PROBLEM OF THE CEREBRAL CORTEX 31 



muscular tone. It is highly developed in all active 

 animals from fishes to men; and, although much 

 larger in higher forms, it is not otherwise greatly 

 modified in internal structure or mode of action. 

 The stimuli by which it is activated arise for the most 

 part within the body, and its activities are wholly 

 unconscious. 



The cerebral cortex, as we shall see, in a somewhat 

 similar way has emerged from reflex centers of the 

 forebrain which are activated chiefly in response to 

 what is going on outside the body — the exteroceptive 

 apparatus. In the early stages of its development it 

 seems to serve, like the cerebellar cortex, chiefly as 

 an activator, reinforcing, inhibiting, or otherwise 

 modifying and controlling the innate reflex patterns 

 of the lower centers out of which it has grown. 



The cortex of both the cerebellum and the cere- 

 brum exerts a dynamogenic influence upon lower 

 correlation centers, the patterns of whose activities 

 are established subcortically in these more primitive 

 reflex centers. That is, what the animal will do in 

 response to a relatively simple situation is determined 

 by adjustments made in the correlation centers of the 

 brain stem. The cerebellar and cerebral cortex are 

 knit into these lower centers iii such a way as to 

 facilitate a reaction whose basic physiological charac- 

 ter or behavioristic motive has already been elsewhere 

 determined. 



So far there is a parallelism between these two 



