280 THE VERTEBRATE SKELETON. 



The disposition of the bones of the jaws is subject to 

 much modification in the Ophidia in order to adapt them for 

 swallowing very large prey. The arrangements again differ 

 greatly in the venomous and non-venomous snakes. In the 

 non-venomous snakes, such as Python and Tropidonotus, the 

 palatine is large and is fixed to the pterygoid which extends 

 outwards (fig. 51, 10) so as to be united to the quadrate, and 

 is at the same time firmly connected by the transpalatine with 

 the maxilla. The quadrate is united to the squamosal, which 

 is loosely attached to the cranium. The premaxilla is moder- 

 ately developed and bears teeth, and the maxilla forms a long 

 bar loosely connected with the rest of the skull. The rami of 

 the mandible are united only by an extremely elastic ligament. 

 It is as regards the maxillae and premaxillae that the skulls 

 of venomous and non-venomous snakes differ most. In the 

 rattlesnake (Crotalus) and other venomous snakes the pre- 

 maxilla is extremely small and toothless. The maxilla is 

 small and subcylindrical, and is movably articulated to the 

 lachrymal, which also is capable of a certain amount of motion 

 on the frontal. The maxilla is connected by means of the 

 transpalatine with the pterygoid, which in its turn is united 

 to the quadrate. When the mouth is shut the quadrate is 

 directed backwards, and carrying back the pterygoid and 

 transpalatine pulls at the maxilla and causes its palatal face, 

 to which the poison teeth are attached, to lie back along the 

 roof of the mouth. When the mouth opens the distal end 

 of the quadrate is thrust forward, and this necessitates the 

 pushing forward of the pterygoid and transpalatine, causing 

 the tooth-bearing surface of the maxilla to look downwards 

 and the tooth to come into the position for striking. 



The Ophidian skull is also noticeable for the absence of the 

 jugals and quadratojugals. In poisonous snakes the place of 

 the jugal is taken by the zygomatic ligament which connects 

 the quadrate and maxilla. 



The extent to which the palate is closed in reptiles varies 



