[2] A ventral forearm muscle, the flexor pollicis longus originates on the anterior side of the radius distal to the radial tuberosity and from the interosseous membrane.

It passes through the carpal tunnel in a separate tendon sheath, after which it lies between the heads of the flexor pollicis brevis.

It is innervated by the anterior interosseus branch of the median nerve (C7-C8)[3] Three dorsal forearm muscles act on the thumb: The abductor pollicis longus originates on the dorsal sides of both the ulna and the radius, and from the interosseous membrane.

[4] The extensor pollicis longus originates on the dorsal side of the ulna and the interosseous membrane.

Passing through the third tendon compartment, it is inserted onto the base of the distal phalanx of the thumb.

It uses the dorsal tubercle on the lower extremity of the radius as a fulcrum to extend the thumb and also dorsiflexes and abducts the hand at the wrist.

Passing through the first tendon compartment together with the abductor pollicis longus, it is attached to the base of the proximal phalanx of the thumb.

[4] The tendons of the extensor pollicis longus and extensor pollicis brevis form what is known as the anatomical snuff box (an indentation on the lateral aspect of the thumb at its base) The radial artery can be palpated anteriorly at the wrist(not in the snuffbox).

The thenar eminence refers to the group of muscles on the palm at the base of the thumb.

The flexor pollicis brevis, which lies next to the abductor, will flex the thumb, curling it up in the palm.

[6] The first dorsal interosseous, one of the central muscles of the hand, extends from the base of the thumb metacarpal to the radial side of the proximal phalanx of the index finger.