CHAPTER IX. 



THE BRAIN OF REPTILES AND OF BIRDS. 



The nervous system of Reptiles generally exists in a 

 slightly more developed form than that which is common 

 amongst Fishes. 



The Spinal Cord occupies the whole length of the 

 spinal canal. It is slender and almost uniform in thick- 

 ness in Serpents, though it is relatively stouter in Croco- 

 diles and their allies. In the latter it also presents 

 decided swellings in those regions whence the nerves are 

 given off, on each side, for the fore and hind limbs. 



The principal divisions of the Brain are the same in all 

 kinds of Reptiles, though, as might have been expected from 

 the varied form and nature of the different representatives 

 of this great class, the respective development of the 

 several divisions of the organ varies much in different 

 orders. 



The Medulla Oblongata, directly continuous with the 

 spinal cord, slightly widens at its upper part, where it is 

 surmounted by the Cerebellum. This latter structure, in 

 the Lizard (fig. 59) and its allies, is very small, consisting 

 only of a thin lamella. The cerebellum is larger, how- 

 ever, among Serpents (fig. 58), and it becomes still more 

 developed in Turtles (fig. 61) and Crocodiles. 



The Optic Lobes are relatively smaller in most Reptiles 

 than they are among Fishes ; and in the Boa Constrictor 



