294 VERTEBRATES : REPTILES. 



composed of large bony plates embedded in the skin. 

 They have very long jaws, large conical teeth placed in 

 sockets in a single row, a fleshy tongue fixed to the bot- 

 tom of the mouth, nostrils at the end of the snout, lungs 



Fig. 156. 



Alligator, A . mississippiensis, Gray. 



that do not extend into the abdomen, and a heart with 

 four cavities. In the living species the vertebrae are 

 concave on their anterior face, and convex on their pos- 

 terior, and the sacrum is composed of two vertebrae. 



The Lacertians are scaly saurians, and they embrace 

 all the true Lizards, Iguanas, Chameleons, Geckos, &c. 

 Several families, genera, and species are briefly described 

 in the next six pages. 



The Enaliosaurs are swimming saurians known to us 

 only by their fossil remains. Their limbs were paddle- 

 like. The Ichthyosaurus was a swimming saurian, from 

 ten to forty feet in length, with jaws six feet long ! 



The Plesiosaurus was a swimming saurian, from twenty 

 to forty feet long, with a long neck containing from 

 twenty to forty vertebrae. 



The Pterosaurs, or Flying Saurians, represented by the 

 Pterodactyl, are also extinct. They were a foot or more 

 in length, with a spread of wing of three feet 



