[Fascicular arrangement. Function and innervation of the 1st dorsal interosseous muscle of the hand].

After 30 dissections done under optical magnification, the authors have shown that, the tendon of the first dorsal interosseous muscle, which was till now considered to be bifasciculare results actually from the intersection of the tendinous fibers of three muscle components: One originating from the first metacarpal bone: Heterometacarpophalangeal component. One originating from the first two metacarpal bones: Intermediate component. One originating from the second metacarpal bone: Homometacarpophalangeal component. Each of these musculotendinous components is responsible for a particular action in the different movements of the index finger: Flexion of the metacarpophalangeal joint, extension of the second and third phalanges, abduction of the index finger. Each component has its own nerve supply by branches originating from deep branch of the ulnar nerve. In total, there exists a "rule of the three". Three components--Three principal actions--Three nerve supply.