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Examine the short muscles of the thumb, that form the thenar eminence, or ball of the thumb. It is composed of three muscles, the abductor pollicis brevis muscle, opponens pollicis muscle, and flexor pollicis brevis muscle.Define the borders of the abductor pollicis brevis muscle. It arises from the trapezium and flexor retinaculum and inserts into the lateral side of the proximal phalanx of the thumb. Then, cut it near its insertion and reflect the abductor pollicis brevis muscle proximally.
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