Lateral intermuscular septum

The lateral intermuscular septum extends from the lower part of the crest of the greater tubercle of the humerus, along the lateral supracondylar ridge, to the lateral epicondyle; it is blended with the tendon of the Deltoideus, gives attachment to the Triceps brachii behind, to the Brachialis, Brachioradialis, and Extensor carpi radialis longus in front, and is perforated by the radial nerve and profunda branch of the branchial artery.