IGUANODON 
274 
entire angular part of the tooth and its dentated 
edges disappear. If we trace the effects of this 
operation still farther, we find it going on as in 
figs. 4}^ 5. p. 270., till it reaches its maximum in 
fig>S., which is merely a bony plate, without a fang, 
and with but a slight portion of enamel remaining on 
the anterior part. The process by which these 
changes have been effected is clearly that of mas- 
tication. So soon as the tooth performs its part in 
that operation, its point is, by degrees, worn away, 
till, by little and little, the serrated edges dis- 
appear, and the tooth assumes a truncated form ; 
the masticating surface gradually becomes larger, 
and is always oblique (because the anterior coat of 
enamel is, from its superior thickness, less used 
than the rest of the tooth), till the tooth is worn 
down to the gum. During these changes in the 
crown of the tooth, the fang is suffering destruc- 
tion from another but not less certain, process. A 
new tooth is formed at the base of the old one, 
which, increasing in size, occasions the absorption 
of the fang of the latter, till at length, when it is 
sufficiently developed, it displaces its predecessor, 
and occupies its place. The gradual progress of 
this change is shown in fig. 2. a p. 27O. ; and in 
fig. 4. of the same, in which the impression of the 
new tooth, or dent de reynplacement^ is marked a. ■ 
The teeth are hollow in the young animal, but 
become solid, almost throughout, in the adult state. 
If we attempt to discover among the recent 
lizards a dentature at all analogous, we sliall find 
among the Iguanas alone any kind of resemblance ; 
yet even here, we cannot fail to remark, that in 
this, as in every otlier instance, if there be a general 
