Page:Natural History Review (1861).djvu/320

308 usually be recognized in the human brain, by tracing outwards from the longitudinal fissure, the internal vertical fissure, which is always present, though thrust backwards at its upper end by the enlargement of the parietal lobe, so as to be somewhat oblique instead of vertical. On the internal surface of the hemispheres of the Chimpanzee, the fronto-parietal and quadrate lobes are seen to occupy the space in front of this fissure, a small internal occipital lobule lies behind it, and the temporo-occipital lobe is at once distinguishable, below the anterior portion of the fissure of the hippocampus. As thus defined, it is impossible to escape from the conviction that all the above-named parts exist in the Chimpanzee, as well as in man; and that, amongst others, the little occipital lobules at the posterior extremity of each hemisphere, in the former, are the homologues of those in the latter. We shall see that this conclusion is fully supported by the closest scrutiny of the convolutions, and of the internal structure of the cerebrum.

As to the convolutions in the Chimpanzee's brain, one can hardly pay a better tribute to M. Gratiolet's general accuracy, than to adopt his description of them, whilst referring to our own specimen. After pointing out the general characters of the frontal, parietal and occipital lobes, a remarkable notch which interrupts the border of the orbital surface, (seen in our fig. 4), the large size of the occipital or posterior lobe, and the even or perfect edge of its operculum, figs. 4, 5, in front of 10,10′, he proceeds thus, p. 50:—

"The convolutions of the frontal lobe are very large, even larger and wider than those of the Orang. The superior frontal convolution (figs. 3, 3′, 4 and 5,) is subdivided into two parts, of which the highest is marked by secondary sulci.

"The middle frontal convolution, 2, is well marked. The inferior frontal or supraciliary convolution, 1,1, is very large, and broadly designed, so that the frontal lobe is well developed in all its parts.

"The first ascending convolution, 4,4, is slender, flexuous, and only slightly inclined backwards: it presents no marginal notches, and its surface is absolutely smooth.

"The second ascending convolution, 5,5, is equally simple and smooth; it passes up by the side of the preceding one, forming parallel flexuosities with it; but having reached above the bent convolution, 6, (pli courbe), it forms an elbow, and spreads out into a large lobule, 5′5″, which is prolonged back to the external perpendicular fissure. This lobule, [named by M. Gratiolet the lobule of the second ascending convolution] is very elegantly subdivided by a rather complicated sulcus, which serves to separate two distinct convolutions, one external, 5′, the other internal, 5″. The external convolution pursues a very simple course; but the internal one is folded several times upon itself, an arrangement which is tolerably constant.

"The commencement of the bent convolution (pli courbe), 6,6′, is remarkable. In the Orang and in the Gibbon, it begins at the top of the Sylvian fissure. In the Chimpanzee, it arises in front of the summit of that fissure by a large extremity, fig. 4, and describes a very extensive curve around it.

"As to the descending part, 6′, of the bent convolution, it is very slender, scarcely flexuous, and rather long, * * * *

"The convolutions of the temporal lobe, are very simple, * * * * . [They are