Which muscle closes the thumb against the palm?

• A. Popliteus
• B. Sciatic nerve
• C. Opponens pollicis
• D. Anterior scrotal arteries

Answer: (C)

The movement of closing the thumb against the palm is called opposition, which brings the thumb across the palm to touch the other digits. The muscle primarily responsible for this action is the opponens pollicis, a key muscle of the thenar eminence. It originates around the carpal bones and flexor retinaculum and inserts on the first metacarpal, enabling flexion and medial rotation of the thumb so its pad meets the pads of the other fingers. This coordinated action allows a precise pinch and grasp. The other options don’t relate to thumb movement: the popliteus is a knee muscle, the sciatic nerve is a major nerve, and the anterior scrotal arteries are blood vessels.