THE ANTERIOR PART OF THE NECK 153 



reaching the root of the neck, it curves laterally across the 

 dome of the pleura to the medial margin of the scalenus 

 anterior. The relations of the cervical part are somewhat 

 different from those on the right side. The same fascial 

 and muscular layers, and the same nerves and veins, are 

 anterior to it. Owing to its different direction, however, the 

 nerves and veins are placed more or less parallel to it. Three 

 additional relations are established viz., the phrenic nerve and 

 the left innominate vein lie anterior to it ; and the thoracic 

 duct first passes upwards in relation to its medial or right 

 side, and then arches over it to reach the angle of junction 

 between the subclavian and internal jugular veins (Fig. 55). 



The recurrent nerve on the left side hooks round the arch 

 of the aorta, and lies to the medial side of the subclavian 

 artery. 



Second Part. The second portion of the subclavian artery 

 forms the highest part or summit of the arch, and rises from 

 half an incr^ to an inch above the level of the clavicle. 



In that part of its course the vessel has not so many 

 superficial relations. Anteriorly, it is covered by (i) skin; 

 (2) superficial fascia and platysma; (3) deep fascia; (4) 

 clavicular head of the sterno-mastoid ; (5) scalenus anterior. 

 The phrenic nerve on the right side is also an anterior 

 relation, but it is separated from the artery by the medial 

 margin of the scalenus anterior. Posteriorly and inferiorly, 

 the vessel is in relation with the pleura, Sibson's fascia inter- 

 vening. The subclavian vein lies at a lower level than the 

 artery and on an anterior plane, and is separated from it 

 by the scalenus anterior. 



The third part of the subclavian artery is described on 

 p. 41. 



Branches of the Subclavian Artery. Four branches 

 spring from the subclavian trunk (Fig. 56). Three take 

 origin, as a general rule, from the first part of the artery, 

 and one from the second part. They are 



II. Vertebral. <- 

 ( Inferior thyreoid. 

 2. Thyreo-cervical. 1 Transverse cervical, 



i Transverse scapular. 

 3. Internal mammary. 



From the (, , /"Superior intercostal. 



second part. (Costo-cervical. (Deep cervical. 



In a great number of cases a branch of considerable size springs from 



