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82 HUNTER ON THE TEETH. —
The body forms almost a square, with rounded angles. The
grinding surface has commonly five points, or protuberances,
tooth. The effects of attrition on that surface are compensated by the
continued growth of the denticles. In the Armadillos (Dasypus)
the dental organs attain the greatest degree of hardness found in the
order. Each tooth consists of a small central axis of vascular dentine,
surrounded by a body of ordinary dentine, which forms the principal
bulk of the tooth, and the external surface of which is covered by a thin
layer of cement. The teeth in the great Armadillo (Priodon gigas),
amounting to from 94 to 100 in number, are all to be classed as molars.
They are of small size, simple in form, and they increase, especially in
breadth, from before backwards. The implanted portion of the tooth is
as thick as the uncovered part, and is widely excavated for a persistent
pulp. The'dentition in the great extinct Armadillo (Glyptodon), presents
a conformation more complex, and better adapted for vegetable feeding
than that of the existing species. The tooth of the Glyptodon is long
and rootless, as in the existing Armadillos ; it is compressed laterally,
and deeply indented on each side by two angular longitudinal and
opposite grooves, which give the tooth a three-lobed configuration.
The centre of this tooth consists of osteo-dentine, which is here harder
than the dentine or the cement. It consequently forms a ridge on the
grinding surface of the tooth, which extends along the middle of its
long axis and sends a prolongation on each side, into each of the tliree
rhomboidal lobes into which the surface is divided. In the phyllophagous
Bruta—the sloths—the teeth which are few in number, are composed of
a large central axis of vaso-dentine, surrounded by a thin investment of
hard dentine, and a thicker covering of cement. They possess the cha-
racters of uninterrupted growth, and implantation by a simple deeply
excavated base, not separated from the exposed portion by a cervix.
Such were the teeth of the extinct Megatherium, the most gigantic of
the sloth tribe. The teeth of the Mega-
Its dental formula was £: f ; .
therium present a more or less tetragonal figure, and the grinding
surface of each is traversed by two transverse angular ridges. The
sloping side of the ridge nearest the centre of the tooth is formed by
vascular dentine, the side farthest from the centre by cement, whilst
the hardest material—the unvascular dentine—forms the summit of the
ridge.
In those of the true Cetacea, which possess true functional teeth e. g.,
the Cachalot, the Dolphins, and Porpoises—these organs, with the single
exception of the common Dolphin before referred to — (note d., p. 61),
are limited to the maxillary and mandibular bones. They, may, there-
fore, be briefly noticed here. In the Cachalot (Physeter macrocephalus),
the visible dentition is confined to the lower jaw it consists, in the
:
male, on each side, of about twenty-seven sub-incurved, conical, or
ovoid teeth. In the female, the teeth are fewer—twenty-three in each