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 

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

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

 moderate size ; and are placed behind the hemispheres 

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

 trary, very small ; and (as in other oviparous Yertebrata) 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 (c?), 

 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, from the na- 

 ture of their integuments, the skin being covered by a thick epi- 

 dermic 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, con- 

 sists of the horny plates which cover the carapace of a particular 

 species of Turtle (Fig. 318) ; and the majority of the Tortoises 

 and Turtles are in like manner coated with horny matter. The 

 epidermis is detached at different periods of the year, to make 

 room for a new formation. 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. In the latter case the skin 

 when shed presents a perfect cast of the outer surface of the ani- 

 mal, every mark and line upon the scales being exactly reproduced, 

 whilst in the snakes, even the transparent skin which covers the 

 eyes is shed. Serpents thus cast their skins at least once a year 



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

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



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