GASTROCNEMIUS MUSCLE AND TENDO-ACHILLES 139 



muscle remains more elongated than the corresponding division of 

 the muscle of the opposite limb, so that there will be permanent 

 interference with the action of the affected limb. The animal 

 should not be caused to resume work until lameness has entirely 

 disappeared. 



In very old animals, where it is suspected that the rupture is not 

 due to accident, the process of repair will, as Williams states, be very 

 doubtful and unsatisfactory. 



THE GASTROCNEMIUS MUSCLE AND THE TENDO- 

 ACHILLES 



This muscle has two heads. The outer head arises from the outer 

 lip of the supra-condyloid fossa of the femur, the inner from the supra- 

 condyloid crest. The two heads unite and are succeeded by a thick, 

 powerful tendon, which at first is placed immediately behind that of the 

 flexor perforatus. A short distance above the hock the latter tendon 

 twists round that of the gastrocnemius and becomes placed posteriorly to 

 it. The gastrocnemius tendon becomes inserted into the depression 

 which is found on the summit of the tuber calcis. 



The gastrocnemius muscle is the great extensor of the hock, and it is 

 also a flexor of the stifle. As already stated, it is the antagonist of the 

 flexor metatarsi. 



The tendon of the gastrocnemius is in a position where it is particu- 

 larly exposed to risk of traumatic injury, and cases of such injury have 

 been frequently reported. Malicious section of the tendon is not un- 

 known. Accidental rupture of the tendon is usually due to violent and 

 sudden contraction of the muscle, such as occurs in heavy draught horses 

 when shafting loads down-hill on slippery ground. The limb slips 

 forwards beneath the body, and the hock becomes suddenly and violently 

 extended. Rupture also occurs in steeplechasers when jumping. Usually 



