1 36 EX AM IN A TION OF HORSES 



of oil, in which case the parts must necessarily be tense 

 from over-distension. 



• Lastly, if there is disease of the joint you will have 

 lameness, heat, and over-distension ; but as a matter 

 of course your test lies in setting the machine in motion 

 and seeing what effects are produced, which will be most 

 visible, not hnmediately after the motion, but when the 

 horse has stood awhile and cooled. 



Thorough-pin is precisely of the same nature as bog- 

 spavin ; only instead of a joint, it is a tendon surrounded 

 by a lubricating sheath, that has to act like a pulley, 

 and requires well lubricating. This sheath gets over- 

 distended with oil (synovia). The perforating flexor of 

 the foot has its origin quite externally at the back of 

 the tibia, and becomes tendinous above the hock and 

 passes over the inside of the hock, and again gains the 

 middle line after it has got well below the hock, so that 

 it has quite a spiral course, which makes it lie close to 

 the internal surface of the os calcis, which is rendered 

 concave to receive it and over which it glides. In 

 passing thus obliquely from without inwards, it has to 

 pass between the point of the os calcis and the back of 

 the tibia, and the straighter the hock the nearer does 

 the point of the os calcis approach the back of the tibia, 

 therefore the more does this synovial sheath get pressed 

 upon in straight hocks. This explains its more frequent 

 appearance on good upright hocks, whose ossa calces 

 are usually shorter on account of less leverage being 

 required, and whose ossa calces are necessarily closer to 



