PROBLEM OF THE CEREBRAL CORTEX 29 



of behavior, including its part in physiological and 

 psychological choice, associative memory, voluntary 

 effort, and purposive action. 



When the whole evidence is reviewed, we find that 

 there is no single anatomical criterion by which 

 cerebral cortex can be distinguished from other sheets 

 of superficial gray matter in the cerebral hemisphere 

 (as the "cortex" of the anterior perforated substance), 

 and in some places cortex passes over into obviously 

 subcortical gray centers by insensible gradations. 

 Though the search for intrinsic anatomical features 

 which specifically characterize cerebral cortex is vain, 

 if we direct our attention to the types of intrinsic 

 and extrinsic connections made by its neurons and 

 to the physiological features related with these pat- 

 terns of interneural connection, the specific features 

 of this cortex (or some of them) come to light. 



A comparison of the cortex of the cerebrum with 

 that of the cerebellum is instructive in this connec- 

 tion. In a recent review of the evolutionary history 

 of the cerebellum (1924^) I have called attention to 

 the fact that in the simplest vertebrates the vestibular 

 centers of the medulla oblongata are the cradle of the 

 cerebellum. This is a strictly reflex mechanism of ad- 

 justment of equilibration and muscular tone, acting 

 primarily under the influence of the semicircular 

 canals of the internal ear. In the more active animals 

 with greater diversification of bodily movements the 

 cerebral center of this system enlarges and into it are 



