3*22 



CHAPTER XY. 



Synovial EnlargexMents. 



GENERAL REMARKS — ^^^NDGALLS OF THE FETLOCK — BOG SPAVIN — WINDGALL 

 BELOW THE HOCK — THOROUGHI'IN — WINDGALL OF THE KNEE— CAITED KNEE 

 — CArPED "WITHERS — SYNOVIAL CAPPED HOCK. 



General Remarks. 



ANATOMY. — In order to diminish friction between certain structures, 

 closed membranous sacs, containing an oily fluid called synovia (joint oil), are 

 placed between them. From injury, and sometimes, apparently from mere 

 weakness, there may ensue an eftusion of serum into one or more of these sacs. 

 Thus we have in bog spavin an enlargement of the synovial membrane which 

 lines the capsular ligament of the true hock joint ; in capped knee, we find 

 distension of the synovial bursas which facilitate the movement of the extensor 

 tendon over the front of the knee ; and in thoroughpin, there is distension of 

 the synovial sheath which allows the perforans tendon to glide smoothly over 

 the OS calcis (Figs. 98 and 130). These instances afford us examples of the 

 three actions respectively performed by the three classes of synovial mem- 

 branes, viz. : to line the capsular ligaments of joints ; to allow one surface to 

 glide over another ; and to line a canal or sheath through which a tendon 

 passes. If the effusion takes place into the joint, thereby causing distension 

 of the capsular ligament, we have "dropsy of the joint." When one of the 

 other kinds of synovial sacs becomes thus affected, the condition is termed 

 " dropsy of the bursa." 



With the exception of capped knee, which is the result of 

 injuries, these enlargements are, as a rule, signs of work in old 

 horses, and of weakness in young ones. In the great majority of 

 cases, the superabundant fluid remains unchanged, and the animal 

 suffers little or no inconvenience from its accumulation. Heat 

 and hardness are the two chief signs by which we may recognise 

 the fact that an enlargement of this kind interferes with the 

 soundness of the animal. As long as it remains cool and soft, 

 its existence will, as a rule, be of but little detriment. The 

 hardness, owing to the enlargement becoming converted into 

 fibrous tissue or bone, may remain after all heat has disappeared, 

 in which case, the presence of the deposit may interfere with the 

 action of joint, tendon, or ligament. Although synovial enlarge- 



