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The thenar muscles form the muscular eminence at the base of the thumb. These four short muscles surround the metacarpal bone of the thumb and produce a wide range of precise thumb movements. One of the important actions produced by a thenar muscle is opposition of the thumb. The ability to oppose the thumb is an important and unique feature humans share with other primates. The opponens muscle differs from other muscles in the thenar group by not crossing the metacarpophalangeal joint. Like other anterior muscles in the upper limb, these muscles receive innervation via the median and ulnar nerves.