648 



. OPHIDIA 



CHAP. 



C'rotalus.— With a rattle. The upper surface of the head is 

 covered with small scales. Eange from Southern Canada and 



5q ^__ flu 



Pmx 



Pms 



Fig. 180. — Skull of a Rattle-Snake, Crotalus durissiis. 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, wliere tlie mechanism has been explained. Gol, Columella anris ; Cond, 

 condyle ; Cr (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', 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. 



