SYNOVIAL SHEATHS OP THE FORE LIMB. 817 



size varies greatly ; sometimes they can only just be detected, 

 sometimes they are as large as a goose's egg. Occasionally they 

 appear below the fetlock at the back of the pastern, and are then 

 of a more flattened form. Wind galls are very common. They 

 generally result from chronic synovitis, and are often found 

 indurated in old horses. 



(C) Distension of the sheath or bursse of extensor tendons. The 

 most important are : — 



(1) Distension of the sheath of the extensor suffraginis. This 

 consists of an elongated swelling beginning at the lower end of the 

 radius, on the outside of the knee, and extending downwards ; in 

 some cases it may even encroach on the front of the joint (Fig. 473, c). 



(2) Distension of the sheaths of the extensor tendons in front 

 of the carpal joint. 



(a) The sheath of the extensor pedis, which begins above the 

 knee-joint, passes through the outer furrow in the lower end of the 

 radius, and over the front of the carpus as far as the upper end of 

 the metacarpus (Figs. 471 and 472, /). On account of its being 

 clothed in a strong fascia, dropsy of this sheath seldom occurs. 



(b) The sheath of the extensor metacarpi magnus begins at about 

 the same height ; and extends through the middle furrow in front 

 of the radius as far as the lower row of carpal bones (Figs. 471 and 

 472 g, 473 a). 



(c) The tendon of the oblique extensor of the metacarpus is pro- 

 vided with a small sheath or bursa in the groove at the lower end 

 of the radius. Distension of this bursa produces a sausage-shaped 

 swelling extending obliquely towards the inner small metacarpal 

 bone (Figs. 472 h ; 474 a). 



(d) At the front of the fetlock the tendons of the extensors pedis 

 and suffraginis are each provided with a bursa. The bursa of the 

 extensor pedis sometimes communicates with the fetlock-joint. 

 Distension may result in the formation of a very large, sometimes 

 bilobular, almost painless swelling in front of the fetlock. 



Causes. In the horse, these swellings are, with few exceptions, 

 produced by chronic irritation caused by severe continued work, 

 leading to dropsy of the joints or tendon sheaths, and are, therefore, 

 almost always confined to working-horses. 



A predisposition to them, depending on individual peculiarities 

 which are not infrequently inherited, exists in certain horses. The 

 cause is clearly some defect in the tissue, though its character is 

 not yet clearly understood. The commonest causes are of a 

 mechanical nature, such as strains, partial rupture of tendons or 



