TEETH OF REPTILES AND FISHES. 
17 5 
like the duck, upon the water-insects, shell-fish, and aquatic 
plants, that it obtains from the mud, into which it is continu¬ 
ally plunging its singular bill; and its jaws, entirely destitute 
of teeth, are furnished with horny ridges, by which it can in 
some degree masticate its food. 
187. Among Birds, there is an entire absence of teeth; 
and the mechanical division and the reduction of food is per¬ 
formed in the stomach, in the manner hereafter to be men¬ 
tioned (§ 200). The mouths of almost all Beptiles, excepting 
the Turtle tribe, are furnished with numerous teeth (fig. 
104) ; but these are not 
adapted for much variety of 
purposes, being principally 
destined to prevent the 
escape of the prey which 
the animals have Secured ; Fi ^* 104 -— Head of Gavial. (Crocodile 
and their shape is conse¬ 
quently nearly uniform, being for the most part simply 
conical. There are some Lizards, however, which are herbivo¬ 
rous ; and these have large rough teeth, somewhat resembling 
the molars of Mammalia. The Iguanodon, an animal of this 
tribe, attained a gigantic size in past ages of the world. 
188. In Fishes, the teeth are commonly very numerous (fig. 
105) , but they have for their object only to separate and retain 
Fig. 105. —Head of Shark. 
their food; and there is little variety in their form. Fre¬ 
quently they have no bony attachment, being only held by 
the gum, as in the Shark; and they are consequently often 
torn away, but they are as readily replaced. Sometimes, how- 
