THE EVOLUTION OF THE CEREBRAL HEMISPHERES. 325 



commissure is due to the fact that it contains large numbers of 

 fibers connecting the lateral walls of the hemispheres. These 

 lateral walls together with the dorsal part of the mesial wall of the 

 hemisphere correspond to the similarly placed general cortex or 

 somatic palHum in man. This region has been called neopallium 

 to distinguish it from the olfactory cortex (archipallium) which 



Fig. 166. — Transverse section through the brain of the rat of four days at the 

 level of the anterior commissure. From Cajal (Textura, etc.). A, columna 

 fornicis; B, C and K tractusolfacto-hypothalamicus ("olfactory projection tract"); 

 D, lobus pyriformis; E, nucleus lentiformis of corpus striatum; F, tractus opticus; 

 H, anterior commissure; J, cingulum; R, nucleus caudatus of corpus striatum; 

 T, fasciculus longitudinalis superior. 



is traceable continuously from selachian fishes to mammals. 

 The neopallium has developed in the lateral and dorsal wall of 

 the hemispheres, crowding between the mesial and lateral parts 

 of the olfactory lobe and pushing the lateral part down upon 

 the ventral surface. The commissural fibers of this neopalHum 



