Page:Popular Science Monthly Volume 15.djvu/35

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25
CLEWS IN NATURAL HISTORY.

three joints or "phalanges" (1, 2, 3) composing his third finger. These joints are well known in ordinary life as the "pastern," "coronary," and "coffin bones"; and the last bears the greatly developed nail we call the "hoof."

Thus the horse walks upon a single finger or digit — the third; and it behooves us to ask what has become of the remaining five — the highest number of fingers and toes found in mammals or quadrupeds? We find that, with the exception of other two the second and fourth fingers — the horse's digits have completely disappeared. The second and fourth fingers have left mere traces, it is true, but it is exactly these rudimentary fingers which serve as the chief clews to the whole history of the equine race. On each side of the single palm-bone of the horse's great finger, we see two thin strips of bone (one of which is represented at m2 Fig. 10), which veterinary surgeons familiarly term "splint-bones." (See also Fig. 12 A, d). But these "splints" bear no finger-bones, and the condition of the horse's "hand" or fore-foot is therefore seen to be of most noteworthy and curious conformation. It may, indeed, sometimes happen that the small pieces of gristle or cartilage may be found at the base of the splint-bones, and comparative anatomists incline to regard these gristly pieces as the representatives of the first and fifth fingers. But the ordinary condition of the horse's hand may be summed up by saying that the animal walks on one well-developed finger — the third — and possesses the rudiments, in the form of the "splint-bones," of other two fingers, the second and fourth. These latter, it need hardly be added, are completely concealed beneath the skin and other tissues of the limb. In the hind-limb of the horse (Fig. 11), a similar modification is observed. The thigh-bone (f e) and knee-cap (p) are readily observed. There is but one toe — the third (l, 2, 3) — supported by a single cannon-bone (mt2); and there are likewise two splint-bones (one depicted at m2 ), representing the rudiments of the second and fourth toes. The horse's heel, like his wrist, appears out of place, and is popularly named his "hock." The shin-bone (t) is the chief bone of the leg, and has united to it the other bone (fi) succeeding the thigh, named the fibula, and which is seen in man's leg, and in that of quadrupeds at large.

To the eyes even of an unscientific observer, who sees the skeleton of a horse placed in a museum, in contrast with the bony frames of other and nearly related animals, the equine type is admittedly a very peculiar and much modified one. In place of five toes, we find but one; and in the matter of its teeth, as well as in other features of its frame, the horse may be said to present us with an animal form which appears as a literal example of Salanio's remark that

Nature hath framed strange fellows in her time.

A person of a thoroughly skeptical turn of mind might possibly demand to know the exact reasons for the assumption that the splint-