ve character, and the posterior the seat of the
impulses. This has been demonstrated also in the experiments of
vivisectors, in which the irritation of the posterior part has
produced a vocal utterance or bark. Spurzheim gives a view of the
brain of the pike with an optic lobe partially opened, to show the
ventricle.

The cerebellum or physiological brain is formed on the same general
plan, having its energetic or forcible functions in the posterior
inferior regions, and its more sensitive functions located anteriorly.

In the embryo of twelve weeks a great advance has taken place; the
optic lobes or quadrigemina are still large, but the cerebrum is
larger than all the remainder. Still, it has not yet developed what
might be called frontal and occipital lobes. The basis of the middle
lobe, which is the most physiological portion of the cerebrum, being
devoted to the sensibility, appetites, and muscular impulses, is that
which first presents itself, being the first outgrowth from the great
inferior ganglion or summit of the spinal system. As human brains
degenerate to a lower type they approximate this form. The frontal and
occipital lobes dwindle and the principal mass remaining is that in
the basis of the skull between the ears. We see this form distinctly
in congenital idiots. The embryo cerebrum here represented measures
but three lines vertically, four lines in length, and five lines in
thickness. (The line is the twelfth of an inch.) The nerve membrane of
this hollow cerebrum is barely a fourth of a line thick. The
cerebellum, formed in the same way by projection from the summit of
the spinal cord, making two leaves that come together on the median
line, has also a cavity contained between them, and just behind the
medulla oblongata, which is finally reduced to the little space called
the fourth ventricle, when the cerebellum grows to become a solid
body.

[Illustration: 12 Weeks]

The growth of the cerebrum and cerebellum into solid bodies instead of
vesicles is effected by the folding together of the primitive membrane
as furrows appear upon its surface, by which it is changed into folds
or convolutions, each of which (like the fold of a ruffle) may be cut
out from its neighbors and opened from its inner side, like a book. It
resembles a book also in the fact that it contains innumerable ideas
or psychic elements, and the psychometer might read from each
convolution as a book the impressions recorded in it.