Page:Popular Science Monthly Volume 34.djvu/210

198 their ornamental manes and their proud and stately gait and carriage. All these points are wholly wanting in the clumsy llama and alpaca group. Stranded remnants, as it were, of the Eocene world, those antique creatures linger on among their mountain valleys a perpetual milestone by whose indications we may mark the progress since effected, under stress of selective agencies, in the main advancing body of the higher ruminants.

On such a simple original type, defenseless and ungainly, the camel is a specialized and adapted desert variation. The undeveloped llamas have no humps, and they have their two toes quite separated in a certain awkward, ungraceful, splay-footed fashion. In the true camels, on the other hand, the two toes are united below by a kind of horny sole, almost to their points, which terminate in a couple of small hoofs, and beneath the foot there is a soft cushion, by which the instep bears upon the sandy soil over whose expanses the creature is adapted to move. This padded sole is to the camel what the solid hoof is to the horse, it fits him exactly for the sort of ground over which his ancestors have stalked and shambled for countless generations. And it is interesting to note the similarities and differences which natural selection has brought about in the case of these two chief human beasts of burden.

In both the foot has become adapted for scouring the open plain only; firmness and sureness of tread have been the sole qualities that really told, and hence, in both, the toes as such have become practically extinct, and in their place one gets at last a single united broad-based foot, such as gives the animal the most secure foundation for his heavy body upon the level ground.

Compare for a moment these two types of practically toeless foot with the grasping hand of the forestine monkeys, the sharp claws of the tree-haunting squirrels, the light paw of the leaping hare, or even the slender and delicate ungulate feet of the gazelles and the chamois, and you will see how wholly they have been specialized for their work as trotters only. In the ruminants generally, as in all the great division of hoofed mammals, the extremities are calculated for support alone; but in the horse and in the camel this restriction of function reaches its highest practical point, and the feet and legs exist merely as adequate and extremely stable props for the heavy framework. In the horse the solid hoof remains as the sole surviving toe out of the original five possessed by his primitive ancestors in the American Eocene (though the "splint-bones," well known to the veterinaries, are the last functionless relics of two other toes); in the camel the same result is practically attained by the union of the two toes which it still possesses through the medium of a single horny sole, as well as by