302 THOKOUGH-PIN. 



unattended by thorough-pin. The pathology of thorough-pin will 

 explain this seeming paradox. 



The Causes of Thorough-pin, so far as they are imme- 

 diately exciting, may be said to be the same as produce bog 

 spavin. A hock that is over-weighted or over-worked, over- 

 stretched or strained in any way beyond its powers, will be likely 

 to put out a bog spavin, and afterwards may shew thorough- pin. 

 And, as was observed on another occasion, this may be expected 

 to happen to young horses in particular at the time of breaking, 

 and especially to such as have great frames with large bony 

 joints. 



In respect to Predisposition, straight hocks are more liable 

 to bog spavin and to thorough-pin than those of an opposite forma- 

 tion. On this account, young horses with such predispositions 

 should have attention paid to the shoeing of the hind feet. Since 

 caulkings may be likely, by raising the heels and so still further 

 straightening the hocks, to add to this susceptibility, it will gene- 

 rally be found advisable to have such horses' hind shoes made 

 plain in the heels. Solleysel, who treats of these affections under 

 the general heading of " windgalls," says, that *' this disease 

 (seated between the great sinew of the hock and the thigh bone) 

 is often hereditary, and derived from the stallion." And, so far as 

 conformation of hock goes towards predisposition to the disorder, 

 we quite agree with Solleysel. 



The Pathology of Thorough-pin is analogous to that of 

 bog-spavin. It consists in anormal accumulation of synovia in 

 the joint of the hock, and consequent dilatation and bulging of the 

 capsular ligament. The cavity of the hock joint may be said to 

 be naturally divided into two compartments by the trochleated 

 adaptation of the tibia to the astragalus. So long as the joint is 

 at rest and the animal is bearing his weight upon it, all communi- 

 cation between these two compartments of the joint is shut off; 

 while, on the other hand, the joint is in motion, and especially so 

 long as the hock is flexed, and all bearing is taken off it, it is pos- 

 sible for fluid to pass from one compartment into the other. More- 

 over, at the places where thorough-pin makes its appearance, viz., 

 between the lateral processes of the lower head of the tibia and 



