Page:Popular Science Monthly Volume 15.djvu/38

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28
THE POPULAR SCIENCE MONTHLY.

horse than the latter. Our own Anchitherium (D D1) corresponds to the next specimen of the New World — Miohippus by name; and Miohippus evinces a still more important modification in that it possesses a rudiment of the fifth or little finger in addition to the second, third, and fourth digits with which the fore-feet are provided.

The American horses now continue the history of the race in time past without aid or representative from the eastern hemisphere, in so far, at least, as the latest research has shown. To Miohippus succeeds the Mesohippus (E E1) from the American Miocene, which has three well-developed toes, and in addition shows the rudiment of the little finger (E e) of the fore-feet (seen also in Miohippus, D e) in an enlarged condition. Passing to the Eocene formations, the oldest series of the Tertiary rocks, we meet with the next step in the form of the Orohippus (F F1), in which the little finger (e) appears as a veritable member of the hand, the hind-feet still possessing three well-developed toes only: while, consistently with the development of the toes, the ulna of the forearm and fibula of the leg appear as bones of legitimate size, and present a striking contrast to their rudiments in the horse of to-day. The last discovered horse is from the oldest of the Eocene beds; it has been appropriately named Eohippus, and presents us with four complete toes (second, third, fourth, and fifth) on the fore-feet, and a rudiment of the first toe as well; with a trace of the fifth toe of the hind-feet — this last member being, as we have seen, unrepresented in any of the other forms. When the Chalk. Rocks shall have yielded up their fossil horses, it is consistent with logic and reason to expect that the primitive stock of the horses will be discovered with its complete provision of five toes, and its corresponding modifications of form.

To what conclusions, of reasonable kind, do these stable facts regarding the pedigree of the horse naturally lead? The answer is toward a belief in the slow and progressive modification and evolution of the one-toed modern horse from a five-toed ancestor. This process of modification must, of course, have affected its entire frame, but it is sufficient for our present purpose to point out that in the structure of the foot alone we discern the evidence for evolution, as clearly as in the entire organization of the animal. An increase of speed, and obvious advantage over its enemies, would be gained by the horse, as its toes grew "small by degrees and beautifully less"; and the single-toed race has thus practically come to the front in the world of to-day, as the plain and favorable result of the work of degradation among its digits.

Two bony shreds or rudiments thus lay the foundation of a grave conclusion regarding the horse and its manner of development, and exemplify the adage that great and unlooked-for results sometimes spring from beginnings of apparently the most trifling kind. The "splint-bones" form, in fact, a clew which, when rightly pursued, leads not merely to a knowledge of the evolution of the horse, but to an understanding of the entire scheme of nature. The idea, then, of