Anatomical study on the extensor digitorum profundus muscle in the Japanese.

An anatomical study on the extensor digitorum profundus muscle was made using 832 upper limbs from 416 Japanese adults. The separate muscles derived from the extensor digitorum profundus consist of 10 kinds: namely, the extensor pollicis longus, extensor pollicis et indicis accessorius, extensor indicis radialis, extensor indicis proprius, extensor indicis ulnaris, extensor indicis et medii accessorius, extensor medii proprius, extensor annularis proprius, extensor carpi profundus and extensor digiti brevis. The configuration of the muscles (except for the extensor digiti brevis) in the upper limb was classified into 13 types according to their arrangement and insertion. The most frequent type involved coexistence of the extensor pollicis longus and the extensor indicis proprius: it was observed in 664 limbs (79.8%). The next type involved coexistence of the extensor pollicis longus, extensor indicis proprius and the extensor medii proprius: it was observed in 67 limbs (8.1%). It appears that the extensor digiti brevis of man is derived from the most ulnar part of the extensor digitorum profundus which does not migrate proximally.