1 86 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 268. — The muscles of the posterior surface of the left scapula and the neighboring portion of the 

 extensor surface of the upper arm. 

 The deltoid has been removed with the exception of its origin and insertion; portions of the dorsal muscles inserting 

 into the vertebral border of the scapula and also of the latissimus dorsi and pectoralis major have been retained. 



Fig. 269. — The muscles of the anterior surface of the left scapula and the neighboring portion of the 

 flexor surface of the upper arm. 

 Portions of the thoracic, cervical, and dorsal muscles which insert into the scapula or humerus have been retained. 



eminence; (2) the muscles of the hypothenar eminence; and (3) the lumbricales (four) 

 and the interossei (seven). The palmar is brevis is also situated in the hand. The muscles of the 

 thenar group are the abductor pollicis brevk, the flexor pollicis brevis, the opponens pollicis, and 

 the adductor pollicis; those of the hypothenar group are the abductor digiti V brevis, the flexor 

 digiti V brevis, and the opponens digiti V. The interossei are composed of the interossei dorsales 

 (four) and the interossei volar es (three). 



THE MUSCLES OF THE SHOULDER. 



The deltoideus (Figs. 268 and 270) is a thick, triangular, markedly curved muscle which 

 is situated in the deltoid region. It arises, opposite to the insertion of the trapezius, by short 

 tendons from the acromial third of the clavicle and from the border of the acromion, by a wide 

 aponeurosis from the entire length of the spine of the scapula, and partly from the infraspinatus 

 fascia (see page 207). Its fibers, which are grouped into coarse fasciculi separated by deep inter- 

 spaces, converge toward intramuscular septa, so that the muscle rapidly diminishes in size as 

 it passes toward its insertion, which is into the deltoid tuberosity of the humerus. The 

 upper surface of the insertion is muscular; the lower is tendinous and is separated from 

 the greater tubercle of the humerus by a large bursa, the subdeltoid bursa (Fig. 268). 



The anterior border of the deltoid is practically in contact with the clavicular portion of 

 the pectoralis major, although between the two muscles there is usually a quite narrow space, 

 the deltoideo-pectoral triangle, which becomes broader as it approaches the clavicle and in which 

 runs the cephalic vein. The posterior border of the muscle is in relation with the infraspinatus, 

 the fascia of which partly covers its under surface, and the entire upper border is in contact with 

 the trapezius. Its insertion is embraced by the origin of the brachialis. 



The deltoid is supplied by the axillary (circumflex) nerve. It elevates the arm to the horizontal plane. 



The supraspinatus (Fig. 268) is a triangular, moderately strong muscle which fills the 

 supraspinatus fossa and is completely concealed by the insertion of the trapezius. It arises 

 from the entire extent of the supraspinatus fossa and from the enveloping supraspinatus fascia. 

 The markedly narrowed tendon of insertion passes beneath the acromion and the coracoacromial 

 ligament, immediately above the articular capsule of the shoulder-joint (to which it is adherent), 

 and is attached to the uppermost facet of the greater tubercle of the humerus. 



The infraspinatus (Fig. 268) is also triangular, but it is stronger and broader than the 

 supraspinatus. The outer half of the muscle is covered by the deltoid, while the inner half is 



