DISEASES OF THE HOCK. 309 



cussion applied to the bones themselves, or extension of inflam- 

 mation of the inter-osseous ligaments, which are, in every case 

 that I have examined, implicated in the morbid process. 



The inflammation of the bones (ostitis) originates in the 

 cancellated structure of their interior; an exudation is gradu- 

 ally thrown out between them and their cartilage, pervert- 

 ing the nutrition of the latter, whereby it ulcerates and is 

 removed, leaving the exposed surfaces of the bones in contact 

 with each other, and their cancellated structures in apposition ; 

 thus enabling their vessels to communicate with each other, as 

 already described in the chapter on Anchylosis. Concomi- 

 tant with the destructive process going on in the interior of the 

 bones, an exudate is formed upon their periosteal surface, ex- 

 tending from one diseased bone to another, binding them 

 together by a band of lymph — ultimately converted into bone — 

 which locks them firmly together, and prevents further motion. 

 In old horses the process of anchylosis is limited to the periosteal 

 surfaces, whilst the destructive action still proceeds upon the 

 articular ones ; whereas in the young or middle-aged lymph is 

 thrown out between the ulcerated surfaces of the bones, which 

 is organized into true osseous matter, making the process of 

 anchylosis complete at all points. The incurability of the 

 lameness in the old must be ascribed to this non-termination 

 of the process ; for however extensive the deposition of bony 

 matter is upon the external surface of the bones, if their exposed 

 cancelli come into contact with each other, the lameness will 

 most assuredly remain. 



We may now understand why the external deposit is not 

 the cause, but the result of the disease, and why its presence 

 is not always accompanied by lameness. So long as the 

 carious surfaces of the bones are unrepaired, so long will the 

 lameness remain; but when the bones are locked together — 

 are, in fact, converted into one bone, performing the functions of 

 one bone — the lameness disappears, and the reparative material 

 becomes as one of the essential structures of the economy. The 

 destruction of the slicrht o-lidin^ motion of these articulations is 

 of but little consequence, as it does not interfere with the flexile 

 action of the hock. 



Eeasoning upon these observations, and upon the well-known 

 fact that an old-standing spavin of the young and middle-aged 



