Brachial plexus

The brachial plexus is formed by the ventral rami of the lower cervical and upper thoracic nerve roots. It is cephalad and posterior to the subclavian artery as it passes posterior to the first rib. The trunks of the brachial plexus (superior [C5,C6], middle [C7], inferior [C8,T1]) pass between the anterior and middle scalene muscles.