It appears, then, that, unlike the majority of mammal hands, the horse is peculiar. Instead of five bones corresponding to the palm bones, it has only one, which is called the ‘cannon bone;’ and this is followed by but one digit or finger with a huge nail. The horse then walks upon a single finger, viz. the third, on each fore foot and each hind foot. Why is this? and can we discover the history of this modification? Examine the cannon bone of a horse with care; you will find fixed on either side of it two delicate bones, called ‘splints,’ with actually no mission in the economy of the extant horse. Now go steadily back in geological time. There are three great geological epochs, the primary, the secondary, and the tertiary. The recent period called the quaternary is a sub-section of the last. Now in the quaternary and upper tertiary, fossil horses are found. They correspond with the horses we see. But in the middle of the tertiary epoch we come upon the horse, not only in Europe, but in India, and above all in America, with the splint bones, that we find in extant horses fixed to the cannon bone, as long as that bone itself, and provided with small spurious or useless hoofs, while the ulna can be traced for its whole length. In the earliest miocene deposits the horse is found with these spurious or partially aborted toes, no longer useless, but having the full length of the middle toe; making the horse of that epoch a distinctly three-toed creature, and each toe operative; while the forearm is in a condition normal to mammals. Yet another form, found in America, shows, not only the three distinct and useful toes, but upon the third toe a splint, suggesting a rudiment of the little or fifth finger; while in the oldest of the tertiary rocks has again been found a horse with the fourth finger complete. While finally, in the very earliest tertiary deposits is found a horse with a foot of four perfect digits, consisting of the second, the third, the fourth, and fifth fingers, with a rudiment or splint of the first finger distinctly visible. Similar facts reveal themselves in relation to the hind feet and legs; and slow variations palpably affected the entire body of the successive types of horse; the teeth, for example, undergoing remarkable successive modifications: and whilst the _Eohippus_ and the _Orohippus_, the last types of horse, discovered respectively in the oldest and later of the eocene beds, possess forty-four teeth, as in a large number of fossil and extant mammalian forms, the recent horse has the number reduced to forty, and their forms remarkably altered, as the final outcome of a succession of modifications.