Let us turn in the first place to the fore-limb.  In most quadrupeds, as in ourselves, the fore-arm contains distinct bones called the radius and the ulna.  The corresponding region in the horse seems at first to possess but one bone.  Careful observation, however, enables us to distinguish in this bone a part which clearly answers to the upper end of the ulna.  This is closely united with the chief mass of the bone which represents the radius, and runs out into a slender shaft which may be traced for some distance downwards upon the back of the radius, and then in most cases thins out and vanishes.  It takes still more trouble to make sure of what is nevertheless the fact, that a small part of the lower end of the bone of the horse’s fore-arm, which is only distinct in a very young foal, is really the lower extremity of the ulna.

What is commonly called the knee of a horse is its wrist.  The “cannon bone” answers to the middle bone of the five metacarpal bones, which support the palm of the hand in ourselves.  The “pastern,” “coronary,” and “coffin” bones of veterinarians answer to the joints of our middle fingers, while the hoof is simply a greatly enlarged and thickened nail.  But if what lies below the horse’s “knee” thus corresponds to the middle finger in ourselves, what has become of the four other fingers or digits?  We find in the places of the second and fourth digits only two slender splint-like bones, about two-thirds as long as the cannon-bone, which gradually taper to their lower ends and bear no finger joints, or, as they are termed, phalanges.  Sometimes, small bony or gristly nodules are to be found at the bases of these two metacarpal splints, and it is probable that these represent rudiments of the first and fifth toes.  Thus, the part of the horse’s skeleton which corresponds with that of the human hand contains one overgrown middle digit, and at least two imperfect lateral digits; and these answer, respectively, to the third, the second, and the fourth fingers in man.

Corresponding modifications are found in the hind limb.  In ourselves, and in most quadrupeds, the leg contains two distinct bones, a large bone, the tibia, and a smaller and more slender bone, the fibula.  But in the horse, the fibula seems, at first, to be reduced to its upper end; a short slender bone united with the tibia, and ending in a point below, occupying its place.  Examination of the lower end of a young foal’s shin-bone, however, shows a distinct portion of osseous matter, which is the lower end of the fibula; so that the apparently single lower end of the shin-bone is really made up of the coalesced ends of the tibia and fibula, just as the apparently single lower end of the fore-arm bone is composed of the coalesced radius and ulna.

The heel of the horse is the part commonly known as the hock.  The hinder cannon-bone answers to the middle metatarsal bone of the human foot, the pastern, coronary, and coffin bones, to the middle toe bones; the hind hoof to the nail, as in the fore-foot.  And, as in the fore-foot, there are merely two splints to represent the second and the fourth toes.  Sometimes a rudiment of a fifth toe appears to be traceable.