648 



OPHIDIA 



CHAP. 



Crotalus. With a rattle. The upper surface of the head is 

 covered with small scales. Range from Southern Canada and 



Prru 



Prf 



iv\a* 



Prux 



Pmx 



FIG. 180. Skull of a Rattle-Snake, Crotalus durissus. x 1. A, Lateral view, jaws 

 slightly opened ; B, ventral view ; C, lateral view, the jaws opened fully in the 

 position of striking ; D, dorsal view. Compare this with the diagrammatic figures 

 on p. 588, where the mechanism has been explained. Col, Columella auris ; Oond, 

 condyle ; Or (in B), sphenoidal crest for the attachment of the powerfully developed 

 ventral cranio-cervical muscles ; E. P, ectopterygoid or transverse bone ; F, frontal ; 

 Max, maxillary ; P, parietal ; P 1 , post-orbital process ; Pal, palatine ; Pmx, pre- 

 maxillary ; Pr.f, prefrontal ; Ptg, endopterygoid ; Q, quadrate ; Sq, squamosal. 



British Columbia to Northern Argentina, but not in the West 

 Indian Islands. About ten, mostly closely-allied species. 



