Relationship of radial nerve to brachialis and supinator muscles

In the cubital fossa, lateral to the brachialis, the radial nerve divides into deep (motor) and superficial (sensory) branches. The deep branch penetrates the supinator muscle and emerges in the posterior compartment of the forearm as the posterior interosseous nerve. It joins the artery of the same name to run in the plane between the superficial and the deep extensors of the forearm.