648 



OPHIDIA 



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

 covered with small scales. Eange from Southern Canada and 



Pmx;, 



Pra^ 



Fig. ISO. — Skull of a Rattle-Snake, Crotalus durissj/s. 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. Vol, Columella auris ; Cnnd, 

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

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

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

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



British Columbia to Northern Argentina, but not in the West 

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



