REPTILIA. 201 



serpentiform Lizards, however, can be distinguished from the 

 true Snakes, amongst other characters, more especially 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 attached behind to a 

 movable quadrate bone, which is in turn connected with a 

 movable squamosal, this giving an enormous width of gape 

 to these animals. In the Lizards however, even in those 

 most like the Snakes, the halves of the lower -jaw are firmly 

 united to one another in front, and though the quadrate 

 bone is usually more or less movable, the jaws can in no 

 case be separated to anything like the extent that charac- 

 terises the Ophidia. 



The Lizards are distinguished from the Crocodiles, amongst 

 other characters, by the fact that the integumentary covering 

 is in the form of horny scales, very rarely accompanied by 

 bony " scutes,", whilst the teeth are rarely sunk into distinct 

 sockets. All the living Lacertilians and almost all the ex- 

 tinct forms possess teeth, which may be confined to the jaws 

 proper, or may be also developed on the palatine and ptery- 

 goid bones. The teeth are always simple, sometimes sharp 

 and conical (Moniio?'), sometimes blade-like, with serrated 

 edges (Iguana), sometimes with broad crushing crowns 

 (Ci/dodus). Usually the teeth become anchylosed with the 

 jaw, becoming either attached by their sides to the parapet 

 of the jaw (" pleurodont " dentition), or fixed by their bases 

 to the top of the parapet (" acrodont " dentition). In the 

 extinct Frotorosaurus the teeth are sunk in distinct sockets 

 (" thecodont " dentition). 



The whole order of the Lacertilia is often united with the 

 next group of the Crocodilia, under the name of Sauria. The 

 term " Saurian," however, is an exceedingly convenient one 

 to designate all the reptiles which approach the typical 

 Lizards in external configuration, whatever their exact na- 

 ture 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. 



It is hardly possible, with our present knowledge, to speak 



