Homology of the adductor pollicis and contrahentes muscles: a study of monkey hands.

The deep palmar muscles in monkey hands were studied. The contrahentes muscles mainly arose from the capitate bone, descended palmar to the deep palmar branch of the ulnar nerve and the palmar metacarpophalangeal nerves, and attached to the proximal phalanges or wing tendons of the second, fourth and fifth fingers. In relation to the deep palmar branch of the ulnar nerve and the palmar metacarpophalangeal nerves, the contrahentes muscles are homologous with the adductor pollicis and flexor indicis radialis muscles. The contrahentes muscles occasionally gave off some accessory slips which blended with the interosseous muscles. These findings suggest that the human adductor pollicis muscle is a well-developed remnant of a contrahens muscle, and that the human interosseous muscles contain some remnant of the contrahentes muscle. In fact, a well-developed remnant of a contrahens muscle was found in the fourth finger of a human hand. It is further considered that the human adductor pollicis muscle contains an element of the interosseous muscle of the thumb.