THE SUBCLAVIAN ARTERIES. 



417 



by the anterior scalenus muscle, forms the highest parb of the arch described by the 

 vessel across the root of the neck. Somewhat less deeply placed than the first part, 

 it is covered by the sberno-masboid and anterior scalenus muscles, with layers of 

 cervical fascia. Behind and below, it lies on the pleura. 



Relation to veins and nerves. The subclavian vein is farther forwards and lower 

 than the artery, and is separated from it by the anterior scalenus muscle. The 

 phrenic nerve, which descends obliquely inwards over that muscle, crosses the first 

 part of the subclavian artery of the left side close to the muscle, while on the right 

 side, not having quite reached the margin of the muscle at the level of the artery, it 

 is usually separated by the muscle from the second part of the artery. 



Fig. 349. VIEW OF THE RIGHT COMMON CAROTID AND SUBCLAVIAN ARTERIES, WITH THE ORIGIN OF 



THEIR BRANCHES AND THEIR RELATIONS. (R. Quain.) | 



For the explanation of the references in the upper part of this figure, see p. 389. The following 

 relate to the subclavian artery and its branches : 8, first part, 8', third part of subclavian artery ; 

 8", subclavian vein, shown by the removal of a portion of the clavicle ; 9, is placed on the scalenus 

 anticus, in the angle between the superficial cervical and suprascapular branches of the thyroid axis ; 

 10, outer part of the suprascapular artery ; 10', superficial cervical artery, passing into the deep surface 

 of the trapezius ; 10", posterior scapular artery, arising from the third part of the subclavian artery, 

 and passing through the brachial plexus of nerves and under the levator anguli scapulae; 11, on the 

 scalenus anticus, points to the inferior thyroid artery, near the place where the ascending cervical artery 

 is given off ; the phrenic nerve lies on the muscle to its outer side ; i y the suprasternal twig of the 

 suprascapular artery ; k, first rib ; I, perforating branch of internal mammary artery. 



