250 HEAD AND NECK 



on the two sides of the body. The first part of the right 

 subdavian extends obliquely upwards and laterally, and at its 

 termination at the medial margin of the scalenus anterior 

 it has reached a point above the level of the clavicle. It is 

 placed very deeply. Anteriorly, it is covered by the skin, 

 superficial fascia, platysma, deep fascia, and three muscular 

 strata viz., the clavicular origin of the sterno-mastoid, the 

 sterno-hyoid, and the sterno-thyreoid. Three veins and some 

 nerves are placed anterior to it. At the medial margin of 

 the scalenus anterior it is crossed by the internal jugular 

 and vertebral veins, whilst the anterior jugular vein, as it 

 passes laterally under cover of the sterno-mastoid, is separated 

 from it by the sterno-hyoid and sterno-thyreoid muscles. The 

 nerves which cross anterior to it are the vagus, a loop from 

 the sympathetic (ansa subclavia), and in some cases cardiac 

 branches of the vagus and sympathetic as they run to the 

 thorax. At the lower margin of the artery the vagus nerve 

 gives off its recurrent branch. 



The cervical dome of the pleura is both below and posterior 

 to the artery, and the recurrent branch of the vagus nerve 

 hooks round below and ascends posterior to it. 1 



On the left side, the first part of the subclavian ascends 

 almost vertically from its origin from the aortic arch, and, 

 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. 



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 



1 If the lung has been removed by the dissector of the thorax the lower 

 and posterior relations should be verified by examination from the thoracic 

 side. 



