THE EVOLUTION OF THE CEREBRAL HEMISPHERES. 



3T9 



150) and reptiles (Fig. 161), and ends in the homologue of the 

 recessus neuroporicus of fishes. This part of the median ventricle 

 has been called the recessus superior and in both reptiles and 

 monotremes its walls contain nervous elements and correspond to 

 the caudal part of the epistriatum in amphibia as explained above 

 (cf. Figs. 152 and 161). A transverse section through the com- 

 missures of a monotreme (Fig. 162) shows the general cortex 

 forming the lateral and dorsal wall of the lateral ventricles, while 



Fig. 160. — The mesial surface of the right cerebral hemisphere of a marsupial 

 (Phascolarctos). From G. Elliot Smith (Relation of Fornix, etc.). a, extra ventricular 

 alveus; d,d', fascia dentata; /, fimbria; g, neopallium; /,/', lamina terminalis;o, olfac- 

 tory bulb; o', olfactory peduncle; p, precommissural body; r, pyriform lobe; ^ 

 tuberculum olfactorium; v, ventral commissure (anterior commissure plus com- 

 missural fibers of the neopallium); w, hippocampal commissure; x, optic chiasma; 

 y, thalamus. 



the Strongly infolded mesial wall is the hippocampus. The 

 infolding is marked by a groove which appears on the mesial 

 surface of the hemisphere as the hippocampal fissure (Fig. 159). 

 The lower border of the hippocampus shows a higher special- 

 ization of structure and is known as the fascia dentata. The 

 lower wall of the brain is formed by the pyriform lobe and the 

 corpus striatum through which runs the large anterior commissure. 



