648 



OPHIDIA 



CHAP. 



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

 covered with small scales. Eantie from Southern Canada and 



Pm,n 



Pmx 



Pmx 



Fig. 180. — Skull of a Rattle-Snake, Crotalus durissns. x 1. A, Lateral view, jaws 

 slightly openeil : B. vuntral view ; C, lateral view, the jaws opened fully in the 

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

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

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

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

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

 maxillary ; Pr.f, prefrontal ; P/;/, eudopterygoid ; Q, quadrate ; S(2> squamosal. 



British Columbia to Northern Argentina, but not in the West 

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



