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84 HUNTER ON THE TEETH. —

do not stand so near the outer edge of the Tooth, as the inner
so that the body of the Tooth
do on the inside ; swells out
more from the points, or is more convex, on the outside. The
body towards its neck becomes but very little smaller, and
single roots ; they are conical, sharp, slightly recurved, and compressed
laterally. A fragment of the under jaw of the Zeuglodon has been
figured by Dr Cams, in which a worn-out deciduous molar, is apparently
displaced and succeeded vertically by a premolar. This would indicate
an affinity to the Sirenia rather than to the true Cetacea. For the latter,
like the Bruta, are monophyodonts.
In the Aquatic Pachyderms {Sirenia) known also as Herbivorous
Cetacea, we find molars distinguished by configuration and position.
The number of these teeth in the Australian Dugong does not exceed
twenty-four. In the Malayan species, there are not more than twenty
viz., five on each side in each jaw. But the entire series is never in use
together, the first is sbed before the last has cut the gum. They increase
in size from before backwards. The four first teeth are more or less
cylindrical in figure ; each is implanted by a single fang, which, in its
turn, becomes completed and solidified by the contraction and oblitera-
tion of the basal cavity. The fifth or hindmost molar is more complex.
A transverse section of its crown presents an approach to the hour-glass
configuration of the posterior teeth in the Zeuglodon. The root shows
a tendency to division, whilst the pulp is maintained in a wide basal
pulp cavity, to supply the waste of the crown. In the American
Manatee the formula of the molar series is V° '. V° — 38, but these teeth
'.
are never all in place and use at the same time. In the upper jaw the
first two are shed before the last two appear ; in the lower, seven are
usually in use simultaneously. The first molar, in both jaws, is small
and simple. Beyond the second, the crowns of the upper series are
square ; the grinding surface supports two transverse ridges, each of
which is surmounted by three tubercles ; it is also bounded by an
anterior and posterior basal ridge. Each upper molar is implanted by
three diverging roots, two on the outer, and one on the inner side. The
crowns of the four or five anterior lower molars resemble those above
;
the remainder present a large posterior tubercle ; they are implanted by
two fangs, which enlarge towards the extremity, where they bifurcate.
The grinders of the Manatee not succeeding deciduous teeth, are all
referable to the true molar series. They consist of dentine, with a
general investment of cement, and a coronal coating of enamel. The
large number of the molar teeth, and the simple conical character of
the first tooth which is separated by an interval from the two-ridged
molars, are indications of affinity to the cetaceous character, whilst the
shedding of the anterior teeth before the development of the posterior
—a circumstance presenting an analogy to the mode of succession