220 COMPARATIVE ANATOMY 



infundibulum and hypophysis extend far backwards : details 

 regarding the pineal apparatus are not known. 



Reptiles. The brain of Reptiles reaches a considerably higher 

 stage of development than that of the forms already described, 

 and the individual parts overlie one another to a greater extent, 

 especially in the Agamse and Ascalabotse. 



In the brain of Dipnoi and Amphibia there are comparatively 

 few cellular elements in the outer layer of the pallium, and the 

 larger masses of cells (central gray matter) line the ventricles : 

 in the Reptilia a peripheral shifting takes place, giving rise to the 



Parietal organ _ ^ SS^^J^L _ External and internal 



layer oj optic cup 



Nerve 



Epithelial roof of ^C^^L^N \MW -%&-. P"wd organ (epiphytis) 

 3rd ventricle 



Superior commissure _ _ _ 



FIG. 168. SKETCH OF THE PINEAL APPARATUS OF HATTERIA. (After Dendy.) 



formation of a definite cortex, containing the characteristic pyra- 

 midal cells such as are present in all the higher Vertebrates. It 

 appears that the first differentiation of a cortex phylogenetically 

 was connected with the olfactory sense : while in Fishes, for 

 example, the olfactory tracts terminate in the corpora striata, most 

 of their fibres extend into a definite region of the pallium from 

 Reptiles onwards. Thus an " olfactory cortex " is formed, to which 

 other centres are gradually added in the ascending series of 

 Vertebrates. 



The pallial commissures (Fig. 165), like those of Amphibians, 

 are not large relatively, but in addition to an anterior pallial or 

 hippocampal commissure, traces are present of a so-called "fomiix " 

 (posterior pallial commissure, p. 201); the hippocampal lobes 



