THE HEART AND VASCULAR SYSTEM. i9 



below that muscle. It passes through the space known as the 

 axilla (vide Regions). 



Relations. First portion: The first portion of the subclavian is in 

 relation in front with the subclavius and pectoralis major muscles, 

 costo-coracoid membrane, and acromial thoracic and cephalic veins, and 

 the external anterior thoracic nerve; the axillary vein to its inner side, 

 the brachial plexus to its outer side, and the posterior thoracic nerve 

 and serratus magnus behind. Second portion: The relations of the 

 second portion are much the same as the first, with the addition of the 

 pectoralis minor in front and the division of the brachial plexus sur- 

 rounding the vessel. Third portion: The third portion is in relation in 

 front with the inner head of the median nerve and the pectoralis major 

 muscle; to the inner side with the axillary vein, internal cutaneous and 

 ulnar nerves; to the outer side, the median and musculo-cutaneous 

 nerves and coraco-brachialis muscle; and, behind, the circumflex and 

 musculo-spiral nerves and the subscapularis, latissiinus dorsi, and teres 

 major muscles. 



Its branches are: 



Superior thoracic, supplies the pectoralis major and minor 

 muscles ; 



Acromial thoracic, gives off three branches acromial, tho- 

 racic, and descending, supplying the pectoralis major, minor, 

 serratus, and deltoid; 



Long thoracic follows the lower border of the pectoralis 

 minor to supply the serratus, pectoralis major and minor, and 

 mammary glands ; 



Alar thoracic supplies the axillary glands ; 



Subscapular, arises from the axillary artery about the level 

 of the lower border of the subscapularis muscle. It passes 

 backward and downward to the inferior dorsum of the scapula. 

 Its branches anastomose with the posterior scapular and the 

 suprascapular. They are: 



Subscapular, supplies the subscapularis muscle; 



Dorsalis scapulae, is distributed to the infraspinous fossa, anasto- 

 mosing with the posterior scapular and suprascapular arteries; 



Median branch, descends the axillary border of the scapula to 

 supply teres muscles. 



Posterior circumflex, encircles the neck of the humerus to 

 supply the shoulder- joint and the deltoid muscle; 



Anterior circumflex, descends beneath the short head of 

 biceps and coraco-brachialis muscles to supply the shoulder-joint. 



THE BRACHIAL ARTERY 



commences at the lower border of the latissimus dorsi and teres 

 major muscles and descends on the front and inner aspect of the 

 arm to half an inch below the in id die of a line drawn through 



