For there is a very
marked groove in every such skull, as in the human skull--which
indicates the line of attachment of what is termed the 'tentorium'--a
sort of parchment-like shelf, or partition, which, in the recent state,
is interposed between the cerebrum and cerebellum, and prevents the
former from pressing upon the latter. (See Fig. 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 Fig. 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.
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