DISEASES OF CARTILAGE AND SYNOVIAL MEMBRANE. 313 



ihe diseases of the foot), ulceration of cartilage is not very com- 

 mon in the horse. 



Acute inflammation of the synovial membrane is seldom 

 met with ; but a chronic state, inducing an excessive secretion of 

 eynovia, is extremely common. The most usual situation is at the 

 hock, where the swelling has received the name of bag-spavin and 

 thoroughpin ; but they also occur at the fetlock and knee joints ; 

 in the former case being sometimes confounded with windgalls, 

 which are inflamed bursas mucosae. 



Bog-spavin is very apt to attack young horses, when they are 

 over-worked, before being fully seasoned ; but it may occur at all 

 ages. It shows itself at the inner side of the joint, because here 

 the ligaments are wider apart, and there is more room for disten- 

 sion. Its seat is the capsule between the tibia and astragalus, 

 which is here unprotected by any strong fibrous covering, and 

 readily yields to the gradual pressure of the secretion from its in- 

 ternal surface. 



Thoroughpin may be either an increased secretion of the syno- 

 vial capsule, between the astragalus and os calcis, or between the 

 scaphoid and cuneiform bones, or of the bursa mucosa lying be- 

 tween the tendo Achillis and the tendo perforatus. In the first 

 of these cases, it often coexists with bog-spavin, and the synovia 

 may be made to fluctuate from one bag to the other, the only line 

 of demarcation being the astragalo-calcanean ligament. 



Both hog-spavin and thoroughpin may exist, or either separately, 

 without occasioning lameness; but where they are just established, 

 there is generally some small degree of active inflammation, which 

 causes a slight lameness on first going out of the stable, but soon 

 disappearing. 



The treatment should be by pressure, kept up for a long time, 

 by means of a carefully-adjusted truss, alternated with cold afi"u- 

 sion, and the use afterwards of tincture of arnica, diluted with 

 water, as a wash. Subcutaneous scarification has succeeded in 

 some few cases in causing the secretion to cease ; but it has so 

 often produced extensive inflammation of the joint, that the opera- 

 tion is by no means to be recommended. Blistering with biniodide 

 of mercury has also occasionally answered ', but no plan is so suc- 

 cessful, on the whole, as pressure, alternating with cold afi"usion. 



Delicate young foals are subject to a rheumatic inflamma- 

 tion of their synovial membranes, specially displayed in the knees 

 and hocks, and apparently caused by exposure to cold. It seldom 

 goes on to produce disorganization of the cartilages, but the capsu- 

 lar ligaments are distended w^ith thin yellow synovia, causing 

 considerable stifi"ness. The cellular tissue around the joinrs also 

 becomes (edematous, and the legs fill all the way down to the feet. 

 It is commonly known among breeders as the ''joint evil,'' and 

 27 



