Flexor pollicis longus muscle

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Flexor pollicis longus muscle
Front of the left forearm. Deep muscles. (Flexor pollicis longus is shown in blue)
Latin musculus flexor pollicis longus
Gray's subject #125 449
Origin: The middle 2/4 of the volar surface of the radius and the adjacent interosseus membrane. (Also occasionally a small origin slightly on the medial epicondyle of the ulna.)
Insertion: The base of the distal phalanx of the thumb
Artery: Anterior interosseus artery
Nerve: Anterior interosseous nerve (branch of median nerve) (C8, T1)
Action: Flexion of the thumb.
Antagonist: Extensor pollicis longus muscle, Extensor pollicis brevis muscle
Dorlands/Elsevier m_22/12549138

The flexor pollicis longus is a muscle in the forearm and hand that flexes the thumb. It lies in the same plane as the flexor digitorum profundus.

Origin and insertion

It arises from the grooved anterior surface of the body of the radius, extending from immediately below the tuberosity and oblique line to within a short distance of the pronator quadratus muscle.

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, or from the medial epicondyle of the humerus.

The fibers end in a flattened tendon, which passes beneath the flexor retinaculum of the hand through the carpal tunnel. It is then lodged between the lateral head of the flexor pollicis brevis and the oblique part of the adductor pollicis, and, entering an osseoaponeurotic canal similar to those for the flexor tendons of the fingers, is inserted into the base of the distal phalanx of the thumb.


The anterior interosseous nerve (a branch of the median nerve) and the anterior interosseous artery and vein pass downward on the front of the interosseous membrane between the flexor pollicis longus and flexor digitorum profundus. Injuries to tendons are particularly difficult to recover from due to the limited blood supply they receive.


The flexor pollicis longus is a flexor of the phalanges of the thumb; when the thumb is fixed, it assists in flexing the wrist.


Slips may connect with flexor digitorum superficialis, flexor digitorum profundus, or the pronator teres. An additional tendon to the index finger is sometimes found.

Additional images

External links

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated. Please edit the article if this is the case, and feel free to remove this notice when it is no longer relevant.

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