I40 WATER REPTILES OF THE PAST AND PRESENT 



LIZARDS 



Popularly a lizard is any four-legged reptile covered with 

 scales, but such a definition is not strictly correct, since some 

 lizards are legless and some other four-legged reptiles are covered 

 with horny scales, notably the tuatera or Sphenodon of New 

 Zealand, a reptile long classed with hzards, but now known to 

 belong to quite a different order. Bearing in mind those characters 

 given as characters of the order, it will be necessary to mention 

 only those distinguishing the lizards from the snakes. 



It is true that the great majority of lizards have four legs, while 

 the snakes are always functionally legless, but there are some 



Fig. 65. — Iguana. {By permission of the New York Zoological Society) 



lizards, like the glass snakes and the amphisbaenas, or slow lizards, 

 which are quite legless and there are some snakes which have small 

 but functionless hind legs. As usual, more important differences 

 are found in the skull. The brain-case in all snakes is surrounded 

 on all sides by bone, for the better protection of the brain, with the 

 head resting quite prone on the ground. The brain of the lizards, 

 for the most part, is protected on the sides and in front by a simple 

 membrane. Nearly all lizards have movable eyelids, while snakes 

 do not; snakes have a single lung, and a protrusible tongue, which 

 very few hzards possess; and the lower jaws in front are united 

 in the snakes by a ligament only. Notwithstanding these differ- 

 ences, the snakes and lizards are closely related animals, and must 



