TH0R0UGH-1>IN. 303 



the OS calcis, the capsular ligament of the hock joint is but com- 

 paratively loosely attached, or rather, in the relaxed state, bags 

 a little ; and, being in those parts without any embrace outwardly 

 from ligament or tendon, the moment accumulation takes place 

 within the joint, the capsule at the said places bulges and pro- 

 trudes at the sides, and so produces the tumours we denominate 

 thorough-pin. This view of the pathology of thorough-pin ex- 

 plains why the swellings disappear at the time the hock is flexed, 

 and re-appear the moment the act of setting the foot down upon the 

 ground causes extension of the joint. Flexion occasions tension 

 of the capsule and pressure of the fluid {synovia) into the interior 

 of the joint ; extension, on the contrary, relaxes the capsular liga- 

 ment, while the reflux of the fluid into it occasions the bulging ; 

 the bulging taking place at the sides for the reason of there being 

 thereabouts no ligaments or tendons to oppose the protrusion. We 

 now perceive the reason, too, why thorough-pin has no existence 

 independently of bog spavin. Both anormalities consisting in 

 distention of the hock-joint with synovia, the pressure of the fluid 

 being greatest below, and the capsular ligament being least sup- 

 ported on the inner side, the bulging will take place there — in the 

 site of bog spavin — the first ; and when that part has become so 

 distended that resistance begins to be set up — from the skin, and 

 perhaps the vein, as well as the capsule itself — then does the fluid 

 (supposing accumulation still to be going on) make its way into 

 the upper compartment of the joint, and produce thorough-pin. 

 Consequently, in the normal or ordinary state of parts, thorough- 

 pin must for its presence be completely dependent upon bog spavin, 

 though bog spavin does not necessarily entail thorough-pin. 



Although we feel no apprehension about this account being per- 

 fectly intelligible to persons in the profession who are acquainted 

 with the structure of the hock-joint, yet we are apprehensive it 

 may turn out in some respects not to be altogether so to persons 

 out of the profession ; to whom all that we can, by way of solution, 

 recommend is, a view of the parts themselves, either in skeleton 

 or preparation. The fluctuation felt in either tumour while the 

 one opposite is being tapped with the fingers is now likewise per- 

 fectly comprehensible. There is evident communication between 



