THE REPTILES 189 



thick-set and muscular, and provided with horny jaws 

 entirely destitute of teeth, like those of the birds. The 

 limbs also are usually short and thick and variously shaped, 

 and adapted for aquatic or terrestrial locomotion. The 

 number of vertebrae in the body and tail are relatively few, 

 and the thick and heavy body is devoid of the elements of 

 grace and agility of movement characteristic of the other 

 reptiles. On the other hand, the former enjoy a freedom 

 from the attacks of enemies not accorded to animals in 

 general. 



At first sight the appearance of a turtle does not indi- 

 cate a close relationship to the other reptiles, but a more 



FIG. 113. Box-turtle (Terrapene Carolina). 



careful examination, and especially of their development, 

 discloses a remarkable resemblance. The head, tail, and 

 limbs are essentially similar to those of the lizards, but in 

 the trunk region peculiar modifications have taken place. 

 The ribs at first separate, as in other animals, flatten 

 greatly, and unite with a number of bones embedded in 

 the skin, thus forming one great plate overlying the back 

 of the animal. About the circumference of the shield 

 other dermal or skin-bones are added, which increase the 

 area of the carapace, and at the same time still others have 



