15G 



THE NERVOUS SYSTEM. 



FIG. 44. 



A, Cerebrum. 



B, Cerebellum. 



D, D. Spinal Cord. 



of them unites with a different 

 portion of the nerves which have 

 their origin in the spinal cord. 

 The importance of this part of 

 the nervous system is apparent 

 from the extreme care taken to 

 protect it from external injury. 

 For, while a very slight disturb- 

 ance of its structure suffices to 

 disarm it of its power, yet so 

 staunch is its bony enclosure, 

 that only by very severe injuries 

 is it put in peril. The three 

 membranes that cover the brain 

 are continued downward so as 

 to envelope and still further 

 shield this delicate organism. 



14. The Spinal Nerves. 

 The spinal- nerves, thirty- one 

 pairs in number, spring from 

 each side of the cord by two 

 roots, an anterior and a poste- 

 rior root, which have the same 

 functions as the columns bear- 

 ing similar names. The poste- 

 rior root is distinguished by pos- 

 sessing a ganglion of gray mat- 

 ter, and by a somewhat larger 

 size. The successive points of 

 departure, or the oif-shooting of 

 these nerves, occur at short and 

 nearly regular intervals along 

 the course of the spinal cord. 

 Soon after leaving these points, 



14. The spinal nerves? The posterior root? The nerves, how arranged: 

 "heir office ? 



