It usually arises from the costocervical trunk, which is a branch of the subclavian artery.

It is located distally to the vertebral artery and proximally to the costocervical trunk.

Costocervical trunk (truncus costocervicalis)

The deep portion anastomoses with the vertebral artery and with the a. profunda cervicalis, a branch of the costocervical trunk.

The 1st and 2nd posterior intercostal arteries arise from the supreme intercostal artery, a branch of the costocervical trunk of the subclavian artery.

It arises, in most cases, from the costocervical trunk, and is analogous to the posterior branch of an aortic intercostal artery: occasionally it is a separate branch from the subclavian artery.

The costocervical trunk arises from the upper and back part of the second part of subclavian artery, behind the scalenus anterior on the right side, and medial to that muscle on the left side.

The left subclavian artery and the right subclavian artery, one on each side of the body form the internal thoracic artery, the vertebral artery, the thyrocervical trunk, and the costocervical trunk.

The usual branches of the subclavian on both sides of the body are the vertebral artery, the internal thoracic artery, the thyrocervical trunk, the costocervical trunk and the dorsal scapular artery, the latter may branche off the transverse cervical artery which is a branch of the thyrocervical trunk.