These are three brains of different grades, formed alike on the same vesicular plan. The resemblance of the optic lobes to the cerebrum is very striking, and when we open them we see what corresponds to the lateral ventricles of the cerebrum, with a structure at the bottom corresponding in position and character with the inferior ganglion of the cerebrum. The subdivision of function is similar to that of the cerebrum, the anterior portion of these lobes being of an intellectual, perceptive 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]