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OF THE (J HINDERS. 91
There is a greater difference between these Grinders in the
Upper and Lower-Jaw, than any of the other Teeth. In the
Upper-Jaw they are rather rhomboidal, than square in their

tinct analogy to the Rodent order in the configuration of the incisors,
there are four teeth in the molar scries on each side above, and three
below ; they are implanted vertically, and in parallel lint s. The molars
are simple in structure, coated with enamel, and they have a flat sub-
elliptic, grinding surface. In the upper jaw, the first is the smallest,
and the second the largest, in the series. The first and last have each
one root, the second and third each three roots. In the lower jaw, the
inequality in size is less than in the upper, but the third is the smallest.
The first lower molar has two roots, the second and third have each one.
The molar series in the genera Stenops and Lemur consists of six teeth
on each side in both jaws. The three anterior are premolars. In the
true Lemurs, the premolars have the outer part of the crown produced
into a pointed lobe ; the inner forms a tubercle, which is largest in the
second and third. The true molars have the inner division of the
crown so increased as to give it a quadrate form ; the outer division is
divided into two pointed lobes. The first true molar is the largest,
above and below. The Monkeys of the New World (Platyrhynce) mani-
fest their affinity to the Lemurs in the number of the premolars, which
is three on each side of both jaws. The small Marmozets have the true
molar series on each side, above and below, reduced to two.
The Catarhine Quadrumana of the Old World have the same number
of premolars and molars as Man. We shall again best illustrate the
peculiarities of the Human molar dentition, by comparing it with the
grinding series in the highest Apes. The characteristics of the Human
premolars have been already described {vide Notes k and Z, pp. 78 and
79). If we contrast with the human premolars the same teeth in the
genus Troglodytes, we notice that, in the upper jaw, the premolars
of the Gorilla and Chimpanzee are bicuspid, as in Man ; but they are
larger than the human, and they differ in several other important
particulars. The external cusp of the first premolar, in both species of
Troglodytes, is larger than the inner ; in the second premolar, the inner
is larger than the outer ; in Man, the external is the larger in both.
This alternation in the size of the cusps of the premolars of the Chim-
panzees corresponds with, and contributes to, the straight line formed
by the whole grinding series ; whilst the great size of the external cusp
gives to the first premolar, when viewed from without, the appearance
of being greatly superior in size to the second. Each premolar in
Troglodytes is implanted, like the true molars, by three divergent fangs,
two external and one internal, which at their ends curves towards each
other. Professor Owen states that, in one female skull of Tr. niger
which he examined, the two external fangs of the second premolar are