GENERAL CHARACTERS OF REPTILES. 531 



face of the cerebrum is smooth, and without convolutions (Fig. 

 308). The two hemispheres (a) are oval, more or less 

 elongated, and hollowed out in the interior into a ven- 

 tricle, as in Birds ; there is no corpus striatum ; and 

 at their anterior part there are often observed olfactory 

 lobes of moderate size, situated at the origin of the first 

 pair of nerves. The optic lobes (b) are generally of 

 PIG 308 m derate s ^ ze 3 an< ^ are placed behind the hemispheres 

 on the same level. The Cerebellum (c) is, on the con- 

 trary, very small ; and (as in other oviparous Vertebrata) it does 

 not send beneath the Medulla Oblongata, that transverse pro- 

 longation or commissure, which aids in forming that ring around 

 it, which is possessed by Mammalia. The Spinal Cord (d) 9 

 compared with the brain, is very much developed ; and it may 

 also be remarked, that the nerves are larger in proportion to the 

 size of the central parts of the nervous system, than in the higher 

 animals. 



471. Most Reptiles have no special organ of touch ; and in 

 general this sense cannot be very much developed, on account 

 of the nature of their integuments. Some have, it is true, the 

 skin completely naked, and the epidermis scarcely distinct ; but, 

 in the greater number, it is covered by a thick epidermic layer 

 formed of plates more or less dense, consisting of horny or even 

 bony matter. The substance known under the name of Tortoise- 

 shell, and employed for such various uses, consists of the horny 

 plates which cover the carapace of a particular species of Turtle 

 (Fig. 328). Among Reptiles with a naked skin, the epider- 

 mis, being of slight consistency, is detached and renovated very 

 often ; and, among the animals of that class, in which it possesses 

 more consistency, it is also detached at different periods of the 

 year, to make room for a new epidermis. Sometimes this 

 species of moulting is partial, or, at least, the epidermis only falls 

 off by shreds ; but in other instances it is detached entire, and 

 preserves the form of the animal by which it is thrown off. 

 Serpents thus cast their skins several times a year. 



472. The eyes of Reptiles do not present anything very re- 

 markable ; their position is, in general, almost the same as in 



