206 



THE ANATOMY OF VERTEBRATED ANIMALS. 



base of the skull. And all these arrangements, taken together, 

 allow of that immense distention of the throat which is requi- 

 site for the passage of the large and undivided prey of the 

 serpent. 



In Tortrix, this mechanism does not exist, the short quad- 

 rate bone being directly articulated with the skull, while the 

 squamosal, like the post-frontal, is rudimentary. The maxillary 

 bones are also almost fixed to the skull. 



In the Rattlesnakes ( Crotalus^ Fig. 74), the premaxillse 

 are very small and toothless. The maxillary bone has no 

 longer the form of an elongated bar, but is short, subcylindri- 

 cal, and hollow ; its cavity lodges the fossa formed by the in- 

 tegument in front of the eye, which is so conspicuous in these, 

 and sundry other, poisonous Snakes. The upper and inner 

 part of the maxilla articulates with a pulley-like surface fur- 

 nished to it by the lachrymal, so that the maxilla plays freely 

 backward and forward upon that bone. The lachrymal, again, 

 has a certain amount of motion upon the frontal. The upper 

 edge of the posterior wall of the maxilla is articulated by a 

 hinge-like joint with the anterior end of the transverse bone, 

 which has the form of an extremely elongated and flattened 

 bar connected posteriorly with the pterj^goid. 



A^a La-- 



jT (J. 74.— A, the skull of Crotahts, viewed from the left side; B, a transverse secUoTi takrn 

 at the point B, in Fij^. A, showing' T, the persistent cartila^nous trabeculse. The niiix- 

 llla is supposed to be ti-anspareut, and the anterior half of the palatine bone is BOt>n 

 through it. 



