Flexor pollicis brevis is a short, thick muscle of the thumb. It is composed of two heads, with the superficial head lying directly under the skin, between the opponens pollicis and the adductor pollicis brevis muscle. The deep head is hidden from sight as it is located beneath the superficial portion and the adductor pollicis. Pollicis is the Latin word for thumb; and brevis means short.
The flexor pollicis brevis arises from the flexor retinaculum (a fibrous band forming the carpal tunnel), the trapezium, trapezoid, the capitate bones of carpus, and the base of the first metacarpal bone. The superficial fibers are inserted into the radial sesamoid bone, while the deep portion is inserted into both sesamoid bones of the metacarpophalangeal joint.
Action
The flexor pollicis brevis flexes the proximal phalanx of the thumb. It assists the flexor pollicis longus in closing it when we want to grasp something in the hand.
Innervation
It is supplied by nerve fibers originating from the median nerve (C6-C7), which is part of the brachial plexus.
Blood Supply
This thick muscle of the thumb receives oxygenated blood from the superficial palmar branch of the radial artery, and a branch of the deep palmar arch.
Below, schematic picture of the flexor pollicis brevis (superficial head), lying between the opponens pollicis and the adductor pollicis muscle.
Deep head of flexor pollicis brevis.
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