ANATOMY OF SNAKES 



225 



teeth. In the dry skull the distal ends of the dentary 

 bones are free. In some snakes, but not in any of the 

 families that include poisonous species, there is another 

 bone of importance in classification, the coronoid (fig. 97), 

 which forms a sort of internal splint at the upper angle of 

 the splice between the articular and dentary bones. 



The chief bone of the upper jaw, on either side, is the 

 maxilla (ma.), which is usually armed with teeth, and 

 more or less movably attached to the base of the skull. 



tr > 



-ma. 



FIG. 96. 



Between the maxillae is a small, unpaired premaxilla (p.m.) 

 which in all poisonous snakes is toothless. Parallel with 

 the maxillae on either side are the palatines (pi.) and 

 pterygoids (pt.), which form the bony roof of the mouth 

 and are generally toothed : both these bones are largely 

 independent of the base of the skull, and the pterygoid 

 commonly articulates with the quadrate. An important 

 part of the mechanism of the upper jaw is the trans- 

 palatine or ectopterygold bone (tr.), which stretches from 

 15 



