Page 473 - My FlipBook

TEETH OF THE VERTEBRATA.
483
the tooth has been in use for a Httle while, lio\\ever, the lace is worn
down smooth, and the central depression appears bounded by a layer
of enamel, between ^liich and the enamel covering the outer surface' of
Fig. 263.

Skull of Ilippotherium srversum, Cope (after Cope).
the tooth, may be seen the dentine. The incisors are not all cut at the
same time, the last appearing at the age of five years, on account of
which the central pit disappears through wear sooner in those teeth
which are first extruded than those which
are cut last. By observing carefully the
date of appearance of the various inci-
sors, and the consequent difference in time
at which the pits are obliterated in the
different teeth, veterinarians have estab-
lished some very useful rules by which
ace
the age of a horse can be approximately
told wdth considerable certainty up to ten pee
or twelve years.
Canines, or the " bridle teeth," are pre-
sent, but they are of smaller size, and some-
times disappear in the female. The first Molar Tooth of a species of Horse. Let-
ters as in the preceding tigures.
premolars in both jaws are normally ab-
sent, but there are many cases on record in which they are present. In
Hippothenum they are normally present and functional.
The molars present essentially the same pattern as those of the pre-
ceding genus, the only difference of importance being found in the