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32 MACROSCOPIC ANATOMV OF THh' HUMAN TKKTIi. —

Tli(> roof is long:, iiattencd, and tapering [a, b, c). It is shdrtcr tlum
that ot'the up])or canine. It is grooved on tlie mesial and distal sides,
so niueh so as to tend toward bifurcation. This, indeed, sometimes hap-
])ens in man, thereby recalling the ibrm usual to the primates and some
other lower animals.
T\w jjtt/jj c((ii(i/ \i^ of the same general I'onii as the root, often ])re-
senting the spindle shape on section. It is somew hat dilVieult to enter
on acconnt of its flattened sha})e and narrowed channel.

The Bicuspids.
12. The Upper Bicuspids,—The npper bicuspid is formed bv duplica-
tion of the primitive cone and cusp in a transverse direction (Fig. 17, a).
Viewed from the standpoint of com-
l)arative dental anatomy, the external
cone is the canine cone—and to this is
added the internal or bicuspkl cone, the
tooth being a donble canine. The bi-
cuspids are the first of the complex
teeth. The internal cusp is formed
by the raising of the inner primitive
The upper bicuspids.
cusp of the canine and the develop-
nient of a root to snpport it. The distinctive featiu'c of the architec-
ture, therefore, is its formation from two cones, and this makes it a
weak tooth as regards its mechanical structure and resistance to mas-
tication, for the binding of the bases of the cones and cusps depends
upon the connecting power of the two marginal ridges (6, h), and when
these are destroyed the cones readily part and split off.
The bicuspids in man are homologous with the premolars of the
quadrumana and other lower mammals. They succeed and displace the
molars or grinders of the deciduous set. They are placed next after the
canines in both jaws, and midway between the cutting and grinding teeth.
Their function is the crushing of food preparatory to mastication.
The upper first bicuspid approximates the canine on the distal side.
The buccal face (c) is of spear-head shape, similar to that of the
canine. This is more apparent in some lower mammals than in man, in
whom it is much reduced and rounded, so as to give usually the a])])ear-
ance of a long, rounded oval. The buccal cusp (c) rises sharply and
prominently from the lower centre of the face, from which a strong ridge
{(T) leads up to the cervical border. The mesial and distal lobes {e, e) are
rarely conspicuous, and the furrows between them and the central ridge
lead but half way up the crown. The lobes sometimes have prominent
points at the morsal margins which in lower mammals become pro-