296 BOG SPAVIN. 



synovia, producing what we call "bog spavin." Young horses with 

 large joints put to do work or carry weight beyond their strength; 

 heavy-worked harness horses, hunters, steeple-chace horses, racers, 

 and so forth, are on these accounts the especial subjects of bog 

 spavin. And those equestrian movements that throw most stress 

 upon the hocks, such as pulling horses upon their haunches, back- 

 ing them, suddenly or violently checking or pulling them up, heavy 

 draft, &c., will operate in a peculiar manner in the production of 

 the disease. 



Between the Pathology of Bog Spavin and Windgall 

 there is this important difference — that, while windgall has a bursa 

 for its seat, bog spavin consists in enlargement and saccular dila- 

 tation of the capsule of the joint itself, viz. the joint of the hock. 

 It will be remembered that the hock is composed of several joints or 

 articulations; but that the principal of these is the one between the 

 tibia and astragalus, which, in consequence of its being that through 

 which the motion requisite for progression is mainly carried on, 

 commonly goes by the appellation of the hock joint ; and this joint 

 it is which is the seat of bog spavin. Inordinate stress or motion 

 of this joint, as has been already observed, has a tendency to pro- 

 duce irritation of its delicate lining membrane ; and this, once set 

 up, is productive of augmented synovial secretion in it : the effect 

 of which is, first, distention, and subsequently dilatation, of the 

 capsule of the joint. In place of from three drachms to half an 

 ounce of synovia, which is the quantity usually found in the joint, 

 in this anormal condition of it from two to three ounces, and even 

 more, will frequently be found to be collected : in fact, the joint 

 may truly be declared to be in a dropsical state. Under such in- 

 creased pressure the capsule of the joint gives way ; and those 

 parts of it which are weakest from want of support externally give 

 way the soonest, or in other words bulge, and form tumours visible 

 through the skin. The part of the capsule the most likely to bulge, 

 not only from its being a part unbraced by ligament or tendon, 

 but likewise from its being a dependent part, and one against which 

 the accumulated fluid is thrust by the mere weight of the animal, 

 is the inner and anterior part of the hock joint ; the site, in fact, of 

 bog spavin. 



The saccular dilatation of bog spavin once produced, there is no 



