The upper limb is supplied by nerves from the brachial plexus. Above the clavicle the fifth, sixth and seventh nerves send branches to adjacent muscles. The suprascapular is the largest branch given off above the clavicle.

Below the clavicle the three cords give off branches. The three sub-scapulars, the circumflex and musculo-spiral nerves arise from the posterior cord.

The musculo-spiral is the largest branch of the plexus. It passes under the axillary artery, and between the inner and outer heads of the triceps muscle, reaches the musculo-spiral groove, winds through it to the outer side of the arm, where it divides into the radial and posterior interosseus, which go down the back of the. forearm and hand.

The external anterior thoracic, musculo-cutaneous and outer head of median arise from the outer cord.

The musculo-cutaneous passes down between the biceps and brachialis anticus to the elbow, where it divides into anterior and posterior branches.

The internal anterior thoracic, internal cutaneous, ulnar and inner head of median arise from the inner cord.

The ulnar is the largest branch of the inner cord ; it passes along the inner side of the arm till it reaches the space between the internal condyle and the olecranon, when it enters the forearm and goes straight to the wrist and hand.

The median arises from inner and outer cords. It passes down the inside of the arm to the elbow, and enters the forearm between the two heads of the pronator radii teres. It proceeds down the middle of the forearm and terminates in the hand.

In emerging from the axilla the cords accompany the artery.