As its name suggests, it opposes the thumb, bringing it against the fingers. The opponens pollicis lies deep to abductor pollicis brevis. The flexor pollicis brevis, which lies next to the abductor, will flex the thumb, curling it up in the palm. The abductor brings the thumb away from the other four fingers. The most superficial muscle in the thenar group is the abductor pollicis brevis. The tendons of the extensor pollicis longus and extensor pollicis brevis form what is known as the anatomical snuff box (an indentation on the lateral aspect of the thumb at its base) The radial artery can be palpated anteriorly at the wrist(not in the snuffbox). It is innervated by the deep branch of the radial nerve ( C8- T1). It extends the thumb and, because of its close relationship to the long abductor, also abducts the thumb. Passing through the first tendon compartment together with the abductor pollicis longus, it is attached to the base of the proximal phalanx of the thumb. The extensor pollicis brevis originates on the ulna distal to the abductor pollicis longus, from the interosseus membrane, and from the dorsal side of the radius.
It is innervated by the deep branch of the radial nerve (C7-C8). It uses the dorsal tubercle on the lower extremity of the radius as a fulcrum to extend the thumb and also dorsiflexes and abducts the hand at the wrist. Passing through the third tendon compartment, it is inserted onto the base of the distal phalanx of the thumb. The extensor pollicis longus originates on the dorsal side of the ulna and the interosseous membrane. Except for abducting the hand, it flexes the hand towards the palm and abducts it radially. A part of the tendon reaches the trapezium, while another fuses with the tendons of the extensor pollicis brevis and the abductor pollicis brevis. Passing through the first tendon compartment, it inserts to the base of the first metacarpal bone. The abductor pollicis longus originates on the dorsal sides of both the ulna and the radius, and from the interosseous membrane. Three dorsal forearm muscles act on the thumb: It is innervated by the anterior interosseus branch of the median nerve ( C7- C8) It finally attaches onto the base of the distal phalanx of the thumb. It passes through the carpal tunnel in a separate tendon sheath, after which it lies between the heads of the flexor pollicis brevis. Flexor pollicis longus (left) and deep muscles of dorsal forearm (right)Ī ventral forearm muscle, the flexor pollicis longus originates on the anterior side of the radius distal to the radial tuberosity and from the interosseous membrane.
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