[The interosseous palmaris muscle of the thumb. Results of an anatomic study of a muscle of the first ray].

In sixteen of twenty adult human cadaveric hands a muscle fascicle was isolated from the adductor pollicis muscle. It had osseous origins from the base of the first metacarpal bone and from the trapezium bone in eleven hands. These origins were connected by a fibrous arch, which was a soft tissue origin itself. In two of the sixteen hands, muscle fibers emerged from the palmar aspect of the first dorsal interosseous muscle near the radial artery. The findings can be explained by the ontogenesis of the human hand. The described muscle is neither a part of the oblique head of the adductor pollicis nor an equivalent to the three palmar interosseous muscles. In our dissections it was a constant muscle. Other studies have to show the exact function of the muscle. We postulate a stabilization of the carpometacarpal joint of the thumb.