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Retract or cut through the flexor digitorum superficialis muscle in the distal third of the forearm just proximal to its tendons. Reflect the belly of the flexor digitorum superficialis muscle proximally to expose the muscles in the deepest layer of the forearm. Identify the flexor digitorum profundus muscle [probe], flexor pollicis longus muscle [two probes], and pronator quadratus muscle.

The flexor digitorum profundus muscle flexes the distal phalanx of the fingers. The flexor pollicis longus muscle flexes the distal phalanx of the thumb. The pronator quadratus muscle, which assists in pronation of the forearm, runs transversely from ulna to radius in the distal forearm.