This section is from the book "Anatomy Of The Arteries Of The Human Body", by John Hatch Power. Also available from Amazon: Anatomy of the Arteries of the Human Body, with the Descriptive Anatomy of the Heart.
Anteriorly, besides by the integuments and pectoralis major muscle, it is covered by the union of the two roots of the median nerve, and for a very short distance by the nerve itself, which, however, inclines towards the outer side of the artery; at the lower part of this stage the artery is overlapped by the belly of the coraco-brachialis muscle.
Posteriorly, it rests against part of the tendon of the sub-scapularis muscle, and below this on the teres major and latissimus dorsi muscles, where it loses the name of axillary artery. Externally it is related to the lower part of the insertion of the sub-scapular tendon, to the external head of the median nerve, and to the external cutaneous nerve. Internally it corresponds to the internal head of the median, to the internal cutaneous and ulnar nerves, and to its own vein with the interposition of these nerves.
With regard to the relations between the axillary artery in its three stages, and the brachial plexus of nerves, we may repeat that in the first stage the brachial plexus is above and external to the artery; in about the middle of the second stage the termination or apex of the plexus forms a complete sheath around it; and in the third stage it has the branches of the plexus arranged around it in the following order: viz., in front, and crossing slightly to its outside, is the median nerve, and one or two slips uniting its roots; on the outside are the external cutaneous nerve and external head of the median; on the inside, the internal head of the median, and the internal cutaneous nerve lying on the ulnar; and posteriorly, the musculo-spiral and circumflex nerves.
This artery may be tied in its first and third stages; in the second stage, however, the operations must necessarily be attended with considerable difficulty, in consequence of its great depth from the surface and its close relation to the brachial plexus of nerves.