In regard to flexion of the thumb, only the flexor pollicis longus is located in the forearm. It lies beside the flexor profundus and is attached to the distal phalanx (digit) just as the flexor profundus.
It originates on the anterior surface of the middle half of the radius and adjacent parts of the interosseous membrane.
Insertion is on the anterior surface of the base of the distal phalanx of the thumb.
Flexes the fingers.