The bone has been removed to show the embedded parts of the teeth.
(After Ellenberger-Baum, Anat. für Künstler.)
]
=Cheek Teeth= (Premolars and Molars).[83]—The constant number of these
is twenty-four—twelve in each jaw. Quite commonly, however, the number
is increased by the presence in the upper jaw of the so-called wolf
tooth. This tooth is usually situated just in front of the first
well-developed tooth; it is a much reduced vestige, not often more than
one-half or three-fourths of an inch (ca. 1 to 2 cm.) in length. (It is
interesting as being the remnant of a tooth which was well developed in
the Eocene ancestors of the horse.) It may erupt during the first six
months, and is often shed about the same time as the milk-tooth behind
it, but may remain indefinitely. The occurrence of a similar tooth in
the lower jaw—which rarely erupts—increases the dental formula to 44,
which is considered the typical number for mammals. They may be regarded
as belonging to the permanent set, having no predecessors. The cheek
teeth are very large, prismatic in form, and quadrilateral in
cross-section, except the first and last of the series, which are
triangular. The crown is remarkably long, most of it being embedded in
the bone or situated in the maxillary sinus in the young horse. As the
exposed part wears down the embedded part pushes up to replace it, so
that a functional crown of about four-fifths of an inch (ca. 2 cm.) is
maintained. The root begins to grow at four or five years of age, and is
complete at twelve to fourteen, although the deposition of cement may
continue indefinitely.
[Illustration: