27G 
IGUANODON 
Fig. 1. is a view of the inner surface of the right 
side of the upper jaw of this animal, of the natural 
size ; and fig. 2. a portion magnified four diameters. 
The teeth are slightly convex externally, and have 
a ridge down the middle ; they are slightly concave 
on the inner surface ; the crown of a tooth, largely 
magnified, is shown, fig. 3. In the angular form 
of the crown, and its serrated edges, they strikingly 
resemble the fossil, fig. 1. page 270 . The new 
teeth are formed at the bases of the old ones, and 
lie in a depression at the root of the fang, as is 
beautifully shown in the magnified drawing, fig. 2., 
at a a. Tlie jaw throws up a lateral parapet on 
the outside of the teeth ; but they have no alveoli, 
nor any internal protection but the gum. From 
the above observations, it appears that the fossil 
teeth bear a greater analogy to those of the recent 
Iguana, both in their form, and in the process by 
which dentition is effected, than to those of the 
crocodiles, monitors, and other living saurians. 
But, notwithstanding this general resemblance, the 
remarkable characters resulting from the act of 
mastication, separate the original animal from aU 
known genera. None of the existing reptiles per- 
form mastication \ their food or prey is taken by 
the teeth or tongue, so that a movable covering 
of the jaws, similar to the lips and cheeks of the 
mammalia, is not necessary, either for confining 
substances subjected to the action of teeth as or- 
gans of mastication, or for the purposes of seizing 
or reaching food.* The herbivorous amphibia 
gnaw off the vegetable productions on which they 
* Rees’s Cyclopa:dia, art. Reptiles. 
