The interosseous and lumbrical muscles in the human hand, with special reference to the insertions of the interosseous muscles.

The interosseous and lumbrical muscles in twenty-five hands of Japanese adult cadavers were dissected. The palmar and dorsal interosseous muscles continued, with few exceptions, into the wing tendons. The dorsal interosseous muscles gave off tendons which pierced the transverse laminae or passed deep to the transverse laminae, and attached to the bases of the proximal phalanges. The palmar interosseous muscles seldom had such attachments. The palmar and dorsal interosseous muscles sometimes gave off additional tendons which passed superficial to the transverse laminae and attached to the bases of the proximal phalanges. These latter attachments were typical in the contrahentes muscles. Thus, the present findings suggest that the human dorsal interosseous muscles are composite muscles derived from the dorsal abductor, flexor brevis and contrahens muscles, and that the human palmar interosseous muscles are composite muscles derived from the flexor brevis and contrahens muscles. The lumbrical muscles rarely gave off accessory slips with atavistic attachments to the proximal phalanges.