ch, in the recent state,
is interposed between the cerebrum and cerebellum, and prevents the
former from pressing upon the latter. (See Figure 16.)

This groove, therefore, indicates the line of separation between that
part of the cranial cavity which contains the cerebrum, and that which
contains the cerebellum; and as the brain exactly fills the cavity of
the skull, it is obvious that the relations of these two parts of the
cranial cavity at once informs us of the relations of their contents.
Now in man, in all the old-world, and in all the new-world Simiae,
with one exception, when the face is directed forwards, this line of
attachment of the tentorium, or impression for the lateral sinus, as it
is technically called, is nearly horizontal, and the cerebral chamber
invariably overlaps or projects behind the cerebellar chamber. In the
Howler Monkey or 'Mycetes' (see Figure 16), the line passes obliquely
upwards and backwards, and the cerebral overlap is almost nil; while in
the Lemurs, as in the lower mammals, the line is much more inclined in
the same direction, and the cerebellar chamber projects considerably
beyond the cerebral.

When the gravest errors respecting points so easily settled as
this question respecting the posterior lobes can be authoritatively
propounded, it is no wonder that matters of observation, of no very
complex character, but still requiring a certain amount of care, should
have fared worse. Any one who cannot see the posterior lobe in an ape's
brain is not likely to give a very valuable opinion respecting the
posterior cornu or the hippocampus minor. If a man cannot see a church,
it is preposterous to take his opinion about its altar-piece or painted
window--so that I do not feel bound to enter upon any discussion of
these points, but content myself with assuring the reader that the
posterior cornu and the hippocampus minor, have now been seen--usually,
at least as well developed as in man, and often better--not only in the
Chimpanzee, the Orang, and the Gibbon, but in all the genera of the old
world baboons and monkeys, and in most of the new world forms, including
the Marmosets.* ([Footnote] *See the note at the end of this essay for a
succinct history of the controversy to which allusion is here made.)

(FIGURE 21.--Drawings of the cerebral hemispheres of a Man and of a
Chimpanzee of the same length, in order to show the relative proportions
of the parts: the former taken from a specimen,