THE EVOLUTION OF THE CEREBRAL HEMISPHERES. 313 



parts of the hemisphere are at least chiefly tertiary. The internal 

 structure of this region is more complex than in fishes. In addition 

 to the pyramidal cells characteristic of the epistriatum of fishes 

 there are many cells of type II and tangential cells present. It is 

 clearly evident that this region constitutes an olfactory cortex 



Fig. 154. — Part of a transverse section of the cortex of a chameleon. After 

 Cajal (Textura, etc.). A, superficial plexiform layer; B, layer of pyramids; C,deep 

 plexiform layer; D, white substance; E, ependyma. 



and corresponds to the hippocampal formation in the mammalian 

 brain. The commissure of this region must therefore be compared 

 functionally with the hippocampal commissure. Anatomically, 

 however, the commissure in amphibia is not the same as that in 

 mammals. The upper commissure in amphibia lies beneath the 

 median ventricle and behind the foramen of Monro and could not 



