In 1813 Gantzer described 2 accessory muscles in the human forearm which bear his name (Wood, 1868; Macalister, 1875; Testut, 1884; Le Double, 1897). The more frequent of the 2 accessory muscles or ‘accessorius ad pollicem’ was found to arise from the coronoid process of the ulna, coursing distally to attach into the flexor pollicis longus muscle (flexor pollicis longus accessory head, FPLah). The less frequently observed or ‘accessorius ad flexorem profundum digitorum’ was again found to arise from the coronoid process and course to join into the flexor digitorum profundus (flexor digitorum profundus accessory head, FDPah). Since their initial description, they have been examined in further detail by a number of authors (Wood, 1868; Macalister, 1875; Le Double, 1897; Dykes & Anson, 1944; Mangini, 1960; Malhotra et al. 1982; Dellon & McKinnon, 1987; Kida, 1988). These studies, most of them focusing on the FPLah, all show different results of prevalence, origin, insertion, relations and nerve supply. We undertook this study with the aim of providing a more accurate account of the detailed morphology of both accessory muscles because of the above-mentioned inconsistent anatomical descriptions and the lack of information as to important aspects such as vascular supply, morphology (shape and length) and the coexistence of both accessory heads.