until, in the Elephant, the Porpoise, the higher Apes, and Man, the
cerebral surface appears a perfect labyrinth of tortuous foldings.

Where a posterior lobe exists and presents its customary cavity--the
posterior cornu--it commonly happens that a particular sulcus appears
upon the inner and under surface of the lobe, parallel with and beneath
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