546 MANUAL OF ZOOLOGY. 



or Ophidians in external appearance. These serpentiform 

 Lizards, however, can be distinguished from the true Snakes, 

 amongst other characters, more especially by the structure of 



Fig. 301. Iguana. 



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, how- 

 ever, 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 general character is to be found in the struc- 

 ture 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, including most 

 of 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 typical 

 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. Whatever the condition of the 

 limbs may be, there is, however, always a pectoral arch more 

 or less completely developed, even though the pelvic arch 

 should be wanting. 



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 



