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OP THE GRINDERS. 101
In the Upper-Jaw this third Grinder is turned but a very
little outwards ; is frequently inclined somewhat backwards
and it projects over that of the Under-Jaw. It oftener be-
comes loose than any of the other Teeth.
posterior surface. This type is the fundamental pattern of the upper
molars of the Horse and Ehinoceros. The formula of the molar series in
. The crowns of the upper molars bear some
the Horse i&p.% f '. in. f \ f \
'.
resemblance to those of the Ruminants in their complexity. The re-
semblance of the crowns of the lower molars to those of the Rhinoceros
and Palceotherium is more marked. The grinders of the Horse may be
distinguished from the complex teeth of other Herbivora of an equal
size by the great length of the tooth before it divides into fangs.
Abrasion of the crown goes on to a considerable extent before the
division begins ; hence, except in old horses, a considerable portion
of the whole molar is implanted by an undivided base. In the
Rhinoceros, the likeness of the crown of the molar to that of the
Palceotherium is very obvious. The differences in the upper molar
are chiefly that two concavities which exist on the outer side of
the crown in Palceotherium are almost levelled in the Rhinoceros ;
that the termination of the oblique transverse fissure in the
Rhinoceros is more expanded, and in some species bifurcates and
deepens, so that in the worn crown one branch may form an insulated
circle of enamel. The posterior valley is also deeper and more extended.
A basal ridge girts the internal and anterior and posterior sides of the
crown. The formula of the grinding series in the Rhinoceros is
• t. t. "* y- 7- •
A fourth type is furnished by the molars of the Lophiodon. They are
nearly allied, in configuration, to those of Palceotherium, but they have a
more decided transversely ridged character. This configuration obtains
in the Dinotherium and the existing Tapies.
The Proboscidean Family. Certain extinct species of proboscidians
received from Cuvier the name of " Mastodon," in consequence of the
peculiar conformation of their grinding teeth, which appeared to place
them in a distinct group from the existing Elephant. Subsequently, how-
ever, other fossil remains of proboscidians have been discovered in the ter-
tiary deposits of tropical Asia, which establish the transitional characters
between the lamello-tuberculate teeth of the elephants and the mam-
milated molars of the typical Mastodous, showing that the distinctions
deducible from their molar teeth rather establish differences of species
than of genera. In the Mastodon giganteus and M. angustidens, the
grinding surface of the molar, instead of being cleft into numerous thin
plates, as in the Elephant, was divided into wedge-shaped, transverse
ridges, the summits of which were again divided into conical protu-
berances, more or less resembling the teats of a cow. The crown of the
N
OP THE GRINDERS. 101
In the Upper-Jaw this third Grinder is turned but a very
little outwards ; is frequently inclined somewhat backwards
and it projects over that of the Under-Jaw. It oftener be-
comes loose than any of the other Teeth.
posterior surface. This type is the fundamental pattern of the upper
molars of the Horse and Ehinoceros. The formula of the molar series in
. The crowns of the upper molars bear some
the Horse i&p.% f '. in. f \ f \
'.
resemblance to those of the Ruminants in their complexity. The re-
semblance of the crowns of the lower molars to those of the Rhinoceros
and Palceotherium is more marked. The grinders of the Horse may be
distinguished from the complex teeth of other Herbivora of an equal
size by the great length of the tooth before it divides into fangs.
Abrasion of the crown goes on to a considerable extent before the
division begins ; hence, except in old horses, a considerable portion
of the whole molar is implanted by an undivided base. In the
Rhinoceros, the likeness of the crown of the molar to that of the
Palceotherium is very obvious. The differences in the upper molar
are chiefly that two concavities which exist on the outer side of
the crown in Palceotherium are almost levelled in the Rhinoceros ;
that the termination of the oblique transverse fissure in the
Rhinoceros is more expanded, and in some species bifurcates and
deepens, so that in the worn crown one branch may form an insulated
circle of enamel. The posterior valley is also deeper and more extended.
A basal ridge girts the internal and anterior and posterior sides of the
crown. The formula of the grinding series in the Rhinoceros is
• t. t. "* y- 7- •
A fourth type is furnished by the molars of the Lophiodon. They are
nearly allied, in configuration, to those of Palceotherium, but they have a
more decided transversely ridged character. This configuration obtains
in the Dinotherium and the existing Tapies.
The Proboscidean Family. Certain extinct species of proboscidians
received from Cuvier the name of " Mastodon," in consequence of the
peculiar conformation of their grinding teeth, which appeared to place
them in a distinct group from the existing Elephant. Subsequently, how-
ever, other fossil remains of proboscidians have been discovered in the ter-
tiary deposits of tropical Asia, which establish the transitional characters
between the lamello-tuberculate teeth of the elephants and the mam-
milated molars of the typical Mastodous, showing that the distinctions
deducible from their molar teeth rather establish differences of species
than of genera. In the Mastodon giganteus and M. angustidens, the
grinding surface of the molar, instead of being cleft into numerous thin
plates, as in the Elephant, was divided into wedge-shaped, transverse
ridges, the summits of which were again divided into conical protu-
berances, more or less resembling the teats of a cow. The crown of the
N
