PATHOLOGY OF SPAVIN. 81 



And not only does the hock itself suffer, until every joint consti- 

 tuting it has become carious and ossified — the articulation between 

 the tibia and astragalus being the last to contract the disease, 

 hence the reason, as I said before, of spavined horses being able, 

 lame though they be, to work on — -but parts in the immediate 

 vicinity likewise contract similar disease, among which the liga- 

 ments at the back of the hock joint, and the suspensory ligament 

 at its place of origin, are the most commonly so affected. 



Various pathological causes for the lameness in spa- 

 vin, it is evident, therefore, admit of demonstration. It was formerly 

 thought that the main or sole cause for the pain was the distention of 

 the periosteum by the tumour underneath it, the same as is said to 

 happen in the case of nodes in the human subject. I would not go 

 so far as to say a case of this description never occurs; but I 

 should certainly lay it down as my opinion that the stretching of the 

 periosteum was by no means so frequent a cause of the pain and 

 lameness in spavin as others that I will mention. The exostosis, 

 in a state of partial or entire callus, is itself in certain stages in 

 that inflamed condition that it is but natural to suppose it must 

 be the seat of considerable pain. Then there is to be taken into 

 the account — the chief source of pain, as it must be acknow- 

 ledged to be, when present — the inflammation and ulceration and 

 caries of the joints. And, further, what operates against the 

 theory of the distended periosteum is the fact of low spavin or 

 hind splent, " knots" upon the hock, as they are called, rarely 

 giving rise to lameness ; though they are calculated to put the 

 periosteum on the stretch quite to the same degree as true spavins. 

 One argument, however, there exists in favour of the distention 

 of the periosteum, and that is, the asserted fact of lameness having 

 been known to be relieved — some say cured — by division of the 

 stretched membrane, an operation called periosteotomy, whereof it 

 will become my business to speak hereafter. 



VOL. IV. M 



