Transverse section of posterior interosseous nerve from a case of lead poisoning showing increased connective tissue

The posterior interosseous nerve (also called the dorsal interosseous nerve) is the continuation of the deep branch of the radial nerve after it penetrates the supinator muscle. It carries fibers from the C7 and C8 spinal roots and supplies most of the muscles in the posterior compartment of the forearm. (Source: Oliver T. Lead poisoning in its acute and chronic forms: The Goulstonian Lectures, delivered in the Royal College of Physicians, March 1891. Edinburgh and London: Young J. Pentland, 1891. Public domain.)