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OP THE INCISURES. 67

when cut down through the middle, but especially in the latter
case, it would seem as if the fang was driven like a wedge into,
and had split the body or Enamel of the Tooth. They stand

divided by a transverse cleft into a strong anterior corneal lobe and a
posterior ridge, wkich is notched vertically, giving to the tooth a three-
lobed configuration. The inferior incisors increase in size from the first
to the third ; the second and third have the crown indented externally,
but they do not present a posterior notched ridge ; the conical points oi*
these teeth fit into the depressions separating the lobes of the incisors
above. The incisive teeth in the Dog form a segment of a circle in both
jaws ; they increase in size from the first to the third ; the edge is divided
by two notches into a large middle and two smaller lateral lobes. In the
most aquatic and piscivorous of the Mustelidce—viz., the Sea-Otter
(Enhydra)—the number of incisors is reduced by the absence of the two
central in the lower jaw ; their number is still farther diminished in
some of the Phocidce: in ths great proboscidian and hooded Seals
(Cystophora) the incisor formula is ff ; they are, however, of large size,
and laniariform, the two outer ones above being largest. In the young
Wahais there are three teeth in each premaxillary above, and two on
each side below ; but they soon disappear, with the exception of the
outer and upper one on each side, which remains on the inner side of
the enormous canine tusk.
The normal number of incisive teeth, fj, which we find in the
extinct herbivorous Dichodon of the eocene tertiary deposits, is replaced
in the existing typical Ruminants by the total suppression of incisors in
the upper jaw, whilst the number six is retained in the lower. In
the hollow-horned Ruminants Antilopidce, Ovidce, and Bovidaz, a callous
pad supplies the place of the upper incisors, albeit their rudiments have
been observed by Professor Goodsir and others in the embryo Sheep and
Cow. The incisors in the lower jaw have low, broad crowns. Upper
incisors are also absent in the solid-horned Cervidce: in the Camels
one laniariform incisor is present in each premaxillary bone. Professor
Owen has described six deciduous upper incisors in the new-born
Dromedary, of larger size than any rudiments of these teeth which exist
in the hollow-horned Ruminants.
The Suidce, or Hog tribe, retain the typical dental formula which is
exemplified in the Chieropotamus, Anthracotherium, and other extinct non-
ruminant Axtiodactyles. In the Hog, the upper incisors decrease in size
from the first to the third ; the central upper incisors are inclined to
each other, and touch by their prolonged inner surfaces ; their crowns are
short, strong, and obtusely pointed : the crown of the second is as broad
as that of the first, but shorter and thinner ; it has a trenchant and
dentated edge, which soon, however, becomes worn clown. The third is
a small tooth separated by a short interval from the second. In the