ORIGINS OF THE CEREBRAL CORTEX 91 



field). This area is roughly comparable with the 

 area parietalis of the opossum (Fig. 14). Comparison 

 of the relative thickness of the layers in these two 

 sections brings out vividly the greater development 

 of the human supragranular cortex (layers II and III 

 of Brodmann). This is a point of great importance 

 in view of Bolton's (19 14) belief that these layers con- 

 tain the nervous mechanisms chiefly concerned with 

 the higher individually learned cortical functions. 



Figure 17 illustrates two forms of neurons which 

 are especially characteristic of neopallial cortex. At 

 the left is a pyramidal cell whose axon enters the 

 underlying white matter and may connect with very 

 remote parts of the cortex. At the right is a cell (type 

 II of Golgi) whose short axon breaks up in the imme- 

 diate vicinity of the cell body (p. 317). 



The organization of the cerebral hemispheres of 

 reptiles, birds, and mammals makes it plain that the 

 cerebral cortex is related genetically and physiologi- 

 cally with the corpus striatum complex in very inti- 

 mate fashion and that this relationship changes 

 radically between the sauropsid and the mammalian 

 types. It is impossible in the present state of our 

 knowledge to treat this subject adequately, but its 

 importance in the problem of cortical functions is so 

 great that some attention must be paid to it before 

 we can advance further. 



