Architecture
Five roots become three trunks in the scalene interval, each trunk splits into anterior and posterior divisions behind the clavicle, and the divisions reassemble into three cords named for their relation to the axillary artery.
Surface projection
The plexus is closest to the surface in the supraclavicular fossa. Distally its terminal branches — axillary, radial, median, ulnar and musculocutaneous — each carry their own recognisable cutaneous field.