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THE MOLARS. 39

The upper first molar approximates the secoud bicuspid on its distal
side. There is a marked and abrupt change in form, as the molar has
double the number of cusps of the bicuspid,—being formed like two
bicuspids fused together. The four tubercles mean an extension of sur-
face and a further adaptation to functional requirements. The crown
is laro-e and cubical in form, and more or less rounded.

Fig. 21.

Architectural diagram.

The upper molar.

The buccal face (K) is wide and rounded. It is twice the width of
the bicuspids. It is broadest at the morsal margin, narrowing upward to
the cervix, where it is widely rounded or arched. A vertical depression,
the buccal groove (l), extends from the cervical border to the morsal
margin, dividing the face into two oblong rounded eminences, the mesial
and distal buccal lobes (m m).
The lingual face (n) is more rounded than the buccal, the cervical por-
tion being the most convex (o), the mesial and distal sides being depressed
toward the single lingual root. The morsal half is divided by the
lingual groove which descends over the lingual marginal ridge be-
(q),
tween two lobes, the mesial (r) and distal (jj), which are usually much
rounded. The morsal half of the face curves toward the grinding sur-
face. The mesial lobe sometimes presents the lingual cingule (s), a
sort of fifth tubercle of greater or less size. A groove branches from
the lingual groove and extends over, between the cingule and crown.
The mesialface (T) is flat longitudinally, descending from the marginal
ridge to the cervix in a nearly straight line. Bucco-lingually it is