SUPERFICIAL DISSECTIONS 15 



the fascia of the leg. Only about three inches of the insertion of the 

 first-mentioned part are represented, the rest of the muscle having been 

 removed to display the parts beneath it. 



The Gastrocnemius (10). — This muscle has two heads : the outer is 

 represented in the Plate, and it arises from the outer lip of the supra- 

 condyloid fossa. The two heads unite, forming the prominent bulging 

 mass which corresponds to the calf in the human leg. This mass is 

 succeeded by a powerful tendon, which descends in a vertical direction 

 to the summit of the tuber calcis, where it obtains insertion in the 

 depression separating the two elevations on this bone. The gastroc- 

 nemius is a powerful extensor of the hock joint, and is also a slight 

 flexor of the stifle. It is supplied by the internal popliteal nerve. 



The Flexor Perforatus (22 and 26). — Deeply seated to the gastroc- 

 nemius is the flexor perforatus, which is therefore concealed from view. 

 It arises from the depth of the supracondyloid fossa, and runs down the 

 limb in front of the gastrocnemius. At the summit of the calcis its 

 tendon is superposed to that of the latter muscle and forms a cap. It 

 gives off a slip of insertion to the tuber calcis on either side and takes 

 a course straight down the back of the calcis, where it is concealed by 

 the thick layer of fascia represented in the Plate. 



Below the hock the tendon is plainly visible, and its edge has been 

 displaced slightly backwards to display more effectively the structures 

 which lie in front of it. At the fetlock it forms the tube through 

 which the tendon of the flexor perforans passes, and it ultimately obtains 

 insertion into the os coronx. This muscle is an extensor of the hock, 

 and a flexor of the fetlock and pastern joints. It is supplied by the 

 internal popliteal nerve. 



The Flexor Perforans (16). — On this aspect of the limb a con- 

 siderable portion of this muscle is visible. It is placed between the 

 peroneus muscle in front and the gastrocnemius behind, occupying most 

 of the space between these two muscles from the stifle to the hock. It 

 arises from the external tuberosity and posterior surface of the shaft of 



