CORACO-BRACH TALIS 305 



septa, which separate the muscle from the subscapularis, the teres minor, and infra- 

 spinatus. 



Insertion. — The inner hp of the bicipital groove from the lower border of the 

 lesser tul)erosity for about two inches (5 cm.) down the humerus. 



Structure. — Its origin is by fleshy fibres which pass upwards, outwards, and 

 somewhat forwards, to be inserted by a strong tendon, which is first visible upon 

 the outer Ijorder, and then upon the anterior surface of the muscle, and which is in 

 close relation with the l)ack of the tendon of the latissimus dorsi. A small bursa 

 intervenes b(4\veen the Iavo tendons. 



Nerve-supply. — From the posterior cord of the brachial plexus (through the 

 sixth and seventh cervical nerves) by the lower subscapular nerve, which enters the 

 muscle upon its anterior aspect close to the middle of its inner Ijorder. 



Action. — It assists the latissimus dorsi as a strong adductor, and in some posi- 

 tions of the arm as an internal rotator of the humerus. 



When the arm is fixed it will act with the latissimus dorsi in drawing the body 

 upwards, as in climbing. Its influence, however, will be exerted upon the lower 

 angle of the scapula, while that of the latissimus dorsi is chiefl}' upon the trunk 

 and ]:)elvis. 



Relations. — In front lie the latissimus dorsi, both heads of the biceps, the 

 coraco-l)rachialis. the pectoralis major, the axillary vessels, and the lower branches 

 of the brachial plexus; behind, the latissimus dorsi, teres minor, the long and outer 

 heads of the triceps; between its upper border and the subscapularis muscle are the 

 posterior circumflex and dorsalis scapulae vessels, and the circumflex nerve; below 

 are the superior profunda vessels and the musculo-spiral nerve. 



7. CORACO-BRACHIALIS 



The coraco-brachialis — named from its attachment to the coracoid process and 

 the upper arm {brachuiui) — is a cylindrical muscle, but somewhat fusiform at the 

 extremities. 



Origin. — (1) The tip of the coracoid process; (2) the inner side of the tendon 

 of the sliort head of the biceps. 



Insertion. — (1) The rough impression two or three inches long upon the inner 

 border of the humerus in its middle third, and in front of the internal interaiuscular 

 septum (see page 306); (2) the internal intermuscular septum and an aponeurotic 

 band which extends upwards from the septum in front of the tendons of the teres 

 major and the latissimus dorsi to the lesser tuberosity of the humerus. 



Structure. — It arises from the coracoid process l)y a short tendon, which is 

 blended upon its inner side with the insertion of the pectoralis minor, and from 

 the short head of the biceps by fleshy fibres for three or four inches (8-10 cm. ) 

 Ix'low the coracoid j^rocess. From this origin the fil)res run parallel to one another, 

 and are inserted by a short tendon. The muscle is frequently divided into two 

 planes between which the external cutaneous nerve passes. 



Nerve-supply. — From the outer cord of the brachial plexus (through the 

 seventh cervical nerve) by the musculo- cutaneous branch, Avhich either pierces it 

 about the middle upon its way to the biceps and brachialis anticus, or sends a 

 branch to it in this position, while the rest of the ner\-e passes in front of the 

 muscle. 



Action. — To adduct and flex the humerus. As it lies at so small an angle with 

 the axis of that l)one, it assists materially in pressing the head of the humerus 

 against the glenoid ca\'ity, and so helps to prevent dislocation. 



Relations. — Superficially, the deltoid and pectoralis major; deeply, the sub- 

 scapularis, latissimus dorsi, teres major, and triceps. Upon its outer side lies the 

 short head of the biceps; upon its inner side the pectoralis minor, the axillary and 

 brachial vessels, with the median ner\'e and other l)ranches of the brachial plexus. 



Variations. — The coraco-brachialis varies chiefly in its insertion, which may extend as high 

 as the cai)sule of the shouMer or the lesser tu}>erosity. occasionally forming in this position a 

 separate muscle (the rotator humeri); or it may descend as low as the inner condyle. It some- 

 times sends a slip to the triceps or brachialis anticus. 

 20 



