Within a period of five months, in eleven of all the cases examined, the author found the M. abductor digiti minimi longus as was described by Frohse and Fränkel in 1908. It ran from the fascia antebrachii through the Canal de Guyon to the hypothenar muscle mass. Vascularization and innervation were by the ulnar artery and nerve. This muscle must be assigned to the hypothenar muscular system, while a variation of the palmaris longus muscle, which is found in the same region and frequently described in the literature is supplied by the median nerve. Further, the literature has held this muscle to be the cause of compression of the ulnar nerve. In the author's view, the compression of the nerve is caused by the distal transverse ligament of the fascia antebrachii. By severing this transverse ligament, regeneration of the nerve is made possible.