The organization of the upper limb is based on compartments. All the details will follow, but before getting into the specifics it helps to have an overview of these compartments. When you lose a nerve, you typically lose a compartment, or two, and if you know the function of that compartment then the nerve palsies are easier to understand. Both the arm and forearm each have anterior and posterior compartments. The posterior arm and posterior forearm are radial nerve territory, the anterior arm is musculocutaneous nerve territory, and the anterior forearm is innervated by the median nerve except for one and a half muscles—the flexor carpi ulnaris, and half of flexor digitorum profundus. And in the hand the median nerve innervates three-and-a-half muscles, and the ulnar innervates everything else.