The flexor pollicis brevis muscle is a muscle in the hand. It flexes the thumb at the first metacarpophalagneal joint. This is in opposition to the extensor pollicis brevis muscle, which extends the thumb. Severe injury to this muscle would impair the thumb's ability to move. The thumb is the most versatile digit of the hand. If the muscles of the thumb are impaired, many actions involving the hand become difficult or impossible. The flexor pollicis brevis originates at the flexor retinaculum of the hand. This refers to a band of fibers that stretch over the hand's carpus. The muscle also possesses an origination point at the trapezium carpal bone. It inserts into the thumb's proximal phalanx bone. With a continuous supply of oxygenated blood, the superficial palmar arch services the muscle. In addition, the superficial palmar venous arch assists in draining deoxygenated blood away. The flexor pollicis brevis muscle is innervated by both the recurrent branch of the median nerve and the deep branch of the ulnar nerve.