THE NERVOUS SYSTEM 



473 



made possible by the genesis of the central nervous systems of higher 

 animals from the nerve net of coelenterates. (Fig. 390) 



Dorsal root. 



Spinal nerve 



Cell of a 

 sympathetic 

 ganglion. Sympathetic 

 ramus. 



Spinal 

 ganglion. 



End disc 



Capstile. 



Fig. 391. — Diagram of the nervous elements in a human spinal ganglion. (From 

 Bremer's "Text Book of Histology.") 



In the primitive nerve plexuses of lower animals such as the coelen- 

 terates, and also in those of the vertebrate alimentary canal, the ganglion 



