THE ANTERIOR PART OF THE NECK 151 



end of the internal jugular vein and the common carotid 

 artery ; the remainder can be seen if the internal jugular vein 

 is drawn aside. On the left side, the first part of the artery is 

 concealed by the commencement of the innominate vein, which 

 must be pushed aside. On both sides, the second part of 

 the artery lies posterior to the scalenus anterior, which must 

 be left in position. 



The subclavian artery is the first portion of the great 

 arterial trunk which carries blood for the supply of the upper 

 extremity. It arises differently on the two sides of the body. 

 On the right side, it takes origin, behind the sterno-clavicular 

 joint, as a terminal branch of the innominate artery. On 

 the left side, it arises from the aortic arch, in the superior 

 mediastinum. In both cases, it takes an arched course 

 laterally across the root of the neck, posterior to the scalenus 

 anterior and on the anterior surface of the cervical dome of 

 pleura, a short distance below its summit. At the outer 

 border of the first rib it becomes the axillary artery. 



For descriptive purposes the artery is divided into three 

 parts. The first part extends from the origin of the vessel 

 to the medial margin of the scalenus anterior ; the second 

 portion lies posterior to that muscle ; and the third part 

 extends from the lateral border of the scalenus anterior to 

 the outer border of the first rib. 



First Part. Owing to the difference of origin, the relations 

 of the first portion of the subclavian artery are not the same 

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

 subclavian 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 arid 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 

 in 1 c 



