422 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



In the Amniota we find considerable advances 

 in the characters of the brain, which are chiefly due 

 to the angulation of its several parts, and the thicken- 

 ing undergone by the walls of the primary vesicles at 

 various points. 



In the Reptilia the cerebral hemispheres are 

 always smooth on their surface, but they are now, and 



Fig. 181. Side views of the Brain of a Tortoise (A) and a Bird (B). 



I, Olfactory nerves; \.ol, olfactory lobes; VFT, cerebral hemispheres; n, optic 

 nerves ; Tro, optic tract ; inf, infundibuluin ; H, hypophysis cerebri ; T, 

 temporal lobe; MH, optic lobes; HH, cerebellum; NH, medulla oblougata ; 

 R, spinal cord. (After Wiedersheim.) 



henceforward, always large in proportion to the re- 

 maining parts of the brain ; the hemisphere of either 

 side is united to its fellow by a transverse band of 

 fibres (commissure), which lies just in front of 

 the third ventricle ; the optic thalami are similarly 

 united by a transverse commissure j the cerebellum 



