130 STORY OF THE REPTILES 



pulsate independently as did those wliicli first formed 

 the heart in the lowest Vertebrates. These show 

 readily in the wings of bats. 



Skeleton Generally 



Much has been said already of the bones of the 

 reptiles as we have come along. This class is more 



Fig. 59. — Skeleton of a lizard, sp, spinous processes, wliicli in the 

 tortoise are flattened into plates ; r, ribs ; s, shoulder-bone ; a, 

 upper arm; e, elbow; fa, forearm; /;, hip-bone; th, thigh-bone; 

 h, knee ; /, bones of the leg ; q, quadrate bone between upper and 

 lower jaw. 



bony than the amphibians, though some of the an- 

 cient forms had the old soft gristly string yet inside 

 of the rings of bones which made up their spinal 

 columns ; and the gecko tribe (Fig. 60) has something 

 similar yet. In geckos the vertebrae are cupped at 

 both ends ; in most others they are cupped back and 

 round in front. In the old Dinoscncrs, however, the 

 vertebrae were often cupped in front, which is a 

 higher form found frequently in the birds and largely 

 among the mammals. 



Reptiles and birds usually make the shoulder junc- 

 tion out of three bones, while mammals have only 



