I. — Venomous Serpents, with Isolated Movable Fangs. 



Family. CROTALOIDEA. 



These are the most remarkable of the Serpent tribe; their habits and pecuhar 

 properties have caused tliem to be regarded with universal abhorrence, 



CHARACTERS. 



1. The head is generally large; the superior maxillary bones are small, and 



attached by ligaments to a long pedicle, analogous to the external pterrigoid 

 apophysis, 



2. The upper jaw bones are destitute of teeth, but are armed with sharp-pointed, 



pervious, movable fangs, through which the poisonous fluid flows. These 

 fangs are sometimes only grooved — at others there is a complete canal, 

 opening near their extremity, but in all instances these channels communicate 

 with the excretory ducts of the gland. The fangs, when not erect, are con- 

 cealed by a fold in the gum, from which they can be raised at the will of the 

 animal. Behind these are the germs or rudiments of several other fangs, 

 destined to become developed, and to replace the original, should these be 

 destroyed by accident, as not unfrequently happens. 



3. The palate bones are armed with two rows of small, hard, solid, and fixed 



teeth. 



