THE SHOULDER MUSCLES. 575 



base, which is formed by the axillary fascia, downward. Its ventral wall is formed 

 by the pectoralis major and pectoralis minor, its dorsal wall by the latissimus dorsi, 

 teres major, and subscapularis, and its medial wall by the serratus magnus. In the 

 angle formed by the junction laterally of its ventral and dorsal walls lies the m. coraco- 

 brachialis, and in the groove between that muscle and the posterior wall are the 

 axillary vessels and the cords of the brachial plexus. The cavity of the axilla con- 

 tains a considerable amount of fat and a variable number of lymphatic nodes ; it is 

 traversed by the thoracic branches of the axillary vessels and by the intercosto- 

 humeral nerve, and the long thoracic nerve passes downward along its medial wall to 

 the serratus magnus. 



THE MUSCLES PASSING FROM THE PECTORAL GIRDLE TO 



THE BRACHIUM. 



Prh-Axial. Post-Axial. 



I. Coraco-brachialis. i. Supraspinatus. 4. Teres major. 



2. Infraspinatus. 5. Subscapularis. 



3. Teres minor. 6. Deltoideus. 



(a) THE PRE-AXIAL MUSCLES. 



I. Coraco-Brachialis (Figs. 560, 570). 



Attachments. — The coraco-brachialis arises from the tip of the coracoid pro- 

 cess of the scapula by a tendon common to it and the short head of the biceps. It 

 extends downward along the humerus and is inserted at about the middle of its 

 medial border. 



Nerve-Supply. — By the musculo-cutaneous nerve from the seventh cervical 

 nerve. 



Action. — To draw the upper arm forward. 



Relations. — It is crossed ventrally by the pectoralis major, and dorsally it is in 

 relation with the tendons of the latissimus dorsi, the teres major, and the subscapu- 

 laris, from the last of which its tendon is separated by a mucous bursa {bursa m. 

 coraco-brachialis^. Laterally the muscle is in contact with the short head of the 

 biceps. It is usually pierced by the musculo-cutaneous nerve, and is in relation 

 medially with the axillary artery and the median and ulnar nerves. 



Variations. — Comparative anatomy shows that the coraco-brachialis is primarily an ex- 

 tensive muscle consisting of three portions, of which only the middle one and a part of the 

 inferior are normally present in man. The variations which occur usually consist in the 

 appearance of one or other of the missing portions. Thus the upper portion is sometimes 

 represented by a coj-aco-brachialis superior, which arises from the coracoid process and passes 

 laterally to be inserted into the lesser tuberosity of the humerus, or into the capsule of the 

 shoulder-joint, while the lower portion may be more completely represented by the insertion 

 of the muscle extending as far down as the medial epicondyle of the humerus. 



{b^ THE POST-AXIAL MUSCLES. 



I. Supraspinatus (Fig. 561). 



Attachments. — The supraspinatus occupies the supraspinous fossa of the 

 scapula, arising from the inner two-thirds of this and from the supraspinous fascia. 

 Its fibres pass laterally and converge to a tendon which is inserted into the upper facet 

 upon the greater tuberosity of the humerus and into the capsule of the shoulder- 

 joint. 



Nerve-Supply. — By the suprascapular nerve from the fifth and sixth cervical 

 nerves. 



Action. — To abduct the arm. 



The supraspinous fascia is the layer of connective tissue which covers the 

 supraspinatus muscle. It is attached to the superior border of the scapula above, to 

 the vertebral border medially, to the spine below, and gradually fades out laterally. 



