208 



OPHIDIA. 



Ocs 



formerly regarded as Ophidia. Moreover, many Snakes have the 

 rudiments of posterior extremities, which are placed at the root of 

 the tail and have a conical claw projecting at the side of the anus. 

 No Snake has a pectoral girdle or any trace of an anterior pair of 

 extremities. 



In the skull of the Snakes (fig. 636) the temporal arcades are 

 absent [i.e., the postfrontal is not directly connected with the squa- 

 mosal, and there is no jugal or quadrato-jugal connecting the maxilla 

 with the quadrate]. The cranial cavity is very long. The anterior 

 and middle parts of its lateral walls are formed by descending wing- 

 like processes of the 

 parietal and frontal 

 bones. The maxilla is 

 connected with the pa- 

 lato-pterygoid arcade by 

 an os transversum, and 

 these bones are so com- 

 pletely movable upon 



PI Tr pf ) / one another and the 



cranium, that the mouth 

 is capable of being con- 

 siderably dilated and 

 laterally extended. The 

 quadrate bone is very 

 movably articulated 



FIG. G3H. Skull of Crotalus horridtm. Ocb, Basioccipital ; 



Oc/, exoecipital ; Ocs, supraoccipital ; Pr, prootic ; s, With the SquaniOsal, 

 Basi-sphenoid; S 9 , sqiuunosal ; P, parietal ; F, frontal; w bich is also rnoval.lv 

 Pf, post-frontal ; Prf, prw-frontal ; Ei, median ethnoid ; 

 If, nasal; Q, quadrate; Ft, pterygoid; PI. palatine; 

 Jl/.r, maxillary; Jm:r, pra?-maxillary ; Tr, transverse; D, 

 clentary ; Art, articulare of the lower jaw. 



Jl,-t 



attached on the occipi- 

 tal region. The two 

 rami of the lower jaw 

 are as movable as are the parts of the maxillo-palatine apparatus. 

 They are connected at the symphysis by an elastic ligament, which 

 permits of a considerable amount of lateral movement. 



The armature of the jaws consists of a number of recurved pre- 

 hensile teeth, which are arranged in a single row on the lower jaw, 

 and usually in a double row on the maxillo-palatine apparatus ; they 

 chiefly serve to hold the prey fast while it is being swallowed. 

 Hooked teeth may also be present on the pra-maxilla? (Python}. 

 Only in the Opoterodonta are the teeth confined to the upper jaw 

 or to the lower jaw. Besides these solid hooked teeth many snakes 

 possess in the upper jaw grooved teeth, or hollow poison teeth, which 



