LACERTILIAAND CROCODILIA. 435 



Rocks of the United States, and the genus Dinophis has been 

 formed for, the reception of another gigantic constricting Ser- 

 pent from the same formation. In some of the later deposits 

 have been found the poisourfangs of a venomous snake. Upon 

 the whole, however, the snakes must be looked upon as a com- 

 paratively modern group, and not as one of any great geological 

 antiquity. 



CHAPTER LXIV. 



LACERTILIA AND CROCODILIA. 



Order III. Lacertilia. — The third order of Reptiles is that 

 of the Lacertilia, comprising all those animals which are com- 

 monly known as Lizards, together with some serpentiform ani- 

 mals such as the Blind-worms. The Lacertilia are distinguished 

 by the following characters : — 



As a general rule, there 1 are two pairs of well - developed 

 limbs, but there may be. only one pq.ir, or all the limbs may be 

 absent. A scapular arch is always present, whatever the con- 

 dition of the limbs may be. An exoskeleton, in the form of 

 horny scales like those of the Snakes, is almost always present. 

 The vertebrae of the dorsal region are procoelous or concave in 

 front, rarely ariiphiccelous or concave at both ends. There is 

 a single transverse process at each side, and the heads of the 

 ribs are simple and undivided. There is either no sacrum, or 

 the sacral vertebrae do not exceed two in number. The teeth 

 are not lodged in distinct < sockets. The eyes are generally 

 furnished with movable eyelids, and are always so in the com- 

 pletely snake-like forms. The heart consists of two auricles 

 and a ventricle, the latter partially divided by an incomplete 

 partition. There is a urinary bladder, and the aperture of the 

 cloaca is transverse. 



As a general rule, the animals included under this order 

 have four well-developed legs (fig. 169), and would therefore 

 be popularly called "Lizards." In some {Chirotes) there are 

 no hind-feet; in some {Bipes) the fore-limbs are wanting; and 

 others (Anguis, Pseudopus, and Amphisboend) are entirely des- 

 titute of limbs, thus coming closely to resemble the true Snakes 

 or Ophidians in external appearance. These serpentiform 

 Lizards, however, can be distinguished from the true Snakes; 

 ampngst other characters, by the structure of the jaws. In the 

 Snakes, as before said, the two rami of. the lower jaw are loosely 

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