quality:corruption, structural:reformatting
Thenar eminence

The flexor pollicis brevis is a two-headed muscle. The superficial head arises on the flexor retinaculum, while the deep head originates on three carpal bones: the trapezium, trapezoid, and capitate. The muscle is inserted onto the radial sesamoid bone of the metacarpophalangeal joint. It acts to flex, adduct, and abduct the thumb, and is therefore also able to oppose the thumb. The superficial head is innervated by the median nerve, while the deep head is innervated by the ulnar nerve (C8-T1). Due to a common interconnection between the median and ulnar nerves in the hand (Riche-Cannieu interconnection), the median nerve may innervate the flexor pollicis brevis in 35% of people. It is innervated by the ulnar nerve in 50% of people and by both the median and ulnar nerves in 15%.