PROBLEM OF THE CEREBRAL CORTEX 37 



the implicit or internal behavior is elaborated and 

 absorbs more of the total process. 



This glimpse of the general characteristics and 

 evolutionary history of the cortex makes it evident 

 that no single anatomical or physiological feature will 

 be found which alone can serve to define the cere- 

 bral cortex. It is possible, however, to assemble the 

 physiological factors which seem to have conditioned 

 the evolution of these master-tissues. In the following 

 chapters an outline of cortical origins will be sketched 

 in the hope of clarifying the part played by the 

 cerebral cortex in vertebrate evolution, the early 

 steps in its fabrication, and the physiological in- 

 fluences involved. 



