31 cadaver arms have been dissected to study the variations in the anatomy of the muscles and fibrous arches which might cause compression of the median nerve in the forearm. Pronator teres always had a superficial head and usually a deep head. Flexor digitorum superficialis varied greatly in its site of origin. The median nerve might be crossed by two, one or no fibro-aponeurotic arches. Gantzer's muscle, an accessory head of flexor pollicis longus, was present in 45% of cadavers. No ligament of Struthers was found. Possible sites and causes of nerve compression are discussed.