THE NERVOUS SYSTEM OF MAN 1 53 



actions, but it has to depend on the other parts of 

 the nervous system for all of its information. It 

 is a mistake to suppose that with the formation of 

 this very large division of the nervous system, 

 new pathways and new relations were established 

 with the sense organs in either the spinal cord or 

 the "old-brain" as the brain of a fish or frog is 

 termed. The same general routes for the funda- 

 mental environmental responses persist and can 

 be identified in the brain and spinal cord of man. 

 Several old routes were abandoned when aquatic 

 animals became terrestrial and some new ones 

 occurred from time to time, but the great high- 

 ways remained. 



With the development of the cerebrum a 

 number of new connections were formed and 

 special secondary centers highly modified. Thus 

 there has grown up the modern conception that 

 man is largely dependent on his animal brain for 

 connection with his environment. Such a brief 

 epitome of the phylogenetic history of the central 

 nervous system reveals that man is deeply obli- 

 gated to his animal ancestry for his nervous 

 system. 



The ontogeny of the nervous system has been 

 presented in Chapter V and it is only necessary to 

 refer to the important fact that it is differentiated 

 from the same kind of cells as those which later 

 develop Into skin. But before this infolding 



