CHAPTER XV 



THE NERVOUS SYSTEM 

 A. ITS ANATOMICAL BASIS 



In the preceding chapter we have repeatedly emphasized 

 the fact that sensations of all kinds are developed in the 

 brain from nervous 

 impulses coming 

 from the sense or- 

 gans, and in a pre- 

 vious chapter (VII) 

 we have seen that 

 Avithout reaching 

 the brain, or at 

 least without af- 

 fecting conscious- 

 ness, these affer- 

 ent impulses may 

 give rise to reflex 

 action. A reflex ac- 

 tion or a conscious 

 sensation, or both a 

 reflex action and 



FlG - 104 - Tne human brain viewed from above. 



The cerebral hemispheres completely cover the 



rest of the brain 



a conscous sensa- 



tion, may therefore 



-., j- ,1 



trance of a nervous 

 impulse into the central nervous system, and we have now 

 to inquire what is known of the mechanism by which these 

 results are brought about. 



263 



