THE POINT OF THE HOCK— CAPPED HOCK 145 



summit is the more posterior of the two convexities we described 

 when dealing with the bones. The skin is not in direct relationship 

 with the bone, since the tendon of the flexor perforatus covers this 

 portion of the summit like a kind of cap. But there are in addition 

 other structures here which are of importance, since injury to them 

 frequently results in the surgical affection well known as capped hock. 

 The posterior convexity is covered by a smooth layer of cartilage, which, 

 again, is clothed by the wall of a synovial sac or bursa. The wall of 

 this bursa also lines the deep face of the tendon, so that there is no 

 friction between the tendon and the cartilage-covered surface of the 

 tuber calcis, for the concentric faces of the wall of the bursa are what 

 come into apposition. The bursa extends upwards for a short distance 

 between the tendon of the flexor perforatus and that of the gastroc- 

 nemius. Frequently there is present another more delicate bursa, and 

 this is placed on the superficial aspect of the perforatus tendon, and 

 between it, therefore, and the skin ; its function being to prevent friction 

 between the skin and tendon during the movements of the latter. 



The prominent situation of the point of the hock renders it very 

 liable to injury as a result of blows, kicks, &c., and the term capped 

 hock is applied to any enlargement in this situation. Since the enlarge- 

 ment may be due to swelling or thickening of one or more of several 

 different structures, it will be gathered that the term capped hock is not 

 specific, but is more or less collective. Frequently the enlargement is 

 due to a swelling of the bursa which is placed immediately beneath the 

 skin, as a result of the accumulation within the bursa of a large quantity 

 of serous, blood-tinged fluid, and to this enlargement the term capped 

 hock is most commonly applied in this country. Such swellings are 

 readily seen. They are circumscribed and well defined, and they give a 

 marked prominence to the extreme point of the hock. That this bursa 

 is the one affected may be easily detected by palpation, since the tendon 

 cannot now be felt. When the swelling is due to an enlargement of the 

 bursa or sheath beneath the tendon it is much more diffused, the tendon 



