musculus flexor pollicis brevis

[TA] short flexor muscle of thumb (2 heads): origin, CAPUT SUPERFICIALE—flexor retinaculum, distal part of tubercle of trapezium, CAPUT PROFUNDUM—trapezoid and capitate bones and palmar ligaments of distal row of carpal bones; insertion, radial side of base of proximal phalanx of thumb; innervation, median, ulnar; action, flexes and adducts thumb. The deep head varies considerably in size and may be absent.