The opponens pollicis is a small, triangular muscle in the hand, which functions to oppose the thumb.

It passes downward and laterally, and is inserted into the whole length of the metacarpal bone of the thumb on its radial side.

Like the other thenar muscles, the opponens pollicis is innervated by the recurrent branch of the median nerve.

The part of apposition that this muscle is responsible for is the flexion of the thumb's metacarpal at the first carpometacarpal joint.

This article incorporates text in the public domain from page 461 of the 20th edition of Gray's Anatomy (1918)