442 CHORDATA. 
to the upper surface of the jaw (acrodont), or to the lateral 
surface (pleurodont). The lizards are distinguished from 
their nearest allies, the snakes, by the almost universal pres- 
ence of four limbs, by the bones of the skull being immov- 
able, and the mandibular rami being fused together. They 
also have eyelids. Lizards are widely distributed, but found 
in most profusion in equatorial regions. The common 
slow-worm (with no limbs) and the sand lizard are British 
examples. : 
Fig. 312.-LATERAL VIEW OF SKULL OF 
RATTLESNAKE (Crotalus). 
Note the freely movable quadrate with pterygoid 
continued into small palatine in front and joined to the 
maxilla by a long transverse bone. Maxilla bears the fang. 
OrDER II].—Ophidia. 
The snakes have an exoskeleton of epidermic scales. 
They have no limbs, but progress by a movement of ventral 
scales, to the inner surface of which the distal ends of the 
numerous ribs are attached. Hence there is no sternum. 
The vertebrze usually have extra articular facets (zygosphene 
and zygantrium). The eyes have no eyelids. But in ad- 
dition a unique method of locomotion, the snakes exhibit 
a peculiar method of feeding. The quadrate is loosely 
hinged on the skull, and the maxillz, palatines and pterygoids 
are all freely movable. In addition, the mandibular rami 
