The flexor pollicis longus is one of three muscles in the deep compartment of the anterior muscles of the forearm.

The two other muscles are the flexor digitorum profundus and the pronator quadratus.

The name in Latin translates as the long flexor of the thumb. The muscle is unique to humans, and is either a non-functional or not present in other primates.

Origin
  • Middle half of the anterior surface of the radius
  • Anterior surface of adjacent interosseus membrane
Insertion

Base of the distal phalanx of the thumb

Innervation

Anterior Interosseus Nerve (from median nerve)

Blood Supply

Anterior interosseus artery (ulnar artery -> common interosseus artery -> ant. interosseus artery).

Antagonist
  • Extensor pollicis longus muscle
  • Extensor pollicis brevis muscle
Action
  • Flexes the phalange of the thumb
  • If the thumb is fixed, can assist in flexinfg the wrist