The flexor pollicis brevis is a small muscle located in the hand. It is responsible for flexing the thumb at the metacarpophalangeal joint, allowing for movements such as gripping and pinching. This muscle is part of the thenar eminence, which is the fleshy mass at the base of the thumb. The flexor pollicis brevis has two heads: the superficial head and the deep head. It is innervated by the median nerve and plays a crucial role in hand function. Proper functioning of this muscle is essential for tasks that require thumb dexterity and strength.