90 STORY OF THE REPTILES 



By means of the separation of the lower jaw at 

 the chm, snakes are known from Hzards, and it will be 

 observed that there is a marked difference otherwise. 



The jaws of mammals all have an upward projec- 

 tion upon the jaw itself, which is formed purposely 

 to meet the skull, but in all other creatures the skull 

 itself sends down the bony projection — either loose 

 or securely set in such direction as to meet the jaw. 



The jaws of serpents are rarely used for crushing 

 or killing, but largely for seizing, holding, and slipping 

 the throat over the food, and in the poisonous kinds, 

 for forcing in the fangs. Snakes are strictly swallow- 

 ers, and their whole head-skeleton is arranged for this 

 practice. 



Teeth 



In the reptiles ISTature seems to have experimented 

 with all kinds of teeth. Here she seems to have made 

 useful the w^rinkled or grooved sorts found in the 

 ganoid fishes and labyrinthodont amphibians. She 

 made the grooves the channel for poisons, and even 

 folded some of their edges in till they became tubular. 

 But more of that later. While many lizards and all 

 serpents, perhaps, have teeth somewhere on the roof 

 of the mouth (to speak generally) it was in the rep- 

 tiles that teeth first became confined to the jaws only ; 

 yet, in a few cases, Xature has made the most pre- 

 posterous effort in this class by projecting the lower 

 spines of the back-bone through into the swallow tube 

 and putting enamel upon them, so that several species 

 of serpents which eat eggs may have them broken after 



