These are four in number, and they form a fleshy mass at the radial border the palm, covered by the thenar portion of the palmar fascia, and called the thenar eminence or ball of the thumb. They are the abductor pollicis, the opponens pollicis, the flexor brevis pollicis, and the adductor pollicis.
The flexor brevis pollicis (French: muscle court fléchisseur du pouce) - named from its action and short length in compari- son with the long flexor - consists of two heads : each forming a flat triangular sheet.
The opponens pollicis, or flexor ossis metacarpi pollicis, is named from its action, as it helps in opposing the thumb to the other fingers and at the same time is a flexor of the first metacarpal bone. It is a short, thick, triangular sheet.
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