24f) GIGANTIC TEIIRKSTRIAL SAURIANS. 
The examination of these teeth will lead us to 
the discovery of remarkable contrivances, adapt- 
ing them to the function of cropping tough ve- 
getable food, such as the Clathraria, and similar 
plants, which are found buried with the Igua- 
nodon, might have afforded. We know the form 
and power of iron pincers to gripe and tear 
nails from their lodgment in wood : a still more 
powerful kind of pincers, or nippers, is con- 
structed for the purpose of cutting wire, which 
yields to them nearly as readily as thread to a 
pair of scissors. Our figures (PI. 24, Figs. 6, 
7, 8, 12) show the place of the cutting edges, 
and form of curvature, and points of enlargement 
and contraction, in the teeth of the Iguanodon, 
to be nearly the same as in the corresponding 
parts of these powerful metallic tools; and the 
mechanical advantages of such teeth, as in- 
struments for tearing and cutting, must have 
been similar.* 
The teeth exhibit also two kinds of provisions 
to maintain sharp edges along the cutting 
surface, from their first protrusion, until they 
were worn down to the very stump. The first 
• Fig. 2. represents the front of a young tooth; and Figs. .5, 
6, 7, 8, the front of four other teeth, thrown slightly into profile. 
In all of these we recognise a near approach to the form of the 
nipping pincers, with a sharp cutting edge at the upper margin of 
the enamel. The enamel is here expressed by wavy lines, which 
represent its actual structure : it is placed only in front, like the 
enamel in front of the incisors of Rodentia. 
