riS 



VEllTEmi ATE AXI.MA I.S. 



The class HrptiUu includes, aiuoiig living forms, the Tortoises and 

 Turtles {('lidiiiilii), tlie Snakes (O/ihiilid), the Lizards {Lacertilia), 

 and the (.'rociidiles {(_'rin-i>iUliii). Witli the exception of the Tor- 

 toises anil Turtles, tliey are mostly of an elongated cylindrical form, 

 furnished behind with a long tail. The limbs may be altogether 

 alisent or quite rudimentary, as in the Snakes, but in alniost all the 

 higher members of the class there are two pairs of limbs, which may 

 be eitlier adapted for walking or swinnning, and wdiich in some 

 extinct foi-ms support a flying membrane. The internal skeleton is 

 always liony, never cartilaginous or scnn-cartilaginous as in many of 

 the H<l[cs. The skull is joint^'d to the spine by a single articulating 

 surface (or fnntljilr). The lowci' j iw is com])lex, each half being 

 composed of several ]iieccs \uiited by sutures. In Tortoi.ses and 

 Turtles, hiiwever, these separate jiieces are ama.lg.-imated together, 

 and the two halves are also united, so that the whole lower jaw 

 appears to form .a sin^'le piece. In most reptiles, on the other hand, 

 the two halves of the lower jaw (Hg. 18.")), are only loosely united ; 

 in the Snakes by ligaments .-ind muscles, in the Lizards by gristle, 

 and in the Crocodiles Iiy sutui-e. In all, the lower jaw is jointed 





Fi-. IS-,.— Skull nCa Si'ipciit (PyllKMiy n Qimtlr.ite l.rmf ; /. Luwi-v j nv, 

 ;n-liciil,'itii)- ivith I he innv;ilil,' (luuilrate linni' {u). 



to the skidl )iy means of ,-i, speci.al l.ione, called the " ([uadrate 

 bone"; .and .as this often jirojects backwards, the o]ieiiing of the 

 mouth is often very extensive, and may even extend backwa'rils 

 beyond the b.'isc of the .skull (Hg. bs.'i, n). Teeth are generally jires- 

 ent, but these ;ire useil chicHy to hold the lircy, ami not in biting or 

 chewing the food. K.\ce|it in the ( 'I'ocodiles, the teeth .are not sunk 

 into distinct sockets, and they .-ire usii.ally repl.-u'ed as fast as shed. 

 They likewise do not dili'er fiiim one another siitliciently in form or 

 function .-IS to allow (jf their being divided into ditlerent .sets, as they 

 (,111 b(, ill llii< M,iinm:ds. Usually the teeth are conhned to the jaws 



