506 THE ARTERIES 



aorta. The pneumogastric nerve descends parallel to the artery between it and the 

 left common carotid, coming into contact with its anterior surface just before cross- 

 ing the arch of the aorta. The left cervical cardiac nerves of the sympathetic also 

 descend in front of it on their way to the cardiac plexus. The left common carotid 

 is situated anteriorly and to its right. The thoracic duct arches over the artery 

 just internal to the scalenus anticus, to empty its contents into the confluence of 

 the internal jugular and subclavian veins (fig. 360). 



Behind and somewhat internal to it are the ("esophagus, thoracic duct, inferior 

 cervical ganglion of the sympathetic, longus colli muscle, and vertebral column. 

 To some extent it is overlapped posteriorly by the left pleura and lung (fig. 328). 



On its right side are the trachea and the recurrent laryngeal nerve, and, higher 

 up, the oesophagus and thoracic duct. 



On its left side are the left pleura and lung. 



The chief variations in the origin of the left subclavian artery are given under Variations 

 OF THE Arch of the Aorta (page 472). 



THE FIRST PORTION OF THE RIGHT SUBCLAVIAN ARTERY 



The first portion of the right subclavian artery extends from its origin at 

 the bifurcation of the innominate, behind the upper margin of the right sterno- 

 clavicular joint, upwards and outwards in a gentle curve over the apex of the right 

 lung and pleura to the inner border of the scalenus anticus. It measures about 

 one inch and a quarter in length (3 cm.). In this course it ascends in the neck a 

 variable distance above the clavicle, but is so deeply placed, so surrounded by 

 important structures, and gives off so many large branches, that it is now seldom 

 or never selected for the application of a ligature. 



Relations. — In front it is covered by the integuments, the superficial fascia, 

 the platysma, the anterior layer of the deep fascia, the clavicular origin of tlie 

 sterno-mastoid, the sterno-hyoid and sterno-thyroid muscles, and the deep cervical 

 fascia. It is crossed by the commencement of the innominate, by the internal 

 jugular, and by the vertebral veins; and from within outwards by the pneumo- 

 gastric and phrenic nerves, and the superior cardiac branches of the sympathetic 

 nerve. A loop of the sympathetic nerve itself also crosses the arter}^ and forms 

 with the trunk of the sympathetic a ring around the vessel known as the annulus 

 of Vieussens. 



Behind, but separated from the artery by a cellular interval, are the longus 

 colli muscle, the transverse process of the seventh cervical or first thoracic vertebra, 

 the main chain of the sympathetic nerve, the inferior cardiac nerves, the recurrent 

 laryngeal nerve, and the apex of the right lung and pleura. 



Below, it is in contact with the pleura and lung and the loop of the recurrent 

 laryngeal nerve, wdiich winds round the artery from the pneumogastric and ascends 

 behind it to the larynx. The subclavian vein is below^ the artery and on an anterior 

 plane. 



Branches. — The vertebral, internal mammary, and thyroid axis arise from this 

 part of the vessel. Not uncommonly a small al)errant artery also takes origin from 

 this portion of the artery and descends to the left 1:)ehind the oesophagus to join a 

 branch of the aorta opposite the third or fourth thoracic vertebra. This vessel is 

 probably the remains of the right aortic root. 



THE SECOND PORTION OF THE SUBCLAVIAN ARTERY 



The second portion of the subclavian artery lies behind the scalenus anticus 

 muscle. It measures about three-quarters of an inch in length (2 cm.), and here 

 reaches liighest in the neck. The subclavian vein is separated from tlie artery by 

 the scalenus anticus, and lies on a lower and anterior plane. 



Relations. — In front it is covered by the skin, superficial fascia, platysma, 

 anterior layer of deep fascia, the clavicular origin of the sterno-mastoid, posterior 



