364 



THE MUSCULATURE 



The deltoid (fig. 355) is a large, shield-shaped muscle which covers the shoulder. 

 It arises from the spine of the scapula, the acromion, and lateral third of the 

 clavicle and is inserted into the deltoid tubercle of the humerus. It abducts the 

 arm. 



The teres minor, infra- and supraspinatus form a group of muscles (fig. 363) 

 which arise from the back of the scapula, pass over the capsule of the shoulder- 

 joint, to which their tendons are adherent, and, under cover of the deltoid, are 

 inserted into the top and the dorsal margin of the great tubercle of the humerus. 

 The band-like teres minor arises from the upper two-thirds of the axillary border 

 of the scapula, and has the lowest insertion on the tubercle. The triangular 

 infraspinatus (fig. 363) arises from the whole infraspinous fossa except the axillary 

 border, and is inserted above the teres minor. The pyramidal supraspinatus 

 (fig. 363) arises under cover of the trapezius from the supraspinous fossa, and 

 has the highest insertion on the tubercle. The teres minor, supraspinatus and 

 infraspinatus act as lateral rotators of the arm, the supraspinatus also as an 

 abductor. 



The latissimus dorsi, the teres major, and the subscapularis form a group of 

 muscles attached to the lesser tubercle of the humerus and to the crest which 



Fig. 356. — Front View of the Scapular Muscles. 



Clavicle 



Coracoid process 



Supraspinatus 



Subscapularis 



Teres major 

 Latissimus dorsi 



Deltoid 



Coraco- brachialis and 

 short head of biceps 



Pectoralis major 



extends distally from this on the medial side of the intertubercular (bicipital) 

 groove. The latissimus dorsi (figs. 355, 356) is a large, flat, triangular muscle, 

 which arises from an aponeurosis covering the lumbar and the lower half of the 

 thoracic regions of the back and from the posterior part of the iliac crest, and is 

 inserted into the intertubercular (bicipital) groove. The teres major (figs. 

 355, 356) is a thick, ribbon-shaped muscle which arises from the dorsal surface of 

 the inferior angle of the scapula and is inserted behind the latissimus dorsi into 

 the distal two-thirds of the crest of the small tubercle of the humerus. The 

 subscapularis (fig. 355) is a thick, triangular muscle which extends from the 

 subscapular fossa to the small tubercle of the humerus. These muscles adduct 

 the arm and rotate it medialward. The latissmus dorsi is also the chief extensor 

 of the arm. 



Near their humeral attachments these two groups of muscles are separated 

 below by the long head of the triceps. The supraspinatus is separated from the 

 subscapularis by the l)ase of the coracoid process and by the intertubercular 

 (bicipital) groove. The tendons of the latissimus dorsi, teres major, and sub- 

 scapularis are crossed ventrally by the main vessels and nerves of the arm and by 

 the short head of the biceps and the coraco-brachialis. 



The supra- and infraspinatus muscles are supplied by the suprascapular nerve. 

 The deltoid and the; teres minor are supplied by the axillary (circumflex). The 

 sub.scapularis, the teres major, and the latissimus dorsi are supplied by subscapular 

 nerves. That to the latissimus dorsi is called the dorsal thoracic nerve. 



