VERTEBRATA : REPTILIA. 547 



Lizards in external configuration, whatever their exact nature 

 may be and from this point of view it is often very useful as 

 applied to many fossil forms, the structure of which is only 

 imperfectly known. It is therefore perhaps best to employ 

 this term merely in a loose general sense. All the Lacertilians 

 possess teeth, though these vary considerably in their arrange- 

 ment. (If the extinct Rhynchosaurus be truly Lacertilian, this 

 genus has apparently no teeth.) The teeth are always simple, 

 sometimes sharp and conical (Monitor), sometimes blade-like 

 with serrated edges (Iguana), sometimes with rounded crush- 

 ing crowns (Cydodus). Usually the teeth become anchylosed 

 to the jaw, when they may be fixed by their sides to the inner 

 wall of the alveolar border of the jaw ("pleurodont" den- 

 tition), or may be attached by their bases to the summit of 

 this border (" acrodont " dentition). In the extinct Protoro- 

 sauria, the teeth are implanted in distinct sockets (" theco- 

 dont" dentition). 



The Lacertilia are sometimes divided into three sections in 

 accordance with the structure of the tongue. In one group, 

 including the greater number of the members of the order, 

 the tongue is long, protrusible, and forked (Fissilinguia or 

 Leptoglossci), as in the Serpents. In a second group (Brevi- 

 linguia or Pachyglossa), including the Geckos and Agamids, 

 the tongue is thick, fleshy, and not protrusible. Lastly, in a 

 third group ( Vermilinguia] are placed the Chameleons, with 

 their long protrusible worm-like tongue, the extremity of which 

 is clubbed. The following are the principal families of the 

 Lacertilians. 



The first family of importance is that of the Amphisbcznidce, 

 including a number of serpentiform lizards, in which both 

 pairs of limbs are uniformly absent (except in the Mexican 

 Chirotes, in which the fore-limbs are present). All, however, 

 possess a pectoral arch, and they are further distinguished 

 from the Ophidians by the fact that the rami of the lower jaw 

 are united by suture, so as greatly to restrict the gape. The 

 type-genus, Amhisb<zna, is South American, and comprises 

 apodal snake-like lizards with short blunt tails, having the 

 vent situated nearly at the end of the body. 



In the family of the Chaltidida we also have lizards with 

 long snake-like bodies, but minute fore and hind limbs are 

 present. The scales are rectangular, and are arranged in 

 transverse bands which do not overlap. All the members of 

 this group are American. In the nearly allied Zonurida the 

 limbs may be well developed, rudimentary, or wholly wanting ; 

 there is a longitudinal fold of skin_QBr--eali-side of the body ; 



