SPRAIN OF EADIAL LIGAMENT, 263 



ence of the nervous system, and hence beyond the possibility 

 of fatigue, the mere implanting of the feet upon the ground, 

 by causing the muscles to be stretched, produces a state of 

 rigidity and firmness in the limbs that enables the animal to 

 stand and sleep for liours together without danger of falling. 

 The muscles are strengthened and assisted by the ligament- 

 ous bands : from this circumstance, and from their acting as 

 checks to over-extension, they are liable to sprain or even 

 rupture. 



Sprain of the radial ligament is manifested by lameness, a 

 difficulty in the act of flexing the knee, with swelling, heat, 

 and tenderness immediately above the knee, posterior to the 

 radius. The swelling arises from exudation of lymph into the 

 substance of and around the ligament, and from distension of 

 the synovial bursa, through which the tendons pass, behind the 

 knee. In some cases, both perforatus and perforans also are 

 involved in the injury : in such the lameness, pain, and 

 swelling are excessive, and flexion exceedingly difficult, arising 

 from the swollen tendons being too thick to play through 

 their thecas, — just as a rope too thick for a pulley retards 

 motion. 



The distension of this bursa appears as a tense but fluctua- 

 ting swelling at the back, and slightly above the knee, and is 

 sometimes called thorough-pin of the knee. 



The tendons of the various muscles concerned in the flexion 

 and extension of the knee, pastern, and foot, passing through 

 thecae upon the surfaces of the carpus, are liable to injury, 

 with distension of their various synovial sheaths from hyper- 

 secretion of synovia. We have thus the tlieca of the flexor 

 metacarpi externus made visible on the outer surface of the os 

 trapezium ; the sheath of the flexor metacarpi internus on the 

 inner side of the knee ; that of the extensor metacarpi magnus 

 in front of the knee as a swelling on either side of the tendon ; 

 and those of the other extensors upon the outer surface of the 

 carpal articulations. 



These enlargements, when arising from injury, and conse- 

 quent thickening of the tendons themselves, or inflammation of 

 the synovial membrane, cause lameness ; whilst at other times 

 they are mere bursal distensions giving rise to no inconveni- 

 ence. 



