[Muscle anomalies of the upper extremity as an atavistic cause of peripheral nerve disorder].

We report on 2 patients with anomalous muscles of the upper extremity causing symptoms of peripheral nerve entrapment. Our first case clinically showed a lesion of the R. dorsalis manus of nervus ulnaris produced by an accessory muscle belly at the dorsum of the hand to be identified as an extensor indicis brevis muscle. The second case presented a carpal-tunnel-syndrome, tunnel into the palm. Phylogenetically and ontogenetically these muscles are classified as atavistic. We demonstrate the homologies of the upper extremity of fishes, amphibians, reptiles, lower mammals and man, which show an upward migration of the muscle masses from the hand to the forearm. By that means the upper extremity gains additionally to the power of the reptiles paw the functionality and free motility of the human hand.