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OF THE GRINDERS. 93
round, and have but one cavity. Two of them are placed near
each other perpendicularly, over the outside of the Tooth ; and
the other, which generally is the largest, stands at a greater

oblique ridge just mentioned, gives a sigmoid character to the eminences
on the grinding surfaces of these teeth. In the last true molar, which is
the smallest of the series, the two inner tubercles are blended together ;
and, in many instances, a groove extends at right angles from the one
separating the two outer cusps to the middle of the posterior border of
the grinding surface. The upper molars in Man are implanted by three
diverging fangs, two external and one internal ; but not unfrequently,
in the second molar, the two external are found parallel, and occasion-
ally connate. In the third upper molar, the two external fangs are
more commonly connate, and sometimes, also, the inner fang is blended
with them. Owing to the slow accession of maturity in Man, and the
long interval which elapses between the acquirement of the first and
last true molars, the former tooth is found more worn in proportion to
the other teeth of the same series, than in the Chimpanzees and Orangs.
In the lower jaw, the human molar is quinque-cuspid, the fifth tubercle
being developed posteriorly, and connected with the postero-external
cusp. The fifth cusp is, however, frequently absent in the second tooth
of the series, and is most developed in the dens sapiential. A crucial
depression separates and defines the four principal cusps, and, by a
bifurcation of its posterior branch, includes the fifth. This bifurcation
is most apparent in the third molar. As in the upper jaw, the last
named tooth is the smallest of the true grinders. Each molar is im-
planted by an anterior and a posterior sub-compressed fang, which are
grooved along their opposed side. It is not uncommon to find these
fangs more or less connate in the second and third teeth of the series.
On turning to the genus Troglodytes, the first thing which attracts notice
is the straight line which the grinding series forms in the Chimpanzee
and Gorilla, contrasting strongly with the well-marked curve which the
molar teeth describe in the human subject. In the upper jaw, indeed,
in these great Apes, the line of grinders makes a slight inclination in the
opposite direction to that described by them in Man. Another difference
is the smaller relative size of the grinders as compared with the incisors.
In this last particular, the Gorilla makes a nearer approach to Man than
the Chimpanzee ; for in the former the molars are larger relatively,
when compared with the incisors, than in TV. niger. In the upper jaw,
the first two molars, both in TV. Gorilla and TV. niger, correspond with
the same teeth in the human subject, in being quadricuspid, and in
having the inner anterior and outer posterior tubercles connected by a
low ridge. The sigmoid character thus given to the eminences on the
unworn surfaces of these teeth, is highly indicative of the high position
in relation to Man occupied by the Chimpanzees above the Orangs and
M