DNA Animal Life 
modern true reptiles are furnished with teeth which, although structurally very similar 
to those of mammals, yet display important differences in other respects. One notable 
feature in which the dentition of reptiles as a whole differs from that of mammals is 
that the teeth, in place of being strictly confined to the margins of the two jaws, 
may be present on some of the bones of the palate, as im snakes and the monitor 
lizards. Then again, the teeth of modern reptiles, which are generally very numerous, 
differ from those of mammals in their mode of replacement and succession. In 
mammals, as we have seen in the preceding article of this series, there are never 
more than two sets of teeth developed, the number of 
each of which is, as a rule, definite and invariable. In 
existing reptiles, on the other hand, there is nothing of 
this definiteness and limitation, the new teeth replacing 
the old ones from beneath im an irregular manner 
throughout life, as is shown in the accompanying sketch 
of part of the jaw of a crocodile. Frequently, indeed, 
the imperfectly developed hollow crowns of quite a 
number of teeth, stacked like thimbles and destined to 
replace one another vertically, may be detected within the 
hollow of the jaw of a crocodile. Fig. 2. Part of the Jaw of a Crocodile, 
he ria 0 0 to show Irregular Replacement of the 
Among existing reptiles, the teeth of crocodiles are Teeth, 
peculiar on account of the 
circumstance that they are set 
in separate sockets. In lizards, 
on the other hand, the teeth 
(except, of course, those on 
the palate) are generally 
soldered either to the summits 
of the jaws or to the inner 
side of the raised outer wall 
of the same, although they are 
sometimes In an open groove. 
Much the same conditions 
obtain with regard to the 
marginal teeth of serpents. 
Although in crocodiles 
some are larger than others, 
there is generally no division of 
the teeth in modern reptiles 
into groups corresponding to 
the incisors, tusks, and molais 
of mammals; neither do any 
of the lateral teeth ever develop 
two or more distinct roots. 
On the contrary, if we except 
the specially modified poison-fangs of the venomous serpents, most or all of the teeth 
of the great majority of reptiles of the present day are of the same general type and 
take the form of simple one-rooted cones, although their sumnuts may be more or 
less compressed or depressed, while in some cases, as in the iguanas, the summits 
and fore-and-aft ridges may be serrated. 
Compared with those of mammals, the teeth of modern reptiles are evidently of a 
much less advanced type, those of crocodiles being comparable, so far as form and 
Fig. 4. Jaws of an Alligator. 
