It is crossed by the internal jugular vein and the vertebral vein, by the vagus nerve and the cardiac branches of the vagus and sympathetic, and by the subclavian loop of the sympathetic trunk which forms a ring around the vessel.

[1][3] It ascends in the superior mediastinal cavity to the root of the neck, and then arches lateralward to the medial border of the scalenus anterior muscle.

Behind, it is in relation with the esophagus, thoracic duct, left recurrent laryngeal nerve, inferior cervical ganglion of the sympathetic trunk, and the longus colli muscle; 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 laryngeal nerve.

On the right side of the neck, the phrenic nerve is separated from the second part of the artery by the scalenus anterior muscle, while on the left side it crosses the first part of the artery close to the medial edge of the muscle.

[4] 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.

The terminal part of the artery lies behind the clavicle and the Subclavius and is crossed by the transverse scapular vessels.

Behind, it lies on the lowest trunk of the brachial plexus, which intervenes between it and the scalenus medius muscle.

[1][4]From its origin to the medial border of scalenus anterior Lying behind scalenus anterior Between the lateral border of scalenus anterior and the outer border of the first rib Embryologically, the left subclavian simply arises from the left 7th intersegmental artery,[5] while the right subclavian arises, proximal to distal: Essentially, the 4th aortic arch and dorsal aorta form the aortic arch on the left, but since the right dorsal aorta regresses distal to the right 7th intersegmental artery, on the right they form the proximal portion of the subclavian artery.

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.

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 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.

[9] This article incorporates text in the public domain from page 575 of the 20th edition of Gray's Anatomy (1918) ocular group: central retinal