innerbody
Diagram

Flexor Pollicis Brevis Muscle

The flexor pollicis brevis muscle is a short muscle that runs from the wrist to the proximal phalanx of the thumb to bend the thumb toward the palm. A flexor muscle is one that decreases the angle between two bones, as in bending the arm at the elbow; raising the leg toward the stomach as in kicking a football; or bringing the lower leg up toward the thigh.