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THE MOLARS. 43

The morsal surface {B) is trapezoidal in outline, the buccal line
being the longest. The buccal angles are acute, while the lingual
are rounded and obtuse.
There are five tubercles, two on the lingual margin and three on the
buccal. They are named the mesio-buccal (c), median buccal {d), disto-
buccal {e), disto-lingual and mesio-lingual {g). These tubercles are
(/),
less obtuse and more rounded than those of the other grinding teeth, the
mesio-buccal usually being the largest, the others are not so prominent,
rarely raised and sharp.
The ri(lf/es are : the marginal ridges—buccal, distal, lingual, and
mesial—and the five triangular ridges descending from the five tuber-
cles toward the centre of the tooth.
The grooves and sulci upon the morsal surface are very irregular. A
deep sulcus traverses the face from the mesial to the distal marginal
ridge. A groove runs off toward the lingual side, dividing the lingual
cusps (i), sometimes cutting the lingual marginal ridge, but rarely
reaching over on the lingual face. A groove runs toward the buccal
side, dividing the mesio-buccal from the median tubercle (/), cutting
the marginal ridge and extending over quite on to the buccal face. This
groove often becomes the seat of caries owing to the enamel structure
being faulty. Another groove extends toward the disto-buccal angle (^k),
dividing the median from the disto-buccal tubercle, and rarely extends
over on to the buccal face. A groove may extend distally cutting the
distal marginal ridge (l), and one mesially cutting the mesial marginal
ridge (/»), but these are not usually marked. The triangular groove run-
ning up on each side of the triangular ridges («) divides these from the
marginal ridges. Supplemental grooves may divide the triangular ridges
again. The pits at either end of the sulcus may become the seat of caries
through faulty formation.
The buccalface (C) is an irregular trapezoid in form, the morsal margin
being longest ; the mesial and distal sides converge toward the cervical
border, which is rounded. The morsal margin is broken by the three
tubercles rising upon it. The buccal face is convex in all directions,
that from the morsal to the cervical borders being the most marked
owing to the morsal half converging toward the centre of the tooth.
The buccal groove (o) leading over from the morsal face, divides the
face into two lobes which are full and rounded. Sometimes the disto-
buccal groove cuts off another lobe, thus making three lobes on the buccal
face. These grooves sometimes lead to the cervical border, but usually
terminate in the mi of caries through faulty formation of the enamel.
The Ungual face (d) is wide, rounded, smooth and convex, rather
straight perpendicularly, leaning in the lingual direction. It forms a