The pronator quadratus muscle is thin and quadrangular, lying deep on the distal end of forearm. It is formed by transverse muscle fibers that stretch directly over the interosseous membrane. It arises from the distal end of palmar surface of ulna. Then it extends over sideways and laterally to be inserted into the palmar surface of radius on the same level. It is a fourth-layer muscle, which is partially covered by the tendons of the flexor digitorum superficialis and profundus as well as by the flexor pollicis longus muscle.
Action/Function
When contracted, the pronator quadratus pronates the distal end of forearm as it twists the hand around so that the palm faces downwards.
Innervation
This powerful square muscle is innervated by the median nerve (C6-C8).
Blood Supply
The pronator quadratus muscle is supplied by the anterior interosseous artery.
Below, the fourth-layer muscles of forearm, which rotate the forearm: pronator teres, supinator and pronator quadratus.
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