divided into the cranial or autonomic, and the spinal or 
 sympathetic portions. 
 
 Q. What cranial nerves contain fibers of the vegetative nervous system, 
 and what do these nerves supply? 
 
 A. The third cranial, the vegetative nerves of which supply the sphincter 
 pupili and the ciliary muscle. 
 
 The seventh nerve, the vegetative nerves of which supply the sublingual 
 and submaxillary glands with secretory and vaso-dilator nerves to the parotid 
 gland. 
 
 The tenth is entirely vegetative. It supplies motor impulses to the 
 alimentary tract as far as the ileocolical valve, inhibitory impulses to the 
 heart, motor impulses to the bronchi, and secretory fibers to the stomach 
 and pancreas. It contains afferent fibers, passing to the important medullary 
 
 444 
 
THE NERVOUS SYSTEM 
 
 centers, and through which the heart beat is slowed and respiration is quick- 
 ened and the blood pressure lowered. 
 
 Q. Describe the anatomy and ganglia of the spinal sympathetic nerves. 
 A. See text. 
 
 Page 414 
 
 Q. What are the connections and functions of the superior cervical sym- 
 pathetic ganglia? 
 A. See text. 
 
 Q. What are the functions of the first five dorsal nerves making connec- 
 tions with the cervical and stellate ganglia? 
 A. See text. 
 
 Q. What sympathetic nerves supply the upper limbs and what are their 
 functions? 
 
 A. See text. 
 
 Q. What sympathetic nerves supply the lower limbs, and what is their 
 function? 
 
 A. See text 
 
 Q. What is the nerve supply of the pelvic plexus, and the function ful- 
 filled by them? 
 A. See text. 
 
 Q. What nerves form the nervi erigentes, and what is their function? 
 A. See text. 
 
 PAUL B. HOEBER, 67-69 EAST 59TH STREET, NEW YORK 
 
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