The pronator quadratus is one of three muscles in the deep compartment of the anterior muscles of the forearm.
The two other muscles are the flexor digitorum profundus and the flexor pollicis longus.
The pronator quadratus, as the name suggests is a square-shaped and flat muscle which is located in the distal forearm and assists in pronation of the forearm, pulling the distal end of the radius anteriorly over the ulna.
Anterior medial surface of the distal ulna
Anterior lateral surface of the distal radius
Pronator quadratus as the name suggests pronates the forearm by pulling the lateral aspect of the distal radius anteriorly over the ulna.
The pronator teres is sometimes absent but this is not functionally significant due to the other forearm pronator, the pronator teres.
Anterior Interosseus Nerve (from median nerve)
Anterior interosseus artery (ulnar artery → common interosseus artery → ant. interosseus artery).