Long thoracic n.

The long thoracic nerve supplies motor innervation to the serratus anterior m. This nerve characteristically arises by three roots from the fifth, sixth, and seventh cervical nerves (C5-C7) but the root from C7 may be absent. The roots from C5 and C6 pierce the medial scalene m., while the C7 root passes in front of the muscle.

The nerve descends behind the brachial plexus and the axillary vessels along the external surface of the serratus anterior m. supplying small branches to each of its finger-like projections.