460 MANUAL OF ZOOLOGY. 



earliest known traces of any serpent are in the Lower Kaino- 

 zoic Rocks, the oldest being the Palaepkis toliapicus of the 

 London Clay of Sheppey. The nearly-allied Palaophis typhaus 

 of the Eocene beds of Bracklesham appears to have been a 

 Boa-constrictor-like snake of about twenty feet in length. 

 Other species Q{ Palaophis have been described from the Tertiary 

 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 poison-fangs 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 

 animals, such as the Blind-worms. The Lacertilia are distin- 

 guished by the following characters : 



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

 limbs, but there may be only one pair, 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 amphicoelous 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 vertebras do not exceed two in number. The teeth 

 are not lodged in distinct sockets (some extinct forms con- 

 stituting an exception to this statement). The eyes are gene- 

 rally furnished with movable eyelids, and are always so in the 

 completely 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. 199), and would therefore 

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



