Page:Popular Science Monthly Volume 33.djvu/847

Rh of prehension, but they are at the same time organs of locomotion; the hinder limbs are also adapted to walking, but they are at the same time organs of prehension. With the lemurs there are also the same general types of all the limbs, for prehension in front, for walking behind, but the fore extremity is in fact more a paw, and the hinder one more a hand by comparison; witness, for example, the Cheiromys. Other monkeys are as quadrupedal as they are quadrumanous. Consider the three upper segments of each limb: there are indeed an arm in front and a leg behind; but look only at the last segment, and it will be found to be, in front as well as behind, a hand in its principal characteristics, the separated and opposable thumb, and the nails.

With man, the harmony is perfect, because the functions are specialized, and the organs are all adapted in the same respective directions, the fore ones for prehension, the hinder ones for walking. Beyond our branch of the primates, looking toward its origin, the four limbs all exhibit themselves with the same types, but less affirmed, less precise: all four for prehension, the fore ones more so; all four for walking, the hinder ones more so. The evolution begins after the train of the marsupials, and specializations are made in different directions. With some, as the galeopitheci and the cheiropterschiropters [sic], the particular adaptation took the direction of flight; a part or all of the limb was not transformed, but bent itself to what was required, was obedient to solicitations. With others, as the ungulates, the adaptation took the direction of an exclusive locomotion upon all four limbs. These became gradually modeled upon the same type, the useless bones disappeared or were fused, and some superfluous motions ceased, while others became accentuated, and the necessary corresponding anatomical dispositions with them. With others, as the carnivora, which were to run on the ground to reach their prey, while they must be able at the same time to seize, hold, and tear it, the four paws remained perfect locomotor organs, but at the same time also organs of attack by their claws, and to a certain measure, particularly in the fore extremities, organs of prehension. An adaptation of another kind was produced with the monkeys. The animals from which they sprung dwelt in trees and ran along the branches. They needed to increase their power of prehension, they had to clasp the rounded trunks of trees, to hook on to branches in passing from one to another. The adaptation seems to have appeared first in the hinder limbs, and then in the fore-limbs. The whole of the limb did not have to lose its peculiar type for that; but it was enough if the extremities were in some way fitted to it. Nature was contented with nails, separated and opposable thumbs, and more flexible fingers, without going up to the next segment.