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410 DENTAL ANATOMY.

about their succession that it is impossible to say Avhether there are
mohirs and premolars represented or not. The teeth of the upper series
are lodged in the maxillary bones, and begin at a considerable distance
behind the maxillo-premaxillary suture. They progressively increase
in size up to the fifth or sixth tooth, the last being quite small. They
are not in contact with each other, but are separated by slight spaces
about equal to the width of a tooth. The teeth of the lower jaw are
similar to those of the upper jaw in size and shape, Avitli the exception
of the last, which is much larger than the corresponding tooth above.
The teeth of the inferior series close in the intervals between those of
the upper and conversely, causing the summits of the crowns to wear,
as Prof. Owen puts it, ** into two facets divided by a median transverse
ridge." The form of the working surface of the tooth is therefore
wedge-shaped. The first two teeth of the lower jaw shut in front of
the first tooth above, and the last three teeth above behind the last one
of the lower series, leaving them with little or no opposition. Each
tooth continues its cylindriform shape to the bottom of the alveolus in
which it is implanted, having its base excavated into a large pulp-
cavity. It consists of dentine and cementum only.
In another species, the nine-banded armadillo, the number and form
of the teeth are the same. The teeth of this animal, as has already been
stated, have a successional set. According to the definition laid down
for premolar and molar teeth in the diphyodont Mammalia generallv,
there would be one molar and six pi'cmolars in the dentition of this
animal. The rooted appearance of the deciduous teeth, according to
Tomes, is not due to the possession of true roots, but to the absorp-
tion set up by the approach of the successors.
The genus Priodon of this group has as many as one hundred teeth,
the greatest number exhibited by any land mammal. Thev are rela-
tively small and simple in form, and are confined to the maxillary and
mandibular bones. They vary in number from twenty-four to twenty-
six upon each side in the upper, and from twenty-two to twenty-four
upon each side in the lower jaw. In the living genus Dasi/pus there is
one tooth upon each side implanted in the premaxillary bone, which,
according to the definition, becomes an incisor, while in still another
extinct genus, Cli/ami/fJofhcrium, almost equalling in size the rhinoceros,
there were two incisors above and three which oj^posed them below. In
GlijpfofJon the teeth are more complex in pattern, being laterally com-
pressed and divided by two vertical grooves upon each side, which are
opposite to each other. The resulting structure from this arrangement
is three transverse vertical plates connected in the centre by an isthmus.
There were teeth in the premaxillaries in this genus.
The megatheroids affV)rd another example of moderate complexity in
the enamelless teeth of the Brufa. In the gigantic extinct Megatherium
there are five molars above and four l)elow u})on each side. They are
very deeply implanted in tiie substance of the jaw bones, and have
remarkably elongated pulp-cavities, which communicate with the grind-
ing surface by means of a narrow fissure. The pulp-cavity is inmie-
diately surrounded by soft, more or less vascular dentine-^the vaso-
dentine of Owen—which is covered by a thin layer of unvascular, much