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. [Illustration: On Rotten Row, Hyde Park, London]