IGUANOUON. 247 
of these is a sharp and serrated edge, extending 
on each side downwards, from the point to the 
broadest portion of the body of the tooth. (See 
Figs. 1, 2, 6, 8, 12, &c.) 
The second provision is one of compensation 
for the gradual destruction of this serrated edge, 
by substituting a plate of thin enamel, to main- 
tain a cutting power in the anterior portion of the 
tooth, until its entire substance was consumed in 
service.^ 
Whilst the crown of the tooth was thus gra- 
dually diminishing above, a simultaneous ab- 
sorption of the root went on below, caused by 
the pressure of a new tooth rising to replace the 
old one, until by this continual consumption at 
both extremities, the middle portion of the older 
tooth was reduced to a hollow stump, (Figs. 10, 
11), which fell from the jaw to make room for a 
* This perpetual edge resulted from the enamel being placed 
only on the front of the tooth, like that on the incisors of Ro- 
dentia. As the softer material of the tooth itself must have worn 
away more readily than this enamel, and most readily at the part 
remotest from it, an oblique section of the crown was thus perpe- 
tually maintained, with a sharp cutting edge in front, like that of 
the nippers. (See Figs. 7. 8. 12.) 
The younger tooth, (Fig. 1), when first protruded, was lancet- 
shaped, with a serrated edge, extending on each side downwards, 
from the point to its broadest portion, as in the living Iguana. 
(PI. 24./'. 13, and Fig. 4.) This serrature ceased at the broadest 
diameter of the tooth, i.e. precisely at the line, below which, had 
they been continued, they would have had no effect in cutting. 
(PI. 24. f. 2. 6. 8. 9. 12.) As these saws were gradually worn 
away, the cutting power was transferred to the enamel in front, 
