CLASS OF REPTILES. 321 



situated at the origin of the first pair of nerves. The optic 

 lobes are in general large, situated behind, and on the same 

 plane as the hemispheres ; but the little brain is small, and it 

 sends no prolongations across the medulla, so as to form a 



Fig. 281. Pterodactyle.* 



sort of ring, as in mammals. The spinal marrow, compared 

 to the brain, is large ; so also the nerves, as compared to the 

 cerebro-spinal axis, are larger than in the superior classes of 

 animals. 



462. The tactile sensibility is but little de- 

 veloped, the skin being generally protected by 

 horny scales : what we call tortoiseshell is merely 

 the horny plates covering the carapace of the turtle 

 (Fig. 277) , the testudo caretta. The epidermis is 

 frequently renewed, falling sometimes in portions or 

 plates, and sometimes cast off entire, as in serpents. 

 Serpents throw off the epidermic covering several Fig 282. 

 times a year. 



There is but little remarkable in the eyes of reptiles, but 

 upon the whole they resemble the eyes of birds ; a pecten 

 is but rarely found. Some have three eyelids, in others 



* The black part indicates the presumed contour of the skin. 

 Y 



