Having explained the peculiarity attending some bony tumors on the hind extremity, it now becomes our duty to explain what actually constitutes a spavin. Any bony growth or bony enlargement, however small, which is to be seen or felt upon the inner side of the hock, is a "spavin." But of spavins there are three kinds. The low sort, or the "Jack" of the horse-dealer's phraseology. This answers to the splint of the fore leg, and originates in the top of the splint bone. [Illustration: A SHIN-BONE HAVING AN OSSEOUS DEPOSIT UPON ITS HEAD AND ON THE INNER SIDE, WHICH MIGHT BE A SPLINT OR A SPAVIN, AS IT OCCURRED UPON THE FORE OR HIND LEG. ] [Illustration: THE INNER SIDE OF THE HOCK AFFLICTED WITH HIGH OR INCURABLE SPAVIN. ] The bony enlargement, should it be located comparatively high upon the joint, often produces acute and incurable lameness. When low down, the granules of bone have little to interfere with. Being placed higher up, the tendons have to play over the osseous deposit; and, when that happens, the cure is hopeless. The above form of disease, however, does not ensue upon every case of spavin. Many good racers, and most seasoned hunters, have spavins, which do not in any way detract from their speed, however much these growths may interfere with their action. [Illustration: THE NATURAL POSITION OF THE HEALTHY FOOT WHEN RAISED FROM THE EARTH DURING AN EASY TROT. ] [Illustration: THE FOOT, INCAPABLE OF BEING FREELY RAISED FROM THE GROUND, BY A HORSE WHICH IS BADLY SPAVINED. ] Bony spavin does, when the quadruped starts, sensibly deteriorate that grace of motion which should characterize the action of the perfect horse. During the trot, the leg should be lifted clear of the earth, while, by an involuntary movement within the hock-joint, the hoof is inclined outward. This peculiarity is exhibited in the engraving on page 289, which supposes the spectator to be standing by the side of the animals. Exostosis, formed on any part, locks together the bones which the deposit may involve, or it unites the several distinct parts into one osseous mass. By the bones of the hock being thus joined, all movement of the shin is effectually prevented; the foot of a spavined horse is, to a spectator who is laterally situated, always presented in a side view. Moreover, when severe spavin is present, the entire flexion of the lower portion of the limb is rendered impossible. [Illustration: THE FOOT OF A SPAVINED LIMB, SHOWING THE WEAR OF THE TOE OF THE HOOF AND SHOE; BOTH ARE CONSEQUENT UPON DRAGGING THE MEMBER UPON THE GROUND. ]