The Axillary Nerve (n. axillaris; circumflex nerve) arises from the posterior cord of the brachial plexus, and its fibers are derived from the fifth and sixth cervical nerves.
t lies at first behind the axillary artery, and in front of the Subscapularis, and passes downward to the lower border of that muscle.
It then winds backward, in company with the posterior humeral circumflex artery, through a quadrilateral space bounded above by the Subscapularis, below by the Teres major, medially by the long head of the Triceps brachii, and laterally by the surgical neck of the humerus, and divides into an anterior and a posterior branch.
- The anterior branch (upper branch) winds around the surgical neck of the humerus, beneath the Deltoideus, with the posterior humeral circumflex vessels, as far as the anterior border of that muscle, supplying it, and giving off a few small cutaneous branches, which pierce the muscle and ramify in the skin covering its lower part.
- The posterior branch (lower branch) of the axillary nerve supplies the Teres minor and the posterior part of the Deltoideus; upon the branch to the Teres minor an oval enlargement (pseudoganglion) usually exists. The posterior branch then pierces the deep fascia and is continued as the superior lateral brachial cutaneous nerve, which sweeps around the posterior border of the Deltoideus and supplies the skin over the lower two-thirds of the posterior part of this muscle, as well as that covering the long head of the Triceps brachii
The trunk of the axillary nerve gives off an articular filament which enters the shoulder-joint below the Subscapularis.