71!) 



As usually studied, the nervous system is referred to in two main divisions: 



(1) The central nirroux xi/xt</n, composed of-(n) The spinal cord, or medulla 

 spinaiis. and (l>) t he brain or enceplialon. 



(L.M The /a ri/thi-nil m i-i'mix system, composed of (a) The cerebro-spinal nerves, 

 and (/>) the sympathetic nervous system. 



All those parts are so intimately connected with each other that the division is 

 purely arbitrary. The cerebro-spinal nerves are anatomically continuous with the 

 central system: their component fibres either arise within or terminate within the 

 confines of the central system, and thus actually contribute to its bulk. The sym- 

 pathetic system, however, may be more nearly considered as having a domain of its 

 own. It is intimately associated with the cerebro-spinal nerves and thus with the 

 central system, both receiving impulses from the central system and transmitting 



FIG. 555. SHOWING SO.MK OK TIIK VAHIETIES OF THE CELL-BODIES OF THE NEURONES OF THE 



HUMAN' XEKVOI-S SYSTEM. 



.1. From spinal ganglion. B. From ventral horn of- spinal cord. C. Pyramidal cell from cere- 

 bral cortex. D. Purkinje cell from cerebellar cortex. /.'. < lolgi cell of type II from spinal 

 cord. E. Fusiform cell from cerebral cortex. (7. Sympathetic, a, axone; d, dendrites; c, 

 collateral branches; ad, apical dendrites; bd, basal dendrites; cc, central process: ji, 

 peripheral process. 



impulses which enter it, but, while its activities are largely under the control of the 

 central system, it is possible that impulses may arise in the domain of the sym- 

 pathetic system and, mediated by its nerves, produce reactions in the tissues it sup- 

 plies without involving t he central system at all. For this reason, as well as because 

 of the structural peculiarities of the sympathetic system, the nervous system is 

 sometimes divided into (1) the cerebro-spinal system, consisting of (a) the central 

 system and (b) the eerebro-spinal nerves; (2) the sympathetic nervous system. 

 consisting of its various ganglia and plexuses. 



The nervous system consists of its peculiarly differentiated cell-elements, held 

 in place by two forms of supporting tissue and accompanied by an abundant supply 

 of blood-vessels. 



The nervous cell-element or the functional and structural unit of the sy stern is 

 called the neurone. The neurone is distinguished from all other units of structure 



