_I^1_, _I^2_, _I^3_, Incisors; _C_, canine.
]
This fact is of value in the determination of age by the teeth, since
the table surface at different ages represents a series of such
cross-sections. As the exposed crown wears down the embedded part
(reserve crown) pushes up out of the alveolus, so that the tables of the
first and second lower incisors are at first oval, with the long
diameter transverse; later—at about fourteen years usually for the first
lower incisors—the tables are triangular, with the base at the labial
edge. At the same time the infundibulum or cup becomes smaller,
approaches the lingual border, and finally disappears; it remains longer
on the upper incisors, as it is deeper in them. Another marked feature
in old age is the progressive approach to a horizontal direction as seen
in profile; at the same time the teeth become parallel and finally
convergent.
=Canine Teeth.=—These are four in number in the male; in the mare they
are usually absent or rudimentary.[82] They interrupt the interdental
space, dividing it into two unequal parts. The upper canine is situated
at the junction of the premaxilla and the maxilla; the lower canine is
placed nearer the corner incisor. The canines are simple teeth, smaller
than the incisors, and are curved with the concavity directed backward.
The crown is compressed, convex, and smooth externally; concave with a
median ridge internally; its edges are sharp, and the apex is pointed in
the unworn tooth. The root is round and the pulp cavity is large,
persisting to advanced age.
[Illustration:
FIG. 248.—LONGITUDINAL SECTION OF PERMANENT INCISOR TOOTH OF HORSE,
ABOUT NATURAL SIZE.
]
[Illustration:
FIG. 249.—INCISOR TOOTH OF HORSE, LINGUAL ASPECT. (After
Ellenberger-Baum, Anat. für Künstler.)
]
[Illustration: