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THE MOLARS. 47

t>'pical three molar roots are found. Sometimes there are multiple
roots, which are likely to be curved iu various directions and may
have decided hooks.
In the large conate root, the pulp canals usually coalesce, but in
cases in which the root is divided there will also be division of the
pulp chamber.
The lower third molar is similar to the other loAver molars in
general form (Fig, 27, u), but is probably not so erratic and not subject
to such extreme variations. The crown is
Fig.
quadrangular in section, the angles rounded.
On the morsal face [b), there are four
principal tubercles as in the second molar,
but this may be supplemented by the ex-
tension of the disto-marginal ridge into a
cingule or heel (c). This heel is rather
erratic ; it may be large or small, thus
The lower third mobir.
modifying the size of the morsal sur-
face. Sometimes the face is wrinkled and, like this tooth in the
orang utan, the sulci exhibit the cruciform shape similar to that of the
second molar. The many grooves leading away from the main sulcus may
be imperfect and become the seat of caries. The buccal groove running
from the morsal on to the l)uccal face (a) is very subject to imperfection.
The four lateral faces are similar to those of the second molar, except
that the distal is more convex and full, and often very prominent if the
fifth cingule is well developed.
The neck is of similar shape to that of the second molar.
The roots are similar to those of the other lower molars, but generally
smaller as compared with the crown (cl). They are usually divided like
the others, but the two may be fused together, or be closely opposed.
In either case they are usually projected distally more or less, leading
backward into and under the ramus, thereby rendering extraction of
this tooth difficult and dangerous, especially where the maxilla is of
Fig. 28.

The fourth molar.
dense structure or where there is impaction. The roots are usually
more rounded, especially the distal one, than those of the other molars.
The pulp canah are generally divided, whether the root is or not.