THE MUSCLES OF THE ARM 



259 



Structure. — It is fleshy and usually about the breadth of a finger. It may, 

 however, consist of only a few bundles of fibers; sometimes it is double. Its 

 attachment to the joint capsule is slight. It passes through the brachialis muscle 

 to reach its insertion. 



Relations. — Superficially, the teres minor and triceps muscles; deeply, the 

 teres major and subscapularis muscles, and the capsule of the joint. 



Blood-sup ply. — Posterior circumflex artery. 



Nerve-supply. — Axillary nerve. 



III. THE MUSCLES OF THE ARM 

 This group consists of five muscles which are grouped around the humerus. 

 They arise from the scapula and the humerus, and are inserted into the forearm. 

 They act on the elbow joint and the fascia of the forearm. 



Spine of scapula'--- 



External tuberosity of humerus - 



Deltoid tuberosity - 

 Biceps brachii ' 



Infraspinous fossa 



- - " Brachialis 



, - Musculo-spiral groove 



" Olecranon 



_, ^ . ,. ; «/ External lateral ligament of elbow joint 



Shaft of radius . ^ __ I 



■ - - Shaft of ulna 

 Fig. 188. — Biceps .■vnd Br.\chialis Muscles of Horse. (.\fter Ellenberger-Baum, .\nat. fiir Kunstler.) 



1. Biceps brachii (Coraco-radialis; flexor brachii). — This is a strong, some- 

 what rounded muscle, which lies on the anterior surface of the humerus. 



Origin. — The tuberosity of the scapula. 



Insertion. — (1) The bicipital tuberosity of the radius; (2) the internal lat- 

 eral ligament of the elbow joint; (3) the fascia of the forearm and the tendon of the 

 extensor carpi radialis. 



Action.— To flex the elbow joint, to fix the shoulder, elbow, and carpus in 

 standing, and to tense the fascia of the forearm. 



Structure.— The muscle is inclosed in a double sheath of fascia, which is 

 attached to the lips of the bicipital groove and the deltoid ridge of the humerus. 

 The tendon of origin is moulded on the bicipital groove; it is very strong and dense 

 and is partly cartilaginous. Its play over the groove is facilitated by the large 

 bicipital bursa (Bursa intertubercularis). The synovial membrane covers not 

 only the deep face of the tendon, but extends somewhat over the edges to the 

 superficial face. A well-marked tendinous intersection runs through the belly 

 of the muscle and divides distally into tw^o portions. Of these, the short, thick 

 one is inserted into the bicipital tuberosity and detaches fibers to the internal 



