ENLARGEMENT OF SYNOVIAL CAVITIES IN FORE LIMB. 
557 
be considered under the head “ bursal enlargements of the extensors in 
the fetlock region,” and may be divided into upper—those of the 
extensor pedis ; and lower—those of the extensor suffraginis. 
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 coarse-bred horses and certain 
other animals. 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 
tendon sheaths, or subluxations of joints. The synovial membrane 
becomes inflamed or blood is poured into the joint cavity. In exceptional 
cases, external influences, like displacement or contusion of the joint, 
occasion enlargments of bursal cavities. Thus, bruising may be followed 
by bleeding into the capsule of the joint or tendon sheath, and years 
after the accident, flakes of fibrin may be found in the diseased joint or 
tendon sheath. 
Symptoms. The symptoms need scarcely be enumerated after what 
has gone before; and if the anatomy of the parts is borne in mind, 
diagnosis presents no difficulty. Bursal enlargements, both of the knee- 
and fetlock- joints, diminish, however, when the limb is relieved of 
weight or is flexed, whilst those of tendon sheaths become more distinct 
and appear more tensely filled. Swellings due to distension of articular 
sacs are generally horizontal, those of tendon sheaths more or less 
vertical. The presence of acute inflammation is shown by heat, 
swelling, and lameness. 
Prognosis and course. Chronic dropsy of the synovial cavities of 
joints and tendons results in the horse from chronic irritation; in 
occasional instances from acute inflammation; bursitis of the sheaths of 
the extensor tendons is generally preceded by lameness. Enlargements 
of the upper sheath of the extensor suffraginis often contain fibrinous 
clots—a result of their haemorrhagic origin—even after having been in 
existence for some time. On the other hand, enlargements developing 
either from joints or from flexor tendon sheaths are, with few exceptions, 
due to chronic irritation of the synovial membrane. Sometimes the 
cavity is filled with light-coloured, clear serum; less frequently it con¬ 
tains small bodies resembling grains of rice; occasionally the tendon 
sheath is more or less thickened (tendovaginitis chronica fibrosa) 
(indurated galls). In such case the tendon is generally involved. 
For the most part, such enlargements in horses are only regarded as 
blemishes, and in old animals are seldom entirely absent. When of 
