Insertions of the lumbrical and interosseous muscles in the human foot.

The lumbrical and interosseous muscles in twenty-five feet of Japanese adult cadavers were dissected. The lumbrical muscles mainly continued into the dorsal aponeuroses or the terminal tendons of the extensor digitorum longus muscle, though they occasionally issued some accessory and slender tendons inserting into the bases of the proximal phalanges. Rarely, the lumbrical muscle showed an atavistic anomaly. In this anomaly, the lumbrical muscle was divided into two tails which continued into the bases of the proximal phalanges of the contiguous toes. The plantar and dorsal interosseous muscles were mainly attached to the bases of the proximal phalanges. Frequently, the plantar and dorsal interosseous muscles issued some accessory and small tendons continuing into the dorsal aponeuroses. This fact suggests that the plantar and dorsal interosseous muscles in the foot, like the palmar and dorsal interosseous muscles in the hand, are composite muscles derived from the flexor brevis, contrahens and other muscles.