Page 46 - My FlipBook

44 MACROSCOPIC ANATOMY OF THE HUMAN TEETH.

isharp antilc with the niorsal surfhcc, whicli is smMiiouiitrd with two
tubercles. Sometimes, but rarely, tlie lingual groove passes over on to
this face.
The mesidi and disfdl faccn (.s) are wide and flattened transversely,
but convex vertically. They are trapezoidal in outline, the morsal
border being longer. The cervical border is more convex, and tlips
toward the neck of the tooth.
The neck (t) is very regular in outline and contour. It is approxi-
matelv square with all four sides depressed in the centres. The mesial
and distal are depressed at the origins of the grooves leading down
upon the roots ; the lingual and buccal are depressed at the bifurca-
tion of the roots, the depression, which is wide and deep, extending up
on to the neck, especially upon the buccal side. The enamel line is
quite irregular, dipping down on the lingual and buccal, and leading
well up on the mesial and distal sides.
The rootM are two in number, placed with their longer diameter trans-
versely to the jaw. They are wide bucco-lingually, and flat and narrow
disto-mesially, being situated distally and mesially to the crown. The
posterior is formed of the two posterior cones, and the anterior of the
two anterior cones {A). This is plainly shown in the formation of the
roots, Avhich are grooved both distally and mesially, and in the tendency
to bifurcation, which sometimes actually occurs. They divide close to
the crown, so that the grooves of bifurcatiou extend well up on the
neck. The distal root is thicker and more rounded than the mesial,
the latter being more flattened, with the grooves deeper, and it is more
often bifurcated. Both are deflected from the median line.
The pulp canal is shaped like the roots, with two main branches.
The distal branch is the larger, being round and open, as the root is more
rounded. The mesial branch is flat and spindle-shaped, being difficult
to enter, and usually having two sub-branches following the buccal and
lingual divisions of the root. These sub-branches are small and hair-
like and troublesome to enter.
The lower second molar (Fig. 25) differs from the first in many
respects. It is of the same general form, but is more quadrangular, as
it has but four tubercles. It is more rounded and symmetrical than the
first, the four cones and four primitive tubercles being well marked.
The absence of the fifth tubercle leads to most of the differences between
the second and the first molar.
The morsal face (c) has but four tubercles, one at each corner of the
face, differing from that of the first molar, which has five. The fifth
tubercle rarely appears in the higher races of mankind, but is some-
times found in the low and savage races, and occurs regularly in the
apes. It is not uncommon in the negro, but is absent as a rule in