The success which has been attained in our ordinary large herbivora, and which has made them competent to evade the chase of the beasts of prey, has been accomplished by reducing the number of the toes, giving the strength of the aborted parts to increase the power of those remaining. The result is the formation of two great groups, the double-hoofed forms, including the pigs, deer, cattle, sheep, and their kindred, and the single-toed species, of which our horse is the foremost example. In the reduction of the number of toes, different plans were followed in each of these groups. In the cloven-hoofed forms, a single toe first disappeared, leaving but four; then the two outer of these were aborted, leaving two nearly equal digits. In the series of the horse, where we can trace the change more clearly, we find the earliest form five-toed, but the outer and inner digit shrunken so as to become of little use. This condition of the creature in the early Tertiaries gives us the beginning of the equine series, and shows that far away as the creature is now from ourselves, it originated from the main stem of mammalian life, from which our own forms have sprung. In the next higher stage in time, and likewise in development, we find these lessened toes at their vanishing point, and two of the remaining digits, lying on either side of what corresponds to the middle finger in our own hands, beginning to shrink in length and volume, while the central toe becomes larger and stronger than before. Last in the series we come to our ordinary equine form, in which nothing is left but the single massive extremity, though the remnants of two of the toes can be traced in the form of slender bones known as splints, which are altogether enclosed within the skin which wraps the region about the fetlock joints.
As if it were to show to us the history of this marvellous organic achievement, nature now and then, though seldom—perhaps not oftener than one in ten million instances—sends forth a horse with three hoofs to each leg. Two of these are small and lie on either side of the functioning extremity. Each of these hoofs is connected with a splint-bone which has in some way suddenly become reminded of its ancient use, and develops in a manner to imitate the creatures which passed from the earth millions of years ago. In most cases the splint-bones have no function whatever to perform. They are indeed superfluous and injurious parts, and are likely from time to time to be worse than useless, becoming the seats of disease. In this beautiful instance, perhaps the fairest of all those showing how the highly developed forms of our time retain a memory of their ancestral life, we see how the advance in the series of the horse has been effected against the resistance ancient organic habit opposes to all gains. We can therefore the better understand how the building of the hoof represents the labor of geologic ages during which the slow-made gains were won.
In its present elaborate form, the hoof of a horse is the most perfect instrument of support which has been devised in the animal kingdom to uphold a large and swiftly moving animal in its passage over the ground. The original toe-nail, and the neighboring soft parts connected with it, have been modified into a structure which in an extraordinary manner combines solidity with elasticity, so that it may strike violent blows upon the hard surface of the earth without harm. The bones of the toe to which it is affixed have enlarged with the progressive loss of their neighbors of the extremity, until they fairly continue the dimensions of the bony parts of the leg. Moreover, they have lengthened out, so as to give the limb a great extension, and this, in turn, magnifies the stride which the creature can take in running. The result is that the horse can carry a greater weight at a swifter speed than any other animal approaching it in size.
On Rotten Row, Hyde Park, London
The needs which led, in a slow accumulative way, to the invention of the admirable contrivance of the horse's foot, were doubtless founded on the necessities of swift movement in fleeing from the great predaceous animals. Incidentally, however, as this development has gone on, the peculiarities of the extremity have proved highly advantageous in defence, and the creatures have acquired certain peculiar ways of using their feet effectively to this end. The solid character of the hoof, its considerable weight, and the great power of the muscles of the hams, which are the principal agents in propelling the animal, make the hind feet capable of delivering a very powerful blow. The measure of its efficiency may be judged from the fact that a lion has been slain by a stroke from the foot of a donkey, and in their wild state a herd of horses with their heads together, can beat off the attack of the most powerful beasts of prey. In using the hind feet for assault or defence, horses have adopted an effective method of kicking which is unknown among other animals. Resting on their fore-legs, the hinder feet are thrown backward and upward, so that they may strike a blow six feet from the ground. Many of our cloven-footed animals have learned to strike cutting blows with the sharp hoofs of their fore-limbs—our bulls will stamp a fallen enemy with great force; but the backward kick of the horse is a peculiar movement, and is distinctly related to the peculiar structure of the animal's extremities.
It is an interesting fact that the development of a long and slowly elaborated series leading to the making of the horse appears to have taken place mainly, if not altogether, in the region about the headwaters of the Missouri River. In the olden days when this great work was done, that part of our continent was a well-watered country, much of its surface being occupied by great lakes which have long since disappeared. In the deposits accumulated in these bodies of fresh water are found the bones of the olden species telling the history of their series. It is not yet certain that the final step of the accomplishment which gave us our existing species was effected in this land. It seems indeed most likely that the ancestral form of our domesticated horses found their way to the continents of the Old World, and there underwent the last slight changes, before they were made captive by man. If there ever were perfect horses on this continent, they had passed away from its area before the coming of man to the land. The history of our aborigines would have been quite other than it has been, if they had had a chance to win the assistance of this noble helpmeet.