The most superficial muscle in the thenar group is the abductor pollicis brevis. The abductor brings the thumb away from the other four fingers. The flexor pollicis brevis, which lies next to the abductor, will flex the thumb, curling it up in the palm. The opponens pollicis lies deep to abductor pollicis brevis. As its name suggests it opposes the thumb, bringing it against the fingers. This is a very important movement, as most of human hand dexterity including grip comes from this action.
when opposing the thumb which muscle is active
opponens pollicis