The macaque multitendoned extrinsic finger muscles--extensor digitorum communis, extensor digitorum quarti et quinti proprius, extensor digitorum secundi et tertii proprius, flexor digitorum superficialis and flexor digitorum profundus (FDP)--were studied to define their muscle fiber architecture, tendon structures, endplate bands and patterns of external and internal nerve branching. Muscle fiber architecture was then used to define regions in each muscle that might represent functional subdivisions. Only in the FDP were these regions innervated by primary nerve branches characteristic of neuromuscular compartments.