NCIt definition : A muscle in the hand that has a superficial head that originates from the flexor retinaculum
and tubercle of the trapezium bone and a deep head that originates from the trapezoid
and capitate bones; it attaches to the lateral side of the base of the proximal phalanx
of the thumb and functions to flex the thumb at the metacarpophalangeal joint.;
Alternative definition : CDISC: A muscle of the hand, whose superficial head extends from the flexor retinaculum
and tubercle of the trapezium bone and deep head that extends from the trapezoid and
capitate bones, extending to the lateral side of the base of the proximal phalanx
of the thumb; primary function is to flex the thumb at the metacarpophalangeal joint.;