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OS HUNTER ON THE TEETH.
figure, but rather rounder, and its fangs are generally not so
regular and distinct, for they often appear squeezed together
;
and sometimes there is only one fang, which makes the Tooth
anterior and posterior basal tubercles more or less developed. In a few,
however, of the larger species the molars are simple and obtuse. This
is especially the case in the Walrus, in which the molar series is reduced
to a smaller number than in the true Seals, being, in the adult, three on
each side in the upper jaw, and four in the lower. On turning to the
extinct Carnivora, we find in Machairodus two premolars, p. 3 and p. 4,
and one small rudimentary tubercular molar in the upper jaw ; in the
lower the molar series accords with that of Felis. The more ancient
carnivorous forms of the older tertiary formations exhibit the typical
formula of Placental Diphyodont dentition. In Hycenodon each of the
three lower molars present the carnassial form as truly as the lower
carnassiere of the Felidoe. In another early carnivore (Amphicyon), with
the same typical number of teeth, the molars have the tubercular con-
formation—the prototypes of the tubercular molars of the Viverridce and
Canidce.
The study of the grinding teeth in the various vegetable feeders, is
assisted and simplified by a reference to the forms of those teeth in the
fossil remains of early herbivora, occurring in the eocene or most ancient
tertiary formations. In the Anoplotherium, the crown of the upper
molar is divided into a front and back lobe, by a valley which extends
from its inner side two thirds across. A second valley, crosses its ter-
mination at right angles, and forms a crescentic depression in each lobe,
concave towards the outer side of the crown—the side of the crown
being impressed by two parallel excavations. There is a large conical
tubercle at the entrance of the transverse valley on the inner side of
the crown. This type is continued into the Dichodon, Dichobunes
and existing Ruminants. The dentition of the Dichodon, an extinct
genus, the remains of which have been found in the upper eocene of
Hampshire, forms a transitional link between that of the Anoplotherium
and the present Ruminants. The Dichodon presented the typical
formula p. %\ ^[
, m. f] £ \ . The crowns of the first three premolars are
extended from before backwards, each presents three progressively
developed and pointed cusps on the same line ; to the third in the
upper jaw, a fourth inner and posterior cusp is added. The fourth pre-
molar is thicker and shorter from before backwards, and has two pairs
of cusps. The crowns of the upper true molars have also each two
pairs of sharp-pointed cusps, and also a series of five low accessory
points, developed from the outer part of the cingulum. The lower
molars have crowns of the same complex character as those above, but
the convex side of the principal cusps are turned in the opposite
direction to those of the upper, and the accessory basal points arc