STIFLE-JOINT LAMENESS. 295 



is generally bent, the thigli flexed upon the pelvis, and the 

 leg upon the thigh, so that the articular surfaces of the bones 

 are separated, and prevented from pressing against each 

 other; but when made to move, the relative positions of the 

 various bones are altered, and, instead of being flexed, the 

 stifle is maintained in a rigidly extended state. In this 

 manner the joint is locked, its movements suspended, and, as 

 a result, the heel of the foot touches the ground first. This is 

 more especially the case when the posterior part of the joint is 

 diseased. 



In lameness from disease of the bursa-patellae, the horse 

 generally walks with his toe dragging the ground, as if he 

 were afraid to bring the rectus femoris and vasti muscles into 

 action to elevate the patella on the trochlea of the femur ; the 

 forward movement of the limb being performed with great 

 difficulty, the toe of the foot describing the segment of a circle 

 at each step. These symptoms are, however, not constant; 

 some cases of well-marked patella lameness put the heel to the 

 ground first. But in aU instances the position while stand- 

 ing is that of semi-flexion, this being the best calculated to 

 insure separation of the various articular surfaces, and prevent 

 pressure. 



Dissection of stifle-joint lameness reveals a condition of in- 

 flammation of the synovial membranes, of the condyles of the 

 femur, and the articular head of the tibia; degeneration into 

 shreddy masses of the semi-lunar discs, laceration of their liga- 

 ments, removal of the articular cartilage, or its calcification and 

 removal by friction. 



When confined to the bursa-patellae, the alterations of struc- 

 ture consist in the removal of the articular cartilage from the 

 patella and trochlea of the femur, aind thickening of the synovial 

 membrane from interstitial inflammatory exudation. 



The bursa-pateUse is situated superficially, and when in- 

 flamed the increased secretion poured into it causes a swelling 

 in front of the joint. This swelling must not be confounded 

 with an apparent enlargement of this part, seen in the healthy 

 stifle when the animal stands with the limb in a semi-flexed 

 easy position, when "he stands resting it," as it is commonly 

 called. The swelling arising from disease is persistent, hard, 

 and prominent when the limb is extended; but the enlarge- 



