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.
The Superior Profunda Artery arises a little beneath the conjoined tendons of the teres major and latissimus dorsi muscles, and then sinks, in company with the musculo-spiral nerve, into a canal formed by the three heads of the triceps muscle and the bone. From the back of the humerus it winds round to its outside in a spiral groove, which may be observed on that bone beneath the insertion of the deltoid muscle: here it divides into two branches, an anterior and posterior. The anterior pierces the external intermuscular ligament, and, accompanied by the musculo-spiral nerve, descends in a groove between the brachialis anticus and supinator longus muscles, to anastomose with the anterior radial recurrent artery. In this groove it is covered by the external cutaneous and musculo-spiral nerves, and still more superficially by the cephalic vein. The posterior branch descends in the substance of the triceps muscle, to which it sends numerous small branches, and terminates in anastomosing with the anterior branch and with the posterior interosseal and ulnar recurrents. The superior profunda artery is often very large, particularly when it arises from the posterior circumflex.