BURSAL ENLARGEMENTS. 321 



There are two kinds of Thorough-pin, namely those arising from irrita- 

 tion in the true hock joint, and those which are caused by irritation or 

 sprains of the flexor pedis tendon. 



642. Thorough-pins arising from irritation of the true Hock joint. 



Thorough-pin arising from irritation of the true hock joint is in fact 

 only a further development of bog spavin. The increased secretion of 

 synovia, for reasons already given, shows itself primarily in distension of 

 the lower part of the bursa. When this portion is full, any further 

 increase shows itself in the upper part. The swelling appears equally on 

 both sides, and the fluid may by moderate pressure be forced from one 

 side to the other. Hence is derived the name of Thorough-pin, or run- 

 ning " through " from side to side. 



643. Thorough-pins arising from irritation of the Flexor pedis tendon. 



The other and more common description of Thorough-pin is not con- 

 nected with the true hock joint, but arises from irritation of the Flexor 

 pedis tendon. 



This tendon is tightly bound down at its upper part by the ligaments 

 at the back of the tibia, and again below as soon as it reaches the inside 

 of the hock. Hence, any increased secretion of synovia can only lodge 

 in the intervening space, i. e. in the hollow of the hock, either on one or 

 both sides. 



If the seat of the injury be high up (and it generally does occur, as we 

 might expect, near the bend) we find the enlargement on both sides ; but 

 that on the outside is generally larger than that on the inside. If on the 

 other hand the seat of the injury is lower down, the swelling may, on 

 account of the position of the part of the tendon injured, appear only on 

 the inside ; but it more often appears on both sides, or on the outer side 

 only. 



Thorough-pins, arising from irritation of the flexor pedis tendon, are 

 at once distinguished from those described in the preceding paragraph, 

 because there is no lower enlargement or bog spavin. It is however very 

 possible that both kinds of Thorough-pin and bog spavin also may be 

 present in the same hock. 



Bog spavins and Thorough-pins vary very much in size according to 

 the nature and degree of the particular case. They may be so small as 

 to be scarcely perceptible, or they may be of enormous size. 



644. Windgalls. 



Windgalls are similar enlargements arising from very similar causes in 

 the neighbourhood of the fetlock joints. They seldom however become 

 of any great size. They more commonly arise from over-exertion, con- 

 cussion and irritation of the parts than from actual sprain. Indeed the 

 fetlock joint is so constructed, that it is very rarely sprained. 



Similar enlargements, if any sufficient cause exists, sometimes appear 



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