390 



HEALTH AND DISEASE 



distinguished member of the veterinary profession, first indicated the actual 

 seat and nature of the disease, which he spoke of as "coffin-joint Lameness". 

 A few years later Mr. James Turner very considerably added to our know- 

 ledge of the malady, since which time it has been known by the term 

 navicular disease, and more recently as navicularthritis. 



As to the precise nature of the disorder, it is now pretty generally 

 regarded by veterinary surgeons as an ulceration or caries of the navicular 

 bone. Commencing at first in a subacute inflammation of the ossific struc- 

 ture, the bony tissue gradually undergoes solution and removal at one or 

 several centres, as a result of which minute holes occur near to the surface 



and gradually extend themselves 

 inward and outward, until two 

 or more joining together form 

 large ulcers and excavations, dur- 

 ing which the articular cartilage 

 covering the bone undergoes a 

 process of softening and removal. 

 The bone having lost its smooth- 

 nesis, now presents a rough and 

 eroding surface to the flexor ten- 

 don on which it rests, with the 

 result that by constant rubbing 

 of the latter against the former, 

 the tendon becomes irritated and 

 inflamed, and later swollen and 

 softened, when its weakened fibres 

 gradually break away and impart 

 to its articular surface a rough and ragged condition. Associated with 

 these changes in the bone and tendon, chronic changes in the synovial 

 membrane are also observed, so that one after another all the structures 

 of the joint sooner or later become implicated in the disease. If during 

 its progress the patient is allowed a prolonged rest, the tendon frequently 

 unites with the bone, when all movement between the two ceases to exist. 

 Rupture of the tendon and fracture of the bone are ulterior consequences 

 of the disease. 



Causes. — From the great diff"erence in susceptibility to this affection 

 presented by different animals, and the evidence afforded by the family 

 history of some, heredity would seem to exercise an important predisposing 

 influence in its causation. 



That bad shoeing, by inducing weakness and contraction of the foot, 

 operates also as a predisposing factor there is no room to doubt, and 



Yig. 403. — Sections of Navicular Bone, healthy and diseased 



A, Section of healthy hone ; B, Section of diseased 

 bone permeated by carions tracts. 



