Chapter IV 

 LACERTILIA— LIZARDS 



Even the most casual observer cannot fail to distinguish 

 lizards from tortoises, while the absence of a movable 

 tongue, and the longitudinal cleft of the vent, are characters 

 by which a Crocodilian can at once be separated from any 

 type of lizard, to say nothing of the dentition and various 

 anatomical characters which do not appeal to the super- 

 ficial observer. From snakes, however, the distinction is 

 not so apparent, for, although the great majority of lizards 

 have four well-developed limbs, provided with five clawed 

 digits, it must be borne in mind that in a number of 

 families there is a tendency to lose these organs, and for 

 the toes to become gradually reduced, and that in a few 

 degenerate types, such as our Common Slow-worm, they 

 are even entirely absent. Rudiments, at least, of both 

 pectoral and pelvic girdles are, however, always present. 

 The possession of eyelids and ear-openings is the general 

 rule, but here again there are exceptions, and too much 

 reliance cannot therefore be placed on these external 

 features. In the structure of the lower jaw, however, 

 we have a character by means of which the two orders 

 may be most conveniently separated, for in lizards the 

 mouth is non-expansible, the two halves of the lower jaw 



51 



