SUMMARY OF CORTICAL EVOLUTION 257 



of any one sensory system of afferent fibers and pro- 

 moted by physiological diversity of the afferent fibers. 



2. This cortex does not appear until (in reptiles) 

 the underlying reflex centers of the cerebral hemi- 

 spheres (septal and strio-amygdaloid complexes) are 

 greatly enlarged and complicated. The dorsomedial 

 (hippocampal) cortical sheet is intimately related 

 with the medial olfactory area and septum; the dorso- 

 lateral (pyriform) sheet is intimately related with the 

 lateral olfactory area; the dorsal sheet (general cortex 

 or neopallium) is intimately related with the non- 

 olfactory part of the corpus striatum, but is primi- 

 tively more detached from lower reflex centers than 

 are the other two cortical sheets. The underlying 

 basal or subcortical centers related, respectively, with 

 the three cortical sheets perform very diverse func- 

 tions of reflex correlation. The resulting physiological 

 diversity of the overlying cortical sheets is a pre- 

 requisite for the performance of associations of corti- 

 cal type. 



3. The specific intrinsic functions of the cortex 

 comprise intracortical correlations between these di- 

 verse cortical areas. These functions are superposed 

 upon those of the subcortical reflex centers, though 

 intimately knit in with them. The cortex is not acti- 

 vated except through the lower reflex centers, and 

 primitively it acts synchronously with them. 



4. Cerebral centers within which cortex is differ- 

 entiated are more or less detached in space and physi- 



