LACERTILIA AND CROCODILIA. 409 



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 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 characterises the 

 Ophidia. 



Another good and still more obvious character is to be found 

 in the structure of the protective coverings of the eye. In the 

 Snakes eyelids are wanting, and the eye is simply covered by 

 a layer of epidermis, constituting the so-called '' antocular 

 membrane." In almost all the Lizards, on the other hand, in- 

 cluding all the completely snake-like forms, there are movable 

 eyelids, and in few cases is there any structure comparable to 

 the antocular membrane of the true Snakes. Lastly, the typi- 

 cal Lizards all possess a sternum or breast-bone, but this is 

 wanting in some of the snake-like forms, so that it cannot be 

 appealed to as a character by which the Lacertilia can be se- 

 parated from the Ophidia. 



The whole order of the Lacertilia is very 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 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 im- 

 perfectly known. It is therefore perhaps best to employ this 

 term merely in a loose general sense. 



The Lacertilia are often divided into the two great groups of 

 the Fissilinguia and Brevilinguia, according as the tongue is 

 bifid and protrusible like that of the Ophidians, or is thick and 

 fleshy, and only protrusible when the mouth is open. These 

 distinctions, however, are not of any very great value, and no 

 good general arrangement of the order has hitherto been pro- 

 posed. Here, therefore, it will be sufficient to treat very 

 shortly of the more important families of the Lacertilians. 



The first family of any importance is that of the Amphisban- 

 ida, comprising a number of snake-like animals which have 

 long occupied a debatable position. In their serpentiform 

 cylindrical form these animals closely resemble the true Ophidia, 



