MYOLOGY OF EEPTILES. 



227 



pents : the long tympanic bone, fig. 97, 28, is suspended by its 

 extremity from that of the outstanding- mastoid ; and besides the 

 movements of swinging to and fro to the extent allowed by the 

 loose articulations of the upper jaw, it is affected by the muscles 

 tending to divaricate the mandibular rami, as well as by a 

 muscle directly drawing its lower end outward. This latter re- 

 peats the levator tympanici of Fishes, fig. 134, 24 : but, with the 

 retrograde course of the ophidian tympanic, its levator has a 

 more posterior origin, viz. from the end of the mastoid, and is 

 inserted into the lower, instead of the upper, end of the tympanic. 

 To counteract these movements, we find a muscle answering 

 to the ' depressor tympani' of Fishes, fig. 136, 22, which arises 

 from the basi-occipito-sphenoid, fig. 146, m, and passes trans- 

 versely outward and backward to the lower end of the tym- 

 panic and co-articulated end of the mandible : it depresses the 

 tympanic and draws it and the articular part of the mandible 

 inwards. 



Of the muscles which close the mouth, one, like the muscle /, 

 fig. 132, of the Shark, bears analogy to the masseter; in the 

 absence of a zygoma, it arises from the postfrontal and contiguous 

 part of the ectopterygoid, fig. 145, e, passes backward, winding- 

 round the tympano-mandibular joint, and is inserted into the 

 surangular and angular, as far forward as the dentary. In 

 venomous snakes its fascial origin spreads over the poison-bag, 

 lb. a. The temporalis, 

 ib. i, arises from the 

 side and spine of the 

 parietal, and descends 

 almost vertically, partly 

 covered by the mas- 

 seter, to be inserted into 

 the coronoid plate. The 

 post-temporalis, ib. f, 

 arises from the fore part 

 of the mastoid and con- 

 tiguous part of the pa- 

 rietal, and descending 

 in front of the tympa- 

 nic is inserted into the coronoid ridge nearer to the joint of the 

 lower jaw. 



The ' tympano-mandibulamsj ib. g, which is analogous to the 

 digastricus, or its hinder belly in Mammals, arises from the back 

 part of the tympanic, and is inserted into that of the angular 



Q 2 



Muscles of the jaws, Orotalus. cxcil. 



