LACERTILIA, 361 



or Mesozoic deposit. The earliest known traces of any ser- 

 pent are in the Lower Kainozoic Rocks, the oldest being the 

 Palceophis toliapicus of the London Clay of Sheppey. The 

 nearly-allied Palaophis typhaus of the Eocene beds of Brackle- 

 sham appears to have been a Boa-constrictor-like snake of 

 about twenty feet in length. Other species of Palceophis 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 Serpent 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 comparatively modern group, 

 and not as one of any great geological antiquity. 



ORDER III. LACERTILIA. The third order of Reptiles is 

 that of the Lacertilia, comprising all those animals which are 

 commonly known as Lizards, together with some serpentiform 

 animals such as the Blind-worms. The Lacertilia are dis- 

 tinguished 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 amphiccelous 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, and would therefore be popu- 

 larly called " Lizards." In some (Chirotes) there are no hind- 

 feet ; in some (Bipes) the fore-limbs are wanting ; and others 

 (Anguis, Pseudopus, and Amphisbczna) are entirely destitute 

 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, 

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

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

 loosely united in front by ligaments and muscles, and are 



