In its place in
the brain it is like a book in a library; and as the book offers on
its back a title expressive of its contents, so we label each
convolution with its proper title.

In addition to the folding process, a complex growth of fibres uniting
in the corpus callosum completes the solidification, but not so
thoroughly as to prevent our reopening and spreading out the
convolutions by exercising a little dexterity. This was a puzzle to
some of the anatomists in the time of Gall, but I have found no
difficulty in opening out the convolutions to the extent of five or
six inches square. The cerebellum, too, though its ventricle is
obliterated, is susceptible also of a manipulation, showing that it
has some traces of its original formation.

From the twelve weeks embryo to those of twenty-one weeks and of seven
months we trace a progressive development and a commencement of the
furrows that form the convolutions.

Thus we perceive in the essential plan of the brain its two organs,
cerebrum and cerebellum, are hollow spheres which grow gradually into
solid bodies, filling their interior cavities, of which the lateral
ventricles in the cerebrum, which have been explained, are the
remnants.

The great importance of these anatomical details arises from the fact
that they show us the true central region of the brain from which its
development must be determined; and although this work, designed for
the general reader, cannot say much of the brain, it is necessary to
show its true conformation to enable us to estimate the living brain
correctly, so as to describe accurately living men, study the forms of
crania, and derive some profit in ethnological studies from the forms
of crania which to the ethnologists of the present time are of very
little value or significance, since they neither have nor claim a
knowledge of the psychic functions of the brain. I trust, therefore,
my readers will not neglect these anatomical memoranda, which they
will find very valuable.

[Illustration: 21 Weeks 7 Months;
In the brain of seven months, the right hemisphere is out open
horizontally, showing the ventricle.]

I am not aware that any anatomical, physiological, or phrenological
writer has given the exposition of the principles of cerebral
development which I have been presenting for nearly half a century,
although the anatomical facts are patent to all who choose to examine
cerebral embryology, and think of what dissection reveal