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THE BICUSPIDS. 35

upon its inner face. This cusp is really a cingule, for it is rarely raised
to the full height of a cusp.
It varies much in size from a mere point on the basal ridge (6) on
through various degrees of development, up to a full cusp as large as
the buccal cusp, when the tooth becomes a true bicuspid. The tooth is
therefore essentially a primitive unicuspid premolar, of the form of this
tooth in some of the lower primates.
The buccal face (c) is caniniform, or a long oval in
' outline with
the cusp rising as an abrupt point above it. The angle of the junc-
tion of the marginal ridges may stand out prominently. The face

The lower first bicuspid.
curves markedly toward the lingual side, so that the buccal cusp becomes
central to the long axis of the tooth (a). The cervical border is rounded
at its margin and convex from side to side. The lobes are not marked.
The Ungual face {d) is convex from side to side and straight vertically,
but is not perpendicular, as it is directed toward the lingual side. Its
height depends upon the height of the lingual cingule, which varies from
a mere buccal ridge through various degrees up to the full-sized cusp.
The mesial and distal surfaces are of similar form, convex from side
to side {a, h) slightly flattened at the cervical border and flaring out to
meet the full marginal ridges, which are round and prominent. The
prominence of these ridges and the inward inclination of the lingual
face gives the crown a decided bell shape, tapering to the neck (r/).
The morsal surface (e) is peculiar and difl'ers from every other tooth
in its great variability and the extremes which it may present, from
being a full bicuspid to a mere canine. This face is nearly circular in
outline, the widening of the lateral surfaces by the spreading of the
marginal ridges (/, /) adding to the width. The buccal cusp (g) is large
and prominent, and is also drawn toward the centre of the tooth to
accommodate the occlusion. Sometimes it is high and sharp when the
lingual cusp is reduced, and is low and blunt when the latter is en-
larged,—appearing to have an inverse ratio in size to the inner cusp.
The lingual tubercle or cingule varies much in size, from a mere point
on the liasal ridge, above the cervical border, to a pronounced cingule,
a larger cingule, a small cusp, then a full cusp, the basal ridge (h)