From its origin, the subclavian artery travels laterally, passing between anterior and middle
scalene muscles, with the
anterior scalene on its anterior side and the
middle scalene on its posterior. This is in contrast to the
subclavian vein, which travels anterior to the anterior scalene. As the subclavian artery crosses the lateral border of the
first rib, it becomes the
axillary artery. On the right side, the subclavian artery arises from the brachiocephalic (innominate) artery behind the right sternoclavicular articulation; on the left side it springs from the arch of the aorta. The left subclavian artery is around 9
cm long in
adults, while the right subclavian artery is around 6 cm long. • The second part, also known as the scalene part, It passes upward and lateralward to the medial margin of the
scalenus anterior muscle. It ascends a little above the medial part of the
clavicle. while the right subclavian arises, proximal to distal: • right 4th
aortic arch • right
dorsal aorta • right 7th intersegmental artery 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. Since the left subclavian is then a tributary of the left common carotid, they can be thought of as arising from the brachiocephalic trunk.
Variation 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 anterior scalene; 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 common carotid artery, forming a left brachiocephalic trunk. 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 sternocleidomastoid corresponds pretty closely to the lateral border of the anterior scalene, so that the third portion of the artery, the part most accessible for operation, lies immediately lateral to the posterior border of the sternocleidomastoid. Some authors describe the subclavian artery as arising from the 7th intersegmental artery. == Function ==