192 VETERINARY MEDICINE AND SURGERY. 



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

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

 or sprains of the flexor pedis tendon. 



Thorough-pin arising from iritation 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 distention 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 thorough-pin or running 

 '' through " from side to side. 



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

 nected with the true hock joint; but arises from irritation of the per- 

 forans muscle of the tendon flexor pedis. 



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 joossible that both kinds of thorough-pin and bog spavin 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. 



Treatment. — The most active method is to puncture the sac at the 

 lowest part and allow the fluid to run off; keep the puncture open several 

 days and inject it with a mild solution of sulphate of zin^: 



