THE SUBCLA VIAN ARTERY 627 



First Part of the Left Subclavian Artery (Figs. 431 and 432). The first 

 part of the left subclavian artery arises frjm the arch of the aorta, behind the 

 left common carotid, and at the level of the fourth thoracic vertebra; it ascends 

 nearly vertically to the root of the neck and then arches outward to the inner 

 margin of the Scalenus anticus muscle. 



Relations. It is in relation, in front, with the vagus, cardiac, and phrenic nerves, which 

 lie parallel with it, the left carotid artery, left internal jugular and vertebral veins, and the com- 

 mencement of the left innominate vein, and is covered by the Sternothyroid, Sternohyoid, and 

 Sternomastoid muscles. A loop of the sympathetic encircles the artery, forming the ansa sub- 

 clavia. Behind, it is in relation with the oesophagus, thoracic duct, inferior cervical ganglion 

 of the sympathetic, and Longus colli muscle; higher up, however, the oesophagus and thoracic 

 duct lie to its right side; the latter ultimately arching over the vessel to join the angle of union 

 between the subclavian and internal jugular veins. To its inner side are the o?sophagus, trachea, 

 thoracic duct, and left recurrent laryngeal nerve; to its outer side, the left pleura and lung. 



PLAN OF THE RELATIONS OF FIRST PORTION OF THE LEFT SUBCLAVIAN ARTERY. 



In front. 



Vagus, cardiac, and phrenic nerves. 

 Left carotid artery. 

 Thoracic duct. 



Left internal jugular, vertebral, and innominate veins. 

 Sternothyroid, Sternohyoid, and Sternomastoid muscles. 

 Inner side. / ~^\ 



/ \ Outer side. 



Trachea. / Left \ 



(Esophagus. I JSJ* 1 1 Pleura and left lung. 



Thoracic duct. V J 



Left recurrent laryngeal nerve. ^^__^/ 



Behind. 



(Esophagus and thoracic duct. 

 Inferior cervical ganglion of sympathetic. 

 Longus colli. 



Second and Third Parts of the Subclavian Artery (Figs. 4^5 and 457). 

 The second portion of the subclavian artery lies behind the Scalenus anticus muscle; 

 it is very short, and forms the highest part of the arch described by that vessel. 



Relations. It is covered, in front, by the skin, superficial fascia, Platysma, deep cervical 

 fascia, the Sternomastoid and the Scalenus anticus muscles. On the right side the phrenic 

 nerve is separated from the second part of the artery by the Scalenus anticus muscle, while on 

 the left side the nerve crosses the first part of the artery immediately to the inner edge of the 

 muscle. Behind, it is in relation with the pleura and the Scalenus medius muscle. Above, is 

 the brachial plexus of nerves; below, the pleura. The subclavian vein lies below and in front 

 of the artery, separated from it by the Scalenus anticus muscle. 



PLAN OF THE RELATIONS OF SECOND PORTION OF SUBCLAVIAN ARTERY. 



In front. 



Skin and superficial fascia. 

 Platysma and deep cervical fascia. 

 Sternomastoid. 

 Phrenic nerve. 

 Scalenus anticus. 

 Subclavian vein. 



Above. I Subclavian \ Below. 



I Artery. 



Brachial plexus. I second J Pleura. 



Behind. 

 Pleura and Middle Scalenus. 



