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76 HUNTER ON THE TEETH.

the side next the Incisores, being there more angular than any
where else.
The Enamel covers more of the lateral parts of these Teeth
than of the Incisores ; they stand perpendicularly, or nearly so,
projecting farther out in the circle than the others, so that the
two Cuspidati and the four Incisores often stand almost in
a straight line, especially in the Lower-Jaw.
This takes place only in adults, and in them only when the
second Teeth are rather too large for the arch of the Jaw ; for
we never find this when the Teeth are at any distance from one

backwards from that point. In the female, the tusks are of much smaller
dimensions than in the male. Their development in the latter is arrested
by castration. A similar tendency to excessive development of the
canine teeth is to be observed in the Hippopotamus. In this animal the
lower canines are extremely massive and large ; the crown is curved and
subtrihedral, the angle dividing the two anterior sides, which are convex
and enamelled, being rounded off ; the posterior side is almost entirely
occupied by the oblique surface abraded by the upper canine. The upper
canines are trihedral, with a wide and deep longitudinal groove behind
;
they curve downwards and outwards ; the exposed part of the crown,
which is worn at the forepart from above obliquely downwards and
backwards, is very short. As in the incisors, the base of the canine is
simple, and excavated for a large, persistent matrix, which insures the
perennial growth of the tooth.
Amongst Perisso-dactyle Ungulates, we find canines present in the
genera Equus and Tapirus, absent in the Rhinoceroses and in the Hyrax.
In the Horse, these teeth are small in the stallion, less in the gelding, and
rudimental in the mare. The upper canines are placed in the middle of
the long interspace which separates the incisors from the premolars. The
crown, when unworn, is characterised by the folding in of the anterior
and posterior margins of the enamel, which includes an extremely thin
layer of dentine. The lower canine, as in Rmninantia, is close to the
incisors, but is of a more pointed shape. In the Tapir, the canines are
of cuspidate form, the crown is much shorter than the root, and
does not project beyond the lips. The outer surface of the crown is
convex, and is divided by sharp margins from a less convex inner sur-
face. The upper canine is separated from the incisors by a short inter-
val, which receives the crown of the lower. The lower forms part of the
same semi-circular series with the inferior incisors. In the Proboscidians
there are no canines. (1)]

(1) Owen, op. cit.