THE NERVOUS SYSTEM 



gray commissure. Each crescentic mass has an anterior 

 and a posterior horn. The posterior horns are long and 

 narrow, and are connected with the posterior roots of the 

 spinal nerves. The anterior horns are shorter and thicker, 

 and are directed forward toward the anterior roots of the 

 nerves, but do not reach the surface. 



The spinal nerves will be subsequently considered. 



THE NERVES OF THE GENERAL SYSTEM 



We will now discuss the several nerves that control the 

 general system. Of these, the first to be considered are 

 the cranial. 



The Cranial Nerves. The first, or olfactory, is the 

 nerve of smell. It arises from the olfactory bulb and 

 terminates in the olfactory tract, which has three roots 

 inner, middle, and outer. The olfactory nerves, coming 

 from the olfactory bulb, are divisible into three groups: 

 the inner supplies the mucous membrane of the septum 

 of the nose; the middle supplies the roof of the nose; the 

 outer supplies the turbinated bones. The common sensi- 

 bility of the mucous membrane of the nose is derived from 

 the fifth nerve. 



The second, or optic, nerve is the nerve of sight. It 

 arises from the anterior pair of the corpora quadrigemina 

 and optic thalami. It rests on the sphenoid bone, then 

 passes through the optic foramen to terminate in the 

 retina. This nerve decussates at the middle of the com- 

 missure, a fact for which there seems to be no definite 

 reason. 



The third pair, or the motor oculi, apparently arises 

 from the inner surface of the crus cerebri, immediately in 

 front of the pons; it passes through the sphenoid fissure 

 and supplies all the muscles of the eye, except the superior 

 oblique and the external rectus. 



The fourth nerve, or pathetic, arises from the valve of 



