STRUCTURE AND DISEASES OF THE HOCK JOINT. 283 



of the joint capsule, through which the flexor perforaus tendon 

 passes on the inside of the os calcis. This cartilage, which forms, 

 as it were, a part of the capsular ligament itself, corresponds to 

 the lower posterior part of the tibia, and prevents concussion 

 between the tibia and os calcis when the leg is suddenly and 

 violently straightened as in leaping. 



The capsular ligament, just anterior to this cartilage, on both 

 sides, is the seat of thorough-pin, whilst the anterior, lower, and 

 internal part of the capsular ligament is the seat of bog spavin. 



Thus the hock joint, when the horse is at rest, may be con- 

 sidered to consist of two cavities, one in front and the other 

 behind the lower end of the tibia, for the articulating surface of 

 the astragalus is double the extent of that of the tibia. In the 

 movement of the joint, as one cavity increases the other dimi- 

 nishes ; so that when bog spavin and thorough-pin both exist in 

 the same hock, they appear alternately to increase and diminish 

 with the motion of the joint. The capsular ligament is protected 

 in front by the extensor tendons and the annular ligament. 



The perforans tendon, Ave have seen, enters a sheath at the 

 upper part of the hock on the inner side of the os calcis, and 

 continues in the sheath to the lower and posterior part of the 

 hock. This sheath is sometimes the seat of inflammation and 

 lameness. The perforatus tendon expands at the point of the 

 hock, where, being firmly bound at the sides, it forms a joint 

 capsule with the point of the hock. This capsule is not the seat 

 of capped hocks, as is frequently supposed ; for capped hock is a 

 collection of serous fluid at the back and outside the tendon, and 

 between it and the strong membranous substance underneath 

 the skin. The perforatus tendon below the cajDsule becomes 

 narrower and passes behind a strong ligament, which extends 

 from the os calcis to the metacarpal bones. A strain of this 

 ligament constitutes a curb, although the flexor tendons are 

 often involved in the mischief. — Ed.] 



Strain of the Ligaments, ^c. 



Any of the ligaments and tendons about the hock joint arc 

 liable to be strained ; and, if taken early, the horse rested, and 

 the case treated on the principles before laid down, we shall 

 generally succeed in effecting a perfect cure. When inflam- 

 mation can be detected at the hock, bleeding, from the thigh or 

 saphena vein, will effect great relief. 



By violent and long-continued exertion of the hock joint, so 

 great is the consumption of synovia, in consequence of its pecu- 

 liarly extensive motion, that the synovial membrane becomes, at 

 length, incapable of supplying any more, and in this exhausted 



