BOG SPAVIN 127 



outwards, in fact until it formed an angle of about 100° with the upper 

 portion of the limb. 



" Crepitation could not be detected, neither did the movement appear 

 to occasion pain. 



" Treatment being impracticable the animal was immediately 

 slaughtered. 



" A dissection of the joint disclosed rupture of a portion of the synovial 

 membrane and the entire internal lateral ligament. The distal extremity 

 of the tibia was displaced outwards but none of the bones were fractured " 

 {Veterinary Record, November 9, 1907). 



BOG SPAVIN 



A description of the arrangement of the synovial membrane of the 

 true hock joint has already been given. When this membrane becomes 

 unduly distended owing to the accumulation of an abnormal amount of 

 synovia within, the condition known as bog spavin is constituted. As 

 the synovia accumulates, the membrane forms a bulging which is visible 

 on the exterior in the position in which there is least resistance, and 

 this is found to be in the depression which is visible on the antero- 

 internal aspect of the upper half of a normal hock. The membrane is 

 here only supported by the thin, sheet-like anterior common ligament. 

 The first alteration in conformation will then be a filling of this 

 depression. Later there will appear in its stead a rounded enlargement, 

 which may attain enormous proportions. When the skin covering 

 this part becomes very tense, resistance will be offered to the further 

 distension of the membrane in this direction, with the result that a 

 bulging of the membrane appears at the back of the joint. This appears 

 in the hollow of the hock immediately behind the lateral ligaments. 

 The posterior common ligament which here supports the synovial 

 membrane, although a firmer structure than the anterior ligament, is 



