ARTERY 



First Part of the Left Subclavian Artery (Fig. 505). The first part of the left 

 subclavian artery arises from the arch of the aorta, behind the left common carotid, 

 and at the level of the fourth thoracic vertebra; it ascends in the superior medias- 

 tinal cavity to the root of the neck and then arches lateralward to the medial 

 border of the Scalenus anterior. 



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

 parallel with it, the left common carotid artery, left internal jugular and vertebral veins, and 

 the commencement of the left innominate vein, and is covered by the Sternothyreoideus, Sterno- 

 hyoideus, and Sternocleidomastoideus; behind, it is in relation with the esophagus, thoracic 

 duct, left recurrent nerve, inferior cervical ganglion of the sympathetic trunk, and Longus colli; 

 higher up, however, the esophagus 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. Medial to it are the esophagus, trachea, thoracic duct, and left recurrent nerve; lateral 

 to it, the left pleura and lung. 



Second and Third Parts of the Subclavian Artery (Fig. 520). The second 

 portion of the subclavian artery lies behind the Scalenus anterior; it is very short, 

 and forms the highest part of the arch described by the vessel. 



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

 fascia, Sternocleidomastoideus, and Scalenus anterior. On the right side of the neck the 

 phrenic nerve is separated from the second part of the artery by the Scalenus anterior, while 

 on the left side it crosses the first part of the artery close to the medial edge of the muscle. 

 Behind the vessel are the pleura and the Scalenus medius; above, 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 anterior. 



The third portion of the subclavian artery runs downward and lateralward from 

 the lateral margin of the Scalenus anterior to the outer border of the first rib, 

 where it becomes the axillary artery. This is the most superficial portion of the 

 vessel, and is contained in the subclavian triangle (see page 565). 



Relations. It is covered, in front, by the skin, the superficial fascia, the Platysma, the supra- 

 clavicular nerves, and the deep cervical fascia. The external jugular vein crosses its medial 

 part and receives the transverse scapular, transverse cervical, and anterior jugular veins, which 

 frequently form a plexus in front of the artery. Behind the veins, the nerve to the Subclavius 

 descends in front of the artery. The terminal part of the artery lies behind the clavicle and the 

 Subclavius and is crossed by the transverse scapular vessels. The subclavian vein is in front 

 of and at a slightly lower level than the artery. Behind, it lies on the lowest trunk of the brachial 

 plexus, which intervenes between it and the Scalenus medius. Above and to its lateral side are 

 the upper trunks of the brachial plexus and the Omohyoideus. Below, it rests on the upper 

 surface of the first rib. 



Peculiarities. The subclavian arteries vary in their origin, their course, and the height to 

 which they rise in the neck. 



The origin of the right subclavian from the innominate takes place, in some cases, above the 

 sternoclavicular articulation, and occasionally, but less frequently, below that joint. The artery 

 may arise as a separate trunk from the arch of the aorta, and in such cases it may be either the 

 first, second, third, or even the last branch derived from that vessel; in the majority, however, 

 it is the first or last, rarely the second or third. When it is the first branch, it occupies the ordinary 

 position of the innominate artery; when the second or third, it gains its usual position by passing 

 behind the right carotid; and when the last branch, it arises from the left extremity of the arch, 

 and passes obliquely toward the right side, usually behind the trachea, esophagus, and right 

 carotid, sometimes between the esophagus and trachea, to the upper border of the first rib, 

 whence it follows its ordinary course. In very rare instances, this vessel arises from the thoracic 

 aorta, as low down as the fourth thoracic vertebra. Occasionally, it perforates the Scalenus 

 anterior; more rarely it passes in front of that muscle. Sometimes the subclavian vein passes 

 with the artery behind the Scalenus anterior. The artery may ascend as high as 4 cm. above 

 the clavicle, or any intermediate point between this and the upper border of the bone, the right 

 subclavian usually ascending higher than the left. 



The left subclavian is occasionally joined at its origin with the left carotid. 



The left subclavian artery is more deeply placed than the right in the first part of its course, 

 and, as a rule, does not reach quite as high a level in the neck. The posterior border of the Sterno- 

 cleidomastoideus corresponds pretty closely to the lateral border of the Scalenus anterior, so 

 that the third portion of the artery, the part most accessible for operation, lies immediately 

 lateral to the posterior border of the Sternocleidomastoideus. 

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