THE EVOLUTION OF THE CEREBRAL HEMISPHERES, 



315 



having larger hemispheres with a somewhat more complex struc- 

 ture in the olfactory cortex (Fig. 154), and in the position of the 

 hippocampal commissure. The olfactory lobe occupies the 

 anterior, lateral and ventral surfaces of the hemisphere, the base 

 is the corpus striatum and the dorsal and medial walls constitute 

 the hippocampus or olfactory cortex. The fiber tracts connect- 

 ing the olfactory lobe with the cortex and connecting both 

 with the hypothalamus and the nucleus habenulae seem to 

 be identical with those in amphibia. The tract from the dorso- 

 caudal pole to the hypothalamus is much larger than in amphibia. 

 Overlying the striatum in the ventro-lateral wall of the hemisphere 



Olfactory area 



Fig. 156. — A transverse section through the right lateral lobe of the forebrain of 

 Lacerta. After Cajal (Textura, etc.)- E, epistriatum; F, white substance of the 

 hippocampal formation; S, striatum. 



is a body called the epistriatum which represents the ventral, 

 unspecialized portion of the epistriatum in fishes. The anterior 

 commissure (Fig. 155) includes olfactory tract fibers, fibers from 

 the lateral olfactory area to the epistriatum, and fibers of the 

 tractus strio-thalamicus. The commissure of the hippocampal 

 region crosses in the upper part of the lamina terminahs and 

 passes in front of the foramen of Monro to reach the hippocampus. 

 The position of the commissure is the same as that of the hip- 

 pocampal commissure in monotremes and lower mammals. The 



