296 



THE NERVOUS SYSTEM 



from the cervical region of the column, twelve from the dorsal, 

 five from the lumbar, five from the sacral, and one from the 

 coccygeal. They are numbered according to their foramina of 

 exit. 



Each nerve rises by two roots an anterior which can be 

 traced to the anterior cornu of gray matter and a posterior 

 which goes (apparently) to the posterior cornu and these emerge 



B. 



FIG. 87. 



A. bipolar cell from spinal ganglion of a 4^ weeks' embryo (after His) . n, nucleus ; 

 the arrows indicate the direction in which the nerve processes grow, one to the spinal 

 cord, the other to the periphery. B, a cell from the spinal ganglion of the adult; the 

 two processes have coalesced to form a T-shaped junction. (Kirkes.) 



respectively from the antero-lateral and postero-lateral fissures of 

 the cord. Before leaving the spinal canal these two roots join to 

 pass through the corresponding ihtervertebral foramen as a single 

 tiunk which, however, just beyond that foramen divides into 

 anterior and posterior branches to be distributed to the anterior 

 and posterior parts of the body. 



The posterior root (inside the spinal canal) is sensory, and 

 has a ganglion developed upon it. The fibers of the posterior 



