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Other Terms: Circumflex humeral nerve, Nervus axillaris, Nerf axillaire
The axillary nerve arises from the posterior cord of the brachial plexus, passes downward and laterally behind the third portion of the axillary artery. It then turns around the lower border of the subscapularis muscle to the quadrilateral subdivision of the subscapular triangle. At this point, with the posterior circumflex artery, it leaves the axilla. Between the axillary border of the scapula and the teres minor, it gives off an articular branch which pierces the capsular ligament to supply the shoulder joint. Then it divides into a superior and an inferior branch. The superior branch, the lateral cutaneous nerve of the arm, accompanies the posterior circumflex artery around the back of the surgical neck of the humerus and under the deltoid to its anterior border, supplying this muscle and the skin over its lower part. The inferior or muscular branch sends several branches to the back part of the deltoid. It also sends one branch, which has a gangliform enlargement due to a thickening of fibrous tissue on its trunk, to the teres minor. After this, it passes under the deltoid and around the lower part of its posterior border to supply the skin over the long head of the triceps and the lower two-thirds of the posterior part of the deltoid. A bicipital branch arises from the end of the axillary nerve and passes up the intertubercular groove to supply the tendon of the long head of the biceps, the proximal end of the humerus, and the shoulder joint. In luxation of the humerus, the axillary nerve is sometimes stretched over the head of the humerus, and paralysis of the deltoid may ensue.