Page:Popular Science Monthly Volume 13.djvu/446

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speed over the ground or trees, but it is an objection where the limbs are to be used as paddles against the air or water. In fact, the more we know of the skeleton and the environment of the animal, the more we see that its variations throughout the animal kingdom are the combined results of the movements of the organism itself and the opposition of the medium in which it moves. Where the actions of the animal are slow, it is found that the bones of the limbs are more rigid and often joined, as shown in the case of the sloth by Prof. Cope. The head and the ends of the limbs, being in constant use against the vital conditions of the environment, are the soonest modified. The bones are formed by the muscles, and the muscles are developed through the movement of the animal. We may all have noticed that, when the skin is stripped off, and the extremities of the backbone, the head and tail, are cut off, together with the feet, the carcass of a cat looks much like that of a rabbit in the same condition.

Those who have not investigated such an instance of similarity, yet know that in a butcher's shop there is a superficial sameness in the appearance of meat which it is the business of a good marketer to see through; while a good many of us, who are unaccustomed to provide, would no doubt be not a little puzzled to distinguish the body of a calf from that of a sheep as it hangs in the stalls. The same thing holds good with the bodies of birds and other animals: a duck is identified most quickly by the webbed feet and flattened bill. Thus it is a matter, perhaps, of general knowledge that an animal is difficult to recognize when the head and extremities of the limbs are missing, and we see now the reason that it is so. We may go even further than this and account for the mistakes of antiquity on the same principle. It is not credible that the head or feet of a mammoth could have been mistaken for those of a man, nor were they as a fact; but a thigh-bone, or rib, offered less difficulty by reason of the greater resemblance. Hence we find that these mistakes have been made with some excuse for their commission. The difference existing between these fossils and the corresponding bone in man was so small as to escape the notice of the anatomists of antiquity. The general resemblance between the skeletons of all vertebrate animals was not then fully appreciated. People distinguished the animals in old times from man by their heads, feet, and fur, to say nothing of their tails; and, when they found an isolated internal bone, they may readily be forgiven for having wrongly referred it.

Again, the bones being produced through the muscles, and these through the nutrition of the animal, there is always a proportion between the skeleton and the stomach and soft parts of the body. The skeleton is a very good index of the comparative bulk of the animal, and this fact assists us when we attempt restorations of extinct species.

From the herd of monkeys found in the Oriental and Ethiopian regions of the Old World, the apes are readily distinguished by certain structural characters. The body is that of a human being, except that