JAW OF THE GIBBON.
In concluding this part of the subject, which relates especially to the man-shaped Apes, some very obvious reflections occur. There is something very interesting as well as instructive and suggestive in the study of the proportions of the limbs to each other and to the body in the larger Apes, of which the Gorilla is the highest in the scale, and in man. The fingers in man hang down to below the middle of the thigh; in the Gorilla they attain the knee; in the Chimpanzee they reach below the knee; in the Orang they touch the ankle; in the Siamang they reach the sole; and in some Gibbons the whole palm may be applied to the ground without the trunk being bent forward beyond its natural position on the legs. It is also found that in man the arm-bone exceeds in length each of the bones of the fore-arm in a marked manner, and in the Gorilla and Chimpanzee it does so but slightly; the bones are equal in the Orangs, and very unequal in the Gibbons, those of the fore-arm being the longest. When the length of the arms down to the wrist is compared with that of the body, omitting the legs, there is not much difference between man and the Gorilla, but it increases in the Chimpanzee, Orang, and in the Siamang. The lower limbs are short in the Gorilla, and this is characteristic—they offer but a poor support to the huge body—and the resemblance to the symmetrical proportion of the legs to the body in man is scanty indeed. This disproportion is greater in the Chimpanzee and Orangs, in which the lower limbs are pigmies.
Consider the hand in the same manner. Man’s perfect hand, writes Owen, is one of his peculiar physical characters, and that perfection is mainly due to the differences of the first and the other four fingers, and the ability of this first to be opposed to them, as a perfect thumb. A partially opposable thumb, that is to say, one which can be brought over the palm, more or less, is present in the hand of the great Apes. It is large in the Gorilla, so far as Apes are concerned, and it reaches, when it and the fingers are stretched out, to just a little beyond the first joint of the first finger, or rather of its first movable part. But in the Chimpanzee and Orang it does not reach to the joint, and it is longest and strongest in proportion in the Gibbons (Hylobates). In the Gorilla and the Chimpanzee, the wrist-bones are eight in number, but there are nine in the Orangs and Gibbons.
BACK OF JAW OF THE AGILE GIBBON.
The toe-thumb is about five-twelfths of the length of the whole foot in the Gorilla, and it is slightly longer in the Chimpanzee and Hylobates, but it is not more than a fourth of the length of the foot in Orangs.
The nails of all the fingers and toes of the great Apes are flattened, except in the Hylobates, whose thumb and toe-thumb nails only are so; the rest are more claw-like.
Finally, as regards the brain and nervous system. In the man-shaped Apes the brain is smaller as compared with the nerves which proceed from it than in man; and the brain proper is smaller relatively to the cerebellum than in man. The convolutions, the fissures, and eminences of the brain are generally less complex, and those of the two sides or hemispheres of the brain are more symmetrical than in man. The sides of the brain or the hemispheres are rounder and deeper in man, and the proportions of their lobes to one another are different. Some convolutions and fissures present in man are less perfectly formed, but still exist in the Apes, and the cerebellum is not covered entirely in the Hylobates, but it is in the other Anthropomorpha.