Page:Natural History Review (1861).djvu/315

Rh Schroeder van der Kolk's and Vrolik's corresponding view, in both of which the characters of the lateral aspect of the Chimpanzee's brain are entirely lost; the cerebellum and medulla are pressed horizontally backwards, so that the former is tilted up and projects too far behind, and converts the naturally concave lower border of the cerebrum, from the middle lobe backwards, into an even oblique line. The same criticism must apply, we think, to the lateral view of the Orang's brain, given by Dr. Rolleston, the obliquity which he notices in his paper (p. 206) being evidently the result of displacement from pressure.

The comparison of the Chimpanzee's brain, as seen in front and behind, with the human brain, does little more than confirm the observations already made. Anteriorly, in the ape, the want of depth and width of the frontal region, and the hollowing of the orbital surfaces; and, posteriorly, the want of height in proportion to the width, and the smoothing down of the parietal regions, as contrasted with the towering height and width of those parts in man, are chiefly noticeable; so that the Chimpanzee's brain has a more compact, rounded, form. We do not observe, in this animal, the wall-sided shape of the lateral regions, mentioned by Dr. Rolleston as characteristic of the Orang, the sides of the cerebrum being very evenly convex. In the posterior view, the cerebellum of the Chimpanzee appears very wide in proportion to the cerebrum; but it is shallow and less full and rounded, than in man; it is distinctly overlapped by the cerebral hemispheres, on each side, but rather less so, than in the human brain.

On the base of the Chimpanzee's brain, (see figs. 1 and 2,) the deficient length and width, and the pointed character of the frontal region, anteriorly, as compared with man's, are very evident: the orbital surfaces are extremely concave, and the median ridge, on each side of the longitudinal fissure, disproportionately prominent. The under surfaces of the cerebral hemispheres, from the point of the middle lobes to the hinder extremities of the cerebrum, are relatively shorter, and appear more incurved, or kidney-shaped, than in the human brain. The line of greatest width of the base of the brain, in the Chimpanzee, is half an inch nearer to the posterior, than to the anterior end of the hemispheres, lies just in front of the widest part of the cerebellum, and passes across just behind the pons Varolii; whereas in man, it is placed proportionately further back, namely, 1$1⁄2$ inch nearer to the occipital, than to the frontal, extremity, lies considerably in front of the widest part of the cerebellum, and passes across a little behind the pons. The cerebellum itself appears flatter, and is much wider, in proportion to its length, from before backwards, and also, in proportion to the extreme width of the cerebrum, in the Chimpanzee, than in man, in whom it is more protuberant, and though absolutely wider, less so in proportion to its other dimensions, or to the width of the cerebrum. The greater relative size of the cerebellum in this ape, depends therefore, mainly, on its greater