Which muscle pronates the forearm, originating from the medial condyle of the humerus and the coronoid process of the ulna?

• A. Palmaris Longus
• B. Flexor Carpi Radialis
• C. Pronator Teres
• D. Teres Major

Answer: (C)

Pronation of the forearm is produced by muscles that cross the radioulnar joints, with one two-headed muscle specifically designed to pull the radius over the ulna. This muscle originates from the medial condyle of the humerus and the coronoid process of the ulna, and it inserts on the lateral surface of the radius. When it contracts, it rotates the radius around the ulna, turning the palm downward. It also helps flex the elbow when the forearm is pronated. The other muscles listed don’t perform this action: one is primarily a wrist flexor, another flexes and abducts the wrist, and the last is a shoulder muscle involved in arm movements rather than forearm pronation.