DISEASES OF THE HOCK. 



311 



disease of the tendon. The fluid which fills it may, by pressure, 

 be forced from one side to the other ; hence the term thorough- 

 pin, or running through from side to side. This may be 

 described as true thorough-pin, in contradistinction to that 

 associated with very large bog-spavins. 



A thorough-pin, however large, does not cause bog-spavin, as 

 there is no real channel of communication between the true hock- 

 joint and the bursa of the perforans tendon ; but the capsule of 

 the joint swells upwards and backwards, bulges into the bursa 

 of the tendon, and a large bog-spavin may thus cause the dis- 

 tension of the bursa, and the appearance of thorough-pin. 



Tlwrougli-pins are generally found in short, fleshy, upright 

 hocks, where the os calcis is short and ill developed. We can 

 account for such hocks being subject to them by the knowledge 

 that the lever of the limb being a short one, more strain is 

 thrown upon the flexor tendons, the flexors of the foot being 

 extensors of the hock. 



• Eailway shunt horses are very liable to fall unsound from 

 thorough-pin, in consequence of the very heavy truck loads they 

 have to start. 



In the treatment of thorough-pins and bog-spavins, rest, the 

 high-heeled shoe, and pressure by a spring truss, are the most 

 effective appliances. Some recommend puncturing the sac. This 



Fig. 54. — Spring truss for thorough-pin and bog-spavin, designed 

 by Mr. Broad, Bath. 



I have performed in some cases with satisfactory results ; but as 

 a rule I think the operation should be avoided. The method of 

 puncturing the bursa subcutaneousl}^, by making a very small 

 incision and drawing out the fluid with a syphon is useless, the 

 sac becoming quite full again in the course of a few hours. If a 

 puncture is to be made at all, it should be at the bottom of the 



