LACERTILIA AND CROCODILIA. 



461 



no hind-feet; in some (Bipes] the fore-limbs are wanting ; and 

 others (Angitis, Pseudopus, and Amphisbcsna) are entirely desti- 

 tute 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 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. 



Fig. 199. Iguana. 



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 

 separated from the Ophidia. 



The whole order of the Lacertilia is very often united with 

 the next group of the Crocodilia, under the name of Sauna. 

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

 one to designate all the Reptiles which approach the typical 



