12 THE SURGICAL ANATOMY OF THE HORSE 



tendons of insertion of the supraspinatus muscle. The biceps is 

 inserted into the bicipital tuberosity of the radius. 



The upper part of the biceps is visible owing to the fact that 

 the mastoido-humeralis has been almost completely removed. Two 

 or three inches of the last-named muscle are, however, represented 

 near its insertion into the external lip of the musculo-spiral 

 groove (i8). 



Behind this piece of the mastoido-humeralis is noticed part of the 

 Brachialis Anticus Muscle (17), which arises at the back of the upper 

 extremity of the humerus. It then winds round the outer side of the 

 bone in the musculo-spiral groove, where it is represented in the plate 

 (17). Its tendon of insertion, which is not visible, passes inwards 

 beneath the internal lateral ligament of the elbow to be inserted into 

 the radius and ulna. 



The Triceps Extensor Cubki. — Two divisions of this muscle are repre- 

 sented here, namely, the large and middle heads (7 and 15). 



The Caput Magnum (7) arises from the dorsal angle and glenoid edge 

 of the scapula, and is inserted into the summit of the olecranon process 

 of the ulna. This muscle fills up the greater part of the triangle of 

 which the scapula (inferior border) and humerus form two of the sides. 

 It is a powerful extensor of the elbow and a flexor of the shoulder. 



The Caput Medium (15). — This division arises from the curved 

 roughened line which runs upwards on the back of the humerus from 

 the deltoid tubercle to the articular head. The upper part of the origin 

 of the muscle is concealed by the deltoid. It is inserted with the large 

 head, and is an extensor of the elbow. 



Both these divisions of the triceps extensor cubiti are supplied by the 

 musculo-spiral nerve. 



In the region of the forearm quite a number of muscles are repre- 

 sented. 



The Extensor Metacarpi Magnus (20). — This is the most anterior of 

 the muscles here shown. Its belly, together with that of the extensor 



