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306 fissure, is a very striking feature in the upper aspect of both the Quadrumanous and the human brain; but, in the Chimpanzee, the point of the V is situated a little in front of the transverse axis of the hemispheres, whilst in man it is, to a still greater extent, behind that axis. Suppose the whole length of the hemispheres to be represented by 100, then from the fore-part of the brain to the point of the V, would measure, in the Chimpanzee, 49, and, in man, 57. It is obvious, on further examination, that whereas nearly one-half of the upper surface of the cerebrum lies in front of the fissures of Rolando in man, a very little more than one-third is so placed in the Chimpanzee. In the Orang's brain, figured by Dr. Rolleston, the proportion appears to be mid-way between the two. There can be no reasonable doubt, that the part of the hemispheres situated in front of these remarkable fissures in man, the Orang and the Chimpanzee, and we may add, in still lower Quadrumana, are homologous parts, in the truest sense of that term. The anterior cornua of the lateral ventricles project into them, passing beyond the first ascending convolution on each side. The external perpendicular, or vertical, fissure, figs. 4, 5, V, is particularly well developed in the Chimpanzee's brain; it is not bridged over, on the upper surface of the hemispheres, by any superficial convolutions, so that its posterior border, named by M. Gratiolet the operculum, is smooth and uninterrupted. It is continued, on the internal surface of the hemisphere, as a distinct internal perpendicular fissure. In the particular human brain which we have dissected for the purposes of this paper, the external perpendicular fissure is obliterated, but it can be unmistakeably traced on the internal surface of the hemispheres, within the longitudinal fissure, as the internal perpendicular, or vertical, fissure. In the ape, this fissure cuts off 23 parts, posteriorly, out of 100 of the length of the hemispheres as visible above; in man, the corresponding portion represents 20 parts out of 100; in the Orang figured by Dr. Rolleston, the proportion seems to be intermediate. There can be as little doubt here, as in regard to the parts in front of the fissure of Rolando, that the portions of the hemispheres behind the perpendicular fissure, in man, the Orang, and the Chimpanzee, as well as in the lower apes, are strictly homologous parts of the cerebrum. We shall see that the posterior cornua of the lateral ventricles extend into them. Between the fissure of Rolando on each hemisphere, and the perpendicular fissure, is an equally homologous region which, in the Chimpanzee, occupies the remaining 28 parts out of 100, of the total length of the cerebrum; whilst, in man, it constitutes 23 parts, i. e. as seen directly from above; but this particular region, and also the part behind the perpendicular fissure, it must be remembered, are just those which gain so much in their vertical dimensions, in the human brain. If, in fact, we measure longitudinally over the vertex, the relative spaces occupied by these three regions, which may be distinguished as frontal, parietal and occipital, though they do not exactly coincide with the