ZOOLOGY. 



Fig. 283. 



they are wholly wanting, as in the serpent; to this may IK- 

 ascribed its fixed look. 



The auditory apparatus is much less complete than in 

 mammals, or even in birds. The external car is almost always 

 completely wanting; there is no auditory canal, and the 

 drum of the ear is on a level with the outer surface of the 

 head ; the tympanic cavity is im- 

 perfectly formed, and seems to be a 

 sort of dependence of the pharynx. 

 The bones of the ear most frequently 

 are wanting, and the cochlea is often 

 rudimentary ; the organs of smell are 

 but little developed; the tongue is sometimes thick and 

 fleshy, but generally thin, dry, and protractile ; in serpents 

 (Fig. 283) and lizards it is bifid : in the chameleon the tongue 

 becomes an instrument of prehension, for it can be darted from 

 the mouth to the distance of several inches, and thus fiies 

 and other small insects are caught by means of a viscous ball 

 which terminates it. 



463. Few reptiles live entirely on vegetable food : they 

 are almost all carnivorous, and pursue a living prey, which 

 they swallow entire. The mouth is almost always* large in 

 the .cleft, and is so dilatable in serpents as to enable them to 

 swallow animals having a larger diameter than themselves. 

 The two branches of the lower jaw (mi, Fig. 284) are united 

 only by ligament, and the tympanic bone (t), and the mas- 



P P 



,< 



Fig. 284. Head of the Crotalus, or American 

 Rattlesnake. 



toidian bone (ma), by means of which the lower jaw is 

 articulated to the cranium, are both moveable, and thus tin- 

 jaws admit of very great dilatation; moreover, the branches 



