The pronator quadratus is a quadrilateral-shaped, flat, and short deep muscle of the forearm located in the anterior compartment. It lies in the distal part of the forearm and is the deepest of the anterior forearm muscles.

This muscle overlies the distal one-quarter of the radius, ulna, and interosseous membrane, and functions as a pronator muscle. It lies deep to the tendons of the flexor pollicis longus, flexor digitorum profundus, and flexor digitorum superficialis muscles. Additionally, its mean length has been reported as approximately 2.36 inches (6 centimeters), while its width averages around 1.38 inches (3.5 centimeters).

Origin: distal one-quarter of the anteromedial aspect of the ulna.

Insertion: distal one-quarter of the anterolateral aspect of the radius.

Action: pronation of the forearm at the distal radioulnar joint; stabilization of the distal radioulnar joint.

Innervation: anterior interosseous nerve (C7 - C8), a branch of the median nerve.

Blood supply: anterior interosseous artery, which is a branch of the common interosseous artery (it originates from the ulnar artery).

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Anterior compartment of forearm muscles: fourth layer