The posterior compartment of the arm contains the triceps muscle, which has three heads that originate on the scapula and humerus and insert into the ulna. The triceps is innervated by the radial nerve and supplied by the profunda brachii artery. The radial and ulnar nerves also pass through this compartment, with the radial nerve giving motor branches to the triceps and surrounding muscles and the ulnar nerve accompanied by the superior ulnar collateral vessels.