DISEASES OF THE NERVOUS SYSTEM. 



By M. R. Tbumbowee, V. S. 

 [Revised In 1903 by Leonard Pearson, B. S., V. M. D.] 



THE ANATOMY AND PHYSIOLOGY OF THE BRAIN AND NERVOUS SYSTEM. 



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

 organs, peripheral and central, the function of one being to establish 

 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 elon- 

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

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

 tem consists of the cerebro-spinal 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 con- 

 nected by nerve cords which extends from the head to the rump on 

 each side of the spine. The nerves of this system are distributed 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, enter into the forma- 

 tion of nervous matter, namely, the white or medullary, and the gray 

 or cortical substance. Both are soft, fragile, and easily injured, in 

 consequence of which the principal nervous centers are well protected 

 by bony coverings. The nervous substances present two distinct 

 forms— nerve fibers and nerve cells. An aggregation of nerve eel Is 

 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 



190 



