The abductor pollicis longus is a muscle located in the forearm. It plays a crucial role in the movement of the thumb, specifically by allowing it to move away from the hand. This muscle originates from the posterior surfaces of the radius and ulna bones and inserts into the base of the thumb's first metacarpal bone. This muscle is part of the group known as the extrinsic muscles of the hand, which are responsible for hand and finger movements. Proper functioning of the abductor pollicis longus is essential for activities that require thumb opposition and grip, making it important for tasks like holding objects and writing.