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90 HUNTER ON THE TEETH.

second ; it is turned a little more inwards than the adjacent
Bicuspides, but not so much as the second Grinder. Both of
them have generally shorter fangs than the Bicuspides.

which subsist on the coarser and less nutritious kinds of vegetable
tissues, and whose molars, consequently, are subject to more rapid wear.
Such are the Beaver, the Agouti, &c. In them, for a considerable
period, the wear of the crown is compensated for by the continued repro-
duction of the formative matrix, and during this time, the tooth is im-
planted by a simple, undivided continuation of the crown. When the
formative force becomes exhausted, the matrix is simplified by the sup-
pression of the enamel organ, and the dentinal pulp continues to be
reproduced only at certain points of the base of the crown, which, by
their elongation, constitute the fangs. In a third category, which con-
tains the Cavies, the Capybara, &c, the molars, like the incisors, are
perpetually growing, and rootless. These teeth are always more or less
curved, by which conformation, as in the case of the incisors, the effects
of pressure, transmitted from the grinding surface, on the soft and deli-
cate growing structures at the base of the tooth are obviated. It is in
the rootless molars of the strictly herbivorous Rodents that the com-
plexity of the crown is greatest, and that the largest proportion of
enamel and cement is interblended with the dentine. In the omnivorous
Rats and Mice, the tuberculate molars are almost as simple as the cor-
responding teeth in the Bears or in Man, which they may be said to
typify. In the herbivorous Rodents, we find folds or islands of enamel
interposed between the layers of cement and dentine, and, as was
pointed out by Baron Cuvier, they have a general transverse arrange-
ment across the crown of the tooth, the opposite to the direction of the
temporo-maxillary articulation. The different arrangements of the
enamel, dentine, and cement, in the molars of different genera of
Rodents, present interesting analogies to the modifications which the
arrangements of the same substances undergo in the molars of the
different species of Elephant, the Rhinoceros, the Hippopotamus, Rumi-
nants, &c. The molars, although not numerous, vary in number in the
different genera. In the Hares and Rabbits, the formula is f ; in the
; \\
Pika (Lagomya), f ; £ ; in the Squirrels, | .' || ; in the Dormice, Porcu-
J i° the
pines, Spring-Rats, Octodonts, Chinchillas, and Cavies, £."!'
Rats, f ; 4; ; in the Australian Water-Rat, %\ \\ ; making, with the
two incisors in each jaw, twelve teeth, the smallest number known in
any Rodent. When the teeth of the molar series exceed three in
number, those anterior to the posterior three are premolars, having dis-
placed deciduous molars, and come into place after the true molars, at
least after the first and second, even when the deciduous teeth are shed
in utero.
Order Quadrumana. In the genus Clteiromys, which manifests a dis-