208 



OPHIDIA. 



Oca 



formerly regarded as Ophidia. Moreover, many Snakes have tne 

 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 postf rental is not directly connected with the squa- 

 mosal, and there is no jugal or quadrate- 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 

 one another and the 

 cranium, that the mouth 

 is capable of being con- 

 siderably dilated and 

 laterally extended. The 

 quadrate bone is very 

 m o v a b 1 y articulated 

 with the squamosal, 



FIG. 636. Skull of Crotalus horridut. Ocb, Basioccipital ; 

 Ocl, exoccipital ; Oca, supraoccipital ; Pr, prootic ; Bt, 

 Basi-sphenoid; 5j, squamosal ; P, parietal ; F, frontal; which is also movably 

 Pf, post-frontal ; Prf, prse-frontal ; Et, median ethnoid ; . 



N, nasal; Qu, quadrate; Pt, pterygoid ; PI, palatine ; attached On the OCClpl- 

 Mx, maxillary ; Jmx, prse-mazillary ; Tr, transverse j D, 

 dentary ; Art, articulare of the lower jaw. 



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. 

 Hooded teeth may also be present on the praemaxillse (Python). 

 Only in the Opotzrodonta 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 



