parts of the same individual; some possessed a rudimentary nail on the
great toe, others none at all; but they otherwise present no external
differences on which to establish even varieties of a species.

"Yet, when we examine the crania of these individuals, we find
remarkable differences of form, proportion, and dimension, no two
being exactly alike. The slope of the profile, and the projection of
the muzzle, together with the size of the cranium, offer differences
as decided as those existing between the most strongly marked forms of
the Caucasian and African crania in the human species. The orbits vary
in width and height, the cranial ridge is either single or double,
either much or little developed, and the zygomatic aperture varies
considerably in size. This variation in the proportions of the crania
enables us satisfactorily to explain the marked difference presented
by the single-crested and double-crested skulls, which have been
thought to prove the existence of two large species of Orang. The
external surface of the skull varies considerably in size, as do also
the zygomatic aperture and the temporal muscle: but they bear no
necessary relation to each other, a small muscle often existing with a
large cranial surface, and vice versa. Now those skulls which have the
largest and strongest jaws, and the widest zygomatic aperture, have
the muscles so large that they meet on the crown of the skull, and
deposit the bony ridge which separates them, and which is the highest
in that which has the smallest cranial surface. In those which combine
a large surface with comparatively weak jaws, and small zygomatic
aperture, the muscles, on each side, do not extend to the crown, a
space of from 1 to 2 inches remaining between them, and along their
margins small ridges are formed. Intermediate forms are found, in
which the ridges meet only in the hinder part of the skull. The form
and size of the ridges are therefore independent of age, being