130 STORY OP THE REPTILES 



pulsate independently as did those whicli first formed 

 the heart in the lowest Yertebrates. These show 

 readily in the wings of bats. 



Skeleton G-eneeallt 



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, which in the 

 tortoise are flattened into plates ; ■/•, ribs ; », shoulder-bone ; a, 

 upper arm ; e, elbow ; fa, forearm ; ft, hip-bone ; fh, thigh-bone ; 

 Tc, knee ; I, bones of the leg ; g, 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 Dinosaurs, however, the 

 vertebrae were often cupped in front, which is a 

 higher form found frequently in the birds and largely 

 among the mammals. 



Keptiles and birds usually make the shoulder junc- 

 tion out of three bones, while mammals have only 



