[2] It arises from the grooved anterior (side of palm) surface of the body of the radius,[3] extending from immediately below the radial tuberosity and oblique line to within a short distance of the pronator quadratus muscle.

[5] It arises also from the adjacent part of the interosseous membrane of the forearm, and generally by a fleshy slip from the medial border of the coronoid process of the ulna.

[6] The fibers end in a flattened tendon, which passes beneath the flexor retinaculum of the hand through the carpal tunnel.

In orangutans there is a tendon similar in insertion and function to the FPL in humans, but which has an intrinsic origin on the oblique head of the adductor pollicis.

[10] Lesser apes (i.e. gibbons) and Old World monkeys (e.g. baboons) share an extrinsic FPL muscle tendon with humans.