MUSCLES OF THE SHOULDER. 



the axilla. The latissimus dorsi muscle, sweeping round from the back, covers 

 its axillary surface on its way to its insertion. The muscle forms the inferior 

 boundary of a triangular space in the posterior wall of the axilla, of which the other 

 boundaries are, above, the borders of the subscapularis and teres minor . muscles, 

 and laterally the surgical neck of the humerus. This space is subdivided by the 

 long head of the triceps brachii, which passes behind the teres major muscle, into 

 (a) a quadrilateral space above, for the passage of the axillary nerve and posterior 

 circumflex artery of the humerus ; and (6) a smaller triangular space below, for 

 the circumflex scapulae artery. 



Nerve-Supply. The teres major is supplied, along with part of the subscapularis muscle, 

 by the lower subscapular nerve (C. 5. 6.), 



Action. A medial rotator of the humerus. 



M. Subscapularis. The subscapularis is a large triangular muscle which 

 covers the. costal surface of the scapula. It arises by fleshy fibres from the whole 

 of the subscapular fossa and the groove along the axillary margin, excepting the 

 surfaces at the angles of the bone (Fig. 333, p. 372). Springing from several 

 ridges in the fossa are fibrous septa projecting into the substance of the muscle, 

 which increase the extent of its attachment. 



Converging to the head of the humerus, the muscular fibres are inserted by a 

 broad, thick tendon into the smaller tubercle of the humerus and into the capsule 

 of the shoulder-joint, and by fleshy fibres into the surgical neck and the body of 

 the humerus distal to the tubercle for about an inch, under cover of the coraco- 

 brachialis and short head of the biceps (Fig. 336, p. 376). 



This muscle forms the greater part of the posterior wall of the axilla. Its 

 medial or anterior surface is in contact with the serratus anterior and the axillary 

 vessels and nerves. It is separated from the neck of the scapula by a bursa, 

 which is in direct communication with the synovial cavity of the shoulder-joint. 



The subscapularis minor is an occasional muscle situated below the capsule of the shoulder- 

 joint. It arises from the axillary border of the scapula below the subscapularis, and is inserted 

 into the capsule of the joint or the proximal part of the body of the humerus. 



Nerve-Supply. There are two and often three nerves supplying the subscapularis, viz., 

 the short subscapular (C. 5. 6.), which is often double ; and the lower subscapular (C. 5. 6.), which, 

 after supplying its lateral (lower) portion, ends in the teres major. 



Actions. The muscle aids in drawing the arm forward and medially rotating the humerus. 



The principal action of the above group of muscles is on the shoulder-joint, 

 secondary actions in relation to movements of the trunk and limbs. 



1. Movements at the Shoulder -Joint. 



They have also 



The various movements at the shoulder-joint are greatly aided by the muscles acting on the 

 shoulder girdle. In raising the arm above the head, for instance, the humerus is brought to the 

 horizontal position by the deltoid and supraspinatus, and the movement is continued by the 



