NEUROLOGY. - The brain of the monkey's, of the Old World represents an imperfect outline of the brain of man. By the form and the number of convolutions, LEURET * proved that it approaches to the brain of the human subject ; but however great this analogy may be, there remains, however, no doubt that there are some typical differences between the brain of man and of the monkeys, and that from the Chimpanzee to the Cynocephali, the gradual tendency to inferiority is as manifest as in the other points of organisation. We still want perfect representations of the brain of the first, but we may supply this defect by drawings of the brain of the Orang-alan, of which TIEDEMANN has represented the basis, SANDIFORT the superior surface, and I a ver tical section. (Figs. 125, 126, 127.) If we compare these distinct views of the brain of the Orang-mtan with those of the Baboon represented by LEDRET* (figs. 128,129,130), the inferiority of these to the Orang-cdan is so manifest, that it needs scarcely any further explanation. In the first instance, it appears that the brain of the Cynocephalus, and, ac cording to the observations of TlEDEMANN, we could say the same fbr all the monkeys inferior to the Chimpanzee, the Orang-eetan, and the Gibbons, differs from the brain of man : 1. By a greater breadth in proportion to the length, and consequently by a less elliptical and more triangular form.
2. By less development of the hemispheres of the brain, which do not cover the whole cerebellum.
3. By a smaller number and greater sym metry of the convolutions, and less deep anfractuosities.
4. By less development of the corpus stria tum, thalanzus nervorum opticorum, corpus cal losum, and septunz lueidum.
All these manifestations of inferiority are not so distinct in the brain of the Orang-cetan, which approaches more to that of man. This approximation consists in : I. The more elliptic, and consequently more human-like form of the brain. It is a most interesting fact, that the deviation, in the descending line, begins already in the Gibbons, the brain of which has a more triangular form, and less developed anterior lobes, than the brain of the Orang-cetan.
2. The larger cerebral hemispheres, which are protracted behind the cerebellum.
3. The existence of two separate corpora manzmillaria, which I found also in the Hylo bates leuciscus, and which SANDIFORT repre sented in the Siamang. But they are in these less developed than in the Orang-wtan.
4. The presence of digitations on the cornu Ammonis.
5. More numerous convolutions and deeper anfractuosities.
6. A larger cerebellum.
In all these peculiarities, the brain of the Orang-cetan is superior to that of other mon keys, and still more so to that of the Gibbons, which offer otherwise so much analogy with it. The plate of SANDIFORT, representing the brain of the Siamang, and my dissection of the Hylobates leuciscits, have proved, that in the Gibbons the convolutions are not so numerous; the anfractuosities not so deep, their symmetry greater ; the cerebral hemi spheres less developed ; the cerebellum small er ; the pons VARoLit less distinct ; the cornu Animonis without digitations. This greater perfection of the brain of the Orang-cetan is evidently in accordance with the more eminent intellectual faculties of the Orang-celan, while, according to the observations of DUVAUCEL and of S. MULLER, the Siamang and the other Gibbons are very stupid. But if, on one side, this superiority of the brain of the Orang-wtan, with which the Chimpanzee seems to have a great deal of analogy, cannot be a subject of controversy amongst anatomists, they would however go too far by saying, that the brain of both is in all points similar to that of man. The following differences may be indi cated : I. The mass of the brain, in proportion to the volume of the body, is less in these Apes than in Man.
2. The cerebral hemispheres are less deve loped, and not so much protracted backwards.
3. The nerves are thicker in proportion to the circumference of the brain.
4. The convolutions are not so numerous, and the anfractuosities less deep.
5. The corpus callosum is not so much ex tended backwards.
About the nerves of the Monkeys, I shall but mention one very interesting modifi cation, which I observed in the nervus acces sorius WILusit of the Chimpanzee. It is divided into two branches, as in man, but the internal is not united with the vagus, as it penetrates separately into the larynx. This very peculiar ramification seems to confirm the opinion of BISCHOFF #, that the internal branch of the n. accessorius WILListi forms partly the n. laryngelts superior. About the organs of sense there is not much to say. The eye approaches much to the eye of the hutnan subject, by the existence of the yellow spot on the retina, but it differs by a more thin sclerotica. The ears of the higher order af monkeys resemble much the same organs in the human subject, from which they differ only by a less developed lobulus. The tongue is short, broad, and round, as in man, but it becomes long and narrow in the Inui, and still more so in the Cynocephali.