302 THE ANATOMY OF VERTEBEATED ANIMALS. 



Fin;. 90. 



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Fig. 90. — A, C, the brain of a Lizard (^Psainmosnurus bengalensW), and 

 B, D, of a bird (Meleapris gallopavo, the Turkey), drawn as if they 

 ■were of equal lengths. A, B, viewed from above : C, D, from the left 

 side. Oif., Olfactory lobes ; Pn., Pineal gland ; Hmp., cerebral 

 hemispheres ; Mb., optic lobes of the mid-brain ; Cb., cerebellum ; 

 31. O., medulla oblongata ; ii., iv., vi., second, fourth, and sixth pairs 

 of cerebral nerves ; Py., pituitary body. 



The brain (Fig. 90) fills the cavity of the skull iti the 

 ^agherSauropsida, and presents a well-developed cerebeUum; 

 a mesencephalon divided above into two optic lobes; and 

 relatively large prosencephalic hemispheres, which attain a 

 considerable size in Crocodilia and Aves, but never conceal 

 the optic lobes. In Crocodilia the cerebeUum presents a 

 distinct vermis, with transverse fissures. In birds the 

 latter are more distinct, and the lateral appendages o£ the 

 cerebellum, or flocculi, become well defined, and are lodged, 

 as in many of the lower Mammalia, in cavities of the side 

 walls of the skvill, arched over by the anterior vertical 

 semicircular canal. 



There is no pons Varolii, in the sense of transverse fibres 

 connecting the two halves of the cerebellum, visible upon 

 the ventral surface of the mesencephalon. The optic lobes 

 contain ventricles. In Reptilia, the optic lobes usually lie 

 close together upon the dorsal side of the mesencephalon. 



