the floor of the cornu--which is, as it were, arched over the roof of
the sulcus. It is as if the groove had been formed by indenting the
floor of the posterior horn from without with a blunt instrument, so
that the floor should rise as a convex eminence. Now this eminence is
what has been termed the 'Hippocampus minor;' the 'Hippocampus major'
being a larger eminence in the floor of the descending cornu. What may
be the functional importance of either of these structures we know not.

As if to demonstrate, by a striking example, the impossibility of
erecting any cerebral barrier between man and the apes, Nature has
provided us, in the latter animals, with an almost complete series of
gradations from brains little higher than that of a Rodent, to brains
little lower than that of Man. 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