56 THE ORIGIN OF MAN 



Whenever legs are present, the fingers and toes 

 have claws, a feature which is very rare among 

 the Amphibia. Eyelids are present in many rep- 

 tiles and in most lizards, and in most lizards and 

 fossil reptiles the pineal eye is well developed. 

 The organs of smell and hearing are also well de- 

 veloped, but in the reptiles the vibrating, or tym- 

 panic membrane of the ear-drum is no longer ex- 

 ternal, as in frogs, but lies in a depression. All 

 have teeth except turtles and in living forms these 

 are usually pointed and often recurved to serve 

 for the holding of their prey, whereas in the 

 fossil forms they were adapted for cutting and 

 more rarely for the mastication of food. The 

 tongue in snakes and some lizards is slender and 

 protruded in a darting manner, while in other 

 reptiles it is flat and immovable being then at- 

 tached to the floor of the mouth. In some living 

 lizards and snakes the females are viviparous but 

 in the great majority of reptiles, however, the fe- 

 males are oviparous. As the eggs of reptiles de- 



