ORIGINS OF THE CEREBRAL CORTEX 69 



trailed ofFinto mysticism where science cannot follow. 

 Attempts to solve the problem objectively by analysis 

 of human and animal behavior have so far only raised 

 more new questions without answering the old ones, 

 though they have done great service in clearing the 

 ground of false or misleading preconceptions. Some- 

 thing may be gained by approaching the problem 

 from the other end, by reading the genetic history of 

 the cerebral cortex from the beginning instead of 

 trying to read human faculties backward into the 

 brutes. 



But where shall we begin? In the light of cerebral 

 organization of existing vertebrates and of the embry- 

 ological development of this organization we may 

 recognize four types of cortical structure. These 

 probably represent an approximation to the succes- 

 sive stages in the historical development of the cere- 

 bral cortex during the long evolution of the verte- 

 brate branch of the animal kingdom. These types 

 are: 



1. The ichthyopsid type. — Fishes and amphibians 

 have no well-differentiated cortex, though cortical 

 primordia are evident. That is, the regions within 

 which cerebral cortex appears in higher animals can 

 be identified and in some species. these regions exhibit 

 an approach toward cortical structure. 



2. The sauropsid type. — Reptiles and birds possess 

 clearly defined cortex, though limited in amount and 

 of very primitive structure. The subcortical parts of 



