Flexor pollicis longus muscle
muscle of the upper limb
The flexor pollicis longus (; FPL, Latin flexor, bender; pollicis, of the thumb; longus, long) is a muscle in the forearm and hand that flexes the thumb. It lies in the same plane as the flexor digitorum profundus. This muscle is unique to humans, being either rudimentary or absent in other primates. A meta-analysis indicated accessory flexor pollicis longus is present in around 48% of the population.
Human anatomy
Origin and insertion
It arises from the grooved anterior (side of palm) surface of the body of the radius, extending from immediately below the radial tuberosity and oblique line to within a short distance of the pronator quadratus muscle. An occasionally present accessory long head of the flexor pollicis longus muscle is called 'Gantzer's muscle'. It may cause compression of the anterior interosseous nerve.
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. In 40 percent of cases, it is also inserted from the medial epicondyle of the humerus, and in those cases a tendinous connection with the humeral head of the flexor digitorum superficialis is present.
The fibers end in a flattened tendon, which passes beneath the flexor retinaculum of the hand through the carpal tunnel.
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