The Extensor Pollicis Longus is a muscle located in the forearm. It is part of the posterior compartment and is responsible for extending the thumb at the metacarpophalangeal and interphalangeal joints. This muscle originates from the ulna and the interosseous membrane, and it inserts into the base of the distal phalanx of the thumb. This muscle plays a crucial role in thumb movements, allowing for actions such as grasping and pinching. It works in coordination with other muscles, including the Extensor Pollicis Brevis and the Abductor Pollicis Longus, to facilitate thumb extension and abduction.