The flexor pollicis longus is one of several muscles of the human thumb. It is located on the lateral border of anterior side of forearm. It is long and unipennate (having a feather-like form on one side).
This the flexor pollicis longus arises from the upper two-third of the anterior surface of radius and interosseous membrane as well as from the medial epicondyle of humerus. Then it runs down the forearm, parallel to the flexor digitorum profundus, as it becomes a long tendon which travels through the carpal tunnel. Next it is invested by the synovial sheath of the flexor pollicis longus tendon to finally be inserted into the base of the distal phalanx of thumb.
Action
Upon contraction, this long muscle of forearm flexes the distal phalanx of thumb, pulling it towards the palm of hand.
Innervation
The flexor pollicis longus is innervated by the median nerve (C6-C8).
Blood Supply
It receives oxygen-rich blood from muscular branches of the radial, ulnar and anterior interosseous artery.
Below, picture of third-layer muscles of forearm: flexor pollicis longus and flexor digitorum profundus muscle
