Brachiocephalic trunk, left common carotid artery, left subclavian artery
Mnemonic
“ABC”, from right to left:
- A - brachiocephalic Artery (innominate), which alone divides into the right common carotid and right subclavian
- B - left common carotid, Between the other two
- C - left subClavian
Three branches, but four vessels supplied, because the right side shares a common trunk while the left does not. This asymmetry follows the fate of the embryonic aortic arches, and it explains why a right subclavian steal presents differently from a left.
The left recurrent laryngeal nerve hooks under the arch at the ligamentum arteriosum, which is why it is affected by an arch aneurysm, a left hilar tumour or mitral stenosis.
Expansion
From right to left, in the order they leave the arch:
- Brachiocephalic trunk, which divides into the right common carotid and right subclavian arteries
- Left common carotid artery
- Left subclavian artery
The asymmetry is embryological: the right subclavian and right common carotid share a stem, while their left counterparts do not. The same asymmetry explains the different courses of the two recurrent laryngeal nerves.
The arch begins and ends at the level of the sternal angle, and the ligamentum arteriosum connects its inferior surface to the left pulmonary artery, hooking the left recurrent laryngeal nerve beneath it.