The muscles of thenar eminence are a group of four short muscles located on the lateral aspect of palm of human hand, at the base of the thumb (radial side of palm). They are four in number and they are innervated by the median (C6-C7) and ulnar (C8-T1) nerve. Their source of blood supply are the palmar branch of radial artery. Remember: the muscles of thumb are eight in number as four of them are located in forearm, while the other four lies at the base of thumb (thenar) but all of them move the short digit of hand.
1) Oppenens pollicis muscle.- Triangular in shape, it arises from the crest of the trapezium bone and the flexor retinaculum, and it is inserted into the first metacarpal bone. Action: it opposes the thumb in relation to the fingers, especially the little and ring finger.
2) Flexor pollicis brevis.- It is a superficial muscle which lies medially beside the abductor pollicis brevis. It arises from the flexor retinaculum, the trapezium and trapezoid bones. It is inserted into the base of proximal phalanx of thumb. Action: it flexes the proximal phalanx of thumb.
3) Adductor pollicis muscle.- Lying deep in the palm of hand, it emerges from the radiate carpal ligament, the capitate bone, and the third metacarpal bone. It is inserted into the base of proximal phalanx of thumb. Action: it adducts the thumb (it pulls it medially), assisting in flexing the proximal phalanx.
4) Abductor pollicis brevis.- It lies superficially, arising from the tendon of the abductor pollicis longus muscle and tubercle of trapezium. It is inserted into the lateral side of proximal phalanx of thumb. Action: it abducts thumb (it draws it away from the medial plane) and holds it in mild position.
Below, view of palm of right hand, showing the muscles of thenar eminence. Notice that the abductor pollicis muscle was cut off to expose the opponens pollicis.
