And it is a remarkable circumstance
that though, so far as our present knowledge extends, there 'is' one
true structural break in the series of forms of Simian brains, this
hiatus does not lie between Man and the man-like apes, but between the
lower and the lowest Simians; or, in other words, between the old and
new world apes and monkeys, and the Lemurs. Every Lemur which has yet
been examined, in fact, has its cerebellum partially visible from
above, and its posterior lobe, with the contained posterior cornu and
hippocampus minor, more or less rudimentary. Every Marmoset, American
monkey, old-world monkey, Baboon, or Man-like ape, on the contrary, has
its cerebellum entirely hidden, posteriorly, by the cerebral lobes, and
possesses a large posterior cornu, with a well-developed hippocampus
minor.
FIG. 20.--Drawings of the internal casts of a Man's and of a
Chimpanzee's skull, of the same absolute length, and placed in
corresponding positions. 'A'. Cerebrum; 'B'. Cerebellum. The former
drawing is taken from a cast in the Museum of the Royal College of
Surgeons, the latter from the photograph of the cast of a Chimpanzee's
skull, which illustrates the paper by Mr.
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