DISEASES OF THE NERVOUS SYSTEM. 



By M. R. Tbumbower, V. S. 

 [Revised by John R. Mohler, A. M., V. M. D.] 



ANATOMY AND PHYSIOLOGY OF THE BRAIN AND NERVOUS 



SYSTEM. 



(PI. XIX.) 



The nervous system may be regarded as consisting of two sets of 

 organs, peripheral and central, the function of one being to estab- 

 lish a communication between the centers and .the different parts 

 of the body, and that of the other to generate nervous force. The 

 whole may be arranged under two divisions : First, the cerebrospinal 

 system; second, the sympathetic or ganglionic system. Each is 

 possessed of its own central and peripheral organs. 



In the first, the center is made up of two portions — one large 

 and expanded (the brain) placed in the cranial cavity; the other 

 elongated (spinal cord), continuous with the brain, and lodged in 

 the canal of the vertebral column. The peripheral portion of this 

 system consists of the cerebrospinal nerves, which leave the axis 

 in symmetrical pairs and are distributed to the skin, the voluntary 

 muscles, and the organs. 



In the second, the central organ consists of a chain of ganglia, 

 connected by nerve cords, which extends on each side of the spine 

 from the head to the rump. The nerves of this system are dis- 

 tributed to the involuntary muscles, mucous membrane, viscera, and 

 blood vessels. 



The two systems have free intercommunication, ganglia being at 

 the junctions. 



Two substances, distinguishable by their color, namely, the white 

 or medullary and the gray or cortical substance, enter into the for- 

 n:ation of nervous matter. Both are soft, fragile, and easily injured, 

 ill consequence of which the principal nervous centers are well pro- 

 tected by bony coverings. The nervous substances present two dis- 

 tinct forms — nerve fibers and nerve cells. An aggregation of nerve 

 cells constitutes a nerve ganglion. 



The nerve fibers represent a conducting apparatus and serve to 

 place the central nervous organs in connection with peripheral end 

 organs. The nerve cells, however, besides transmitting impulses, 

 act as physiological centers for automatic, or reflex, movements, 

 and also for the sensory, perceptive, trophic, and secretory functions. 

 A nerve consists of a bundle of tubular fibers, held together by a 

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