id of excessively developed
supraciliary prominences as a Man's, though some varieties exhibit great
crests elsewhere (See pp. 231, 232); and in some of the Cebine apes and
in the 'Chrysothrix', the cranium is as smooth and rounded as that of
Man himself.

What is true of these leading characteristics of the skull, holds good,
as may be imagined, of all minor features; so that for every constant
difference between the Gorilla's skull and the Man's, a similar constant
difference of the same order (that is to say, consisting in excess or
defect of the same quality) may be found between the Gorilla's skull
and that of some other ape. So that, for the skull, no less than for the
skeleton in general, the proposition holds good, that the differences
between Man and the Gorilla are of smaller value than those between the
Gorilla and some other Apes.

In connection with the skull, I may speak of the teeth--organs which
have a peculiar classificatory value, and whose resemblances and
differences of number, form, and succession, taken as a whole, are
usually regarded as more trustworthy indicators of affinity than any
others.

[Illustration: FIG. 17.--Lateral views, of the same length, of the upper
jaws of various Primates. 'i', incisors; 'c', canines' 'pm', premolars;
'm', molars. A line is drawn through the first molar of Man, 'Gorilla',
'Cynocephalus', and 'Cebus', and the grinding surface of the second
molar is shown in each, its anterior and internal angle being just above
the 'm' of 'm2'.]

Man is provided with two sets of teeth--milk teeth and permanent teeth.
The former consist of four incisors, or cutting teeth; two canines, or
eyeteeth; and four molars, or grinders, in each jaw--making twenty in
all. The latter (Fig. 17) comprise four incisors, two canines, four
small grinders, called premolars or false molars, and six large
grinders, or true molars, in each jaw--making thirty-two in all. The
internal incisors are larger than the external pair, in the upper jaw,
smaller than the external pair, in the lower jaw. The crowns of the
upper molars exhibit four cusps, or blunt-pointed elevations, and a
ridge crosses the crown obliquely, from the inner, anterior cusp to the
outer, posterior cusp (Fig. 17 m2). The anterior lower molars have five
cusps, three external and two internal. The premolars have two cusps,
one internal and one external, of which the outer is the higher.

In all these respects the dentition of the G