282 DISEASES OF THE HORSE. 



used, a piece of leather corresponding to the shoe may be riveted 

 to both heels, which plan will considerably obviate concussion. 

 By these measures in the country we can generally relieve the 

 horse sufficiently to make him useful ; but in London it is often 

 necessary to destroy the sensation of the foot by the operation 

 of neurotomy, the merits and demerits of which will be sepa- 

 rately discussed." — Spooner on the Foot, §-c.] 



CHAP. L. 



STRUCTURE AND DISEASES OF THE HOCK JOINT. 



This is a most important joint, and one that is more exercised 

 than any other joint in the body : that is, the surface of motion 

 between its two large bones is much greater than between any 

 other bones of the body. Diseases of the hock joint have liad 

 distinct names applied to them, by which they are familiarly 

 known, and therefore I will explain them under these terms, 

 which are. Bone Spavin, Bog Spavin, Thorough-pin, and Curb. 

 But previous to an explanation of its diseases, a concise de- 

 scription of the joint may be useful. The hock is composed of 

 six bones, the principal of which are, the os calcis and the astra- 

 galus. The other four bones are considerably smaller, and have 

 been distinguished by names, which need not here be mentioned, 

 and are placed in two rows between the astragalus and the 

 cannon. The astragalus is a very curious bone, and is placed 

 obliquely in the shape of a pulley. It is articulated with the 

 leg bone or tibia, with the small bones below, and rather poste- 

 riorly with the OS calcis ; and such is the nature of these arti- 

 culations, that a most extensive motion is afforded to the shank. 

 [The motion of the hock is entirely confined to the upper arti- 

 culation, — namely, that between the astragalus and the tibia: 

 the former bone presents two round condyles, as they are termed, 

 with a deep concavity between them and the lower part of the 

 tibia is the counterpart of this, having two concavities and an 

 eminence in the middle. These bones, thus adapted, move on 

 each other in the manner of a hinge, having no lateral motion 

 but a very extensive one in a forward direction. The hock 

 joint is the most extensive articulation in the whole body, and it 

 is protected by a capsular ligament of corresponding extent. 

 This ligament is fastened to the lower end of the tibia above, 

 and to the upper row of small bones below, and to the astragalus 

 on each side behind the condyles. At the upper and back part 

 of this articulation there is a movable cartilage, whose front 

 surface forms part of the hock joint, and hind surface the front 



