120 MR. II. G. F. SrURRELL OX THE [Feb. 6, 



The mandible of the snake articulates with the quadrate ; the 

 quadrate with the squamosal ; and the squamosal with the 

 parietal (text-fig. 44). 



When the snake wants either to seize its prey or to strike it 

 with the poison-fangs in its maxillfe, it requires a wide gape. To 

 get this, the movement is made at the quadrato-mandibular joint, 

 which can be placed on a level with the teeth. The jaw-principle 

 is then that of type 1 . 



Having seized its prey, the snake, to swallow it, has to advance 

 alternately the teeth in the movable maxilla and those in the 

 mandible on either side. To move the teeth parallel with one 

 anothei-, the movement has to be made from the quadrato- 

 squamosal joint, and so raised above the level of the teeth. The 

 jaw- principle is then that of type 2. 



The parieto-squamosal joint allows the level of the quadrato- 

 squamosal joint to be slightly lowered and brought forwairl ; that 

 is to say, freer antero-posterior and lateral movements to be made, 

 and the passage between the quadrates to be slightly widened 

 (text-fig. 44). 



Text-fi^. 44. 



C 



Diagram of Snaku's jaws. 



A. Squamosal. I C. Mandible. 



B. Quadrate. | D. Maxilla. 



The mandibles on the two sides are, of course, independent 

 anteriorly. 



In most of the reptiles the jaws are of type 1 and are provided 

 with long, sharply pointed and often recurved teeth to prevent 

 the prey from slipping out of the mouth when seized *. These 

 characters of the teeth aie particulai-ly well marked in a beast 

 with a short nuizzle, e. g. the Ceratosaurus. Long teeth are for 

 obvious reasons less necessary in a beast with a long muzzle like 

 the Gavial. The wavy line of the jaws in short-nosed Crocodiles 

 is another device by which the slippings of prey are to be avoided. 



In the Iguanodon, however, the " teeth are not infrequently 

 found worn down at the crown, like the molar teeth of the 

 herbivorous mammalia at the present day" (British Museum 

 Catalogue). " The woi'n down crowns form cutting, and at the 



* I have seeu this accident happen. I gave an Ocellated Lizard a large slug which 

 \\as very slimy and must have been as tough as india-rubber. The lizard picked 

 it u]) and tried to bite it in half as though it were an earthworm, with the result 

 that the slug shot out of its mouth to the distance of some inches. 



