Final answer:
The flexor pollicis longus is a muscle located in the deep posterior compartment of the forearm. It flexes the thumb at the interphalangeal joint and the metacarpophalangeal joint. It is innervated by the anterior interosseous nerve and supplied by the radial and ulnar arteries.
Step-by-step explanation:
The flexor pollicis longus is a muscle located in the deep posterior compartment of the forearm. Its insertion point is on the base of the distal phalanx of the thumb. The action of the flexor pollicis longus is to flex the thumb at the interphalangeal joint and the metacarpophalangeal joint. It is innervated by the anterior interosseous nerve, which arises from the median nerve. The blood supply to the flexor pollicis longus comes from the radial and ulnar arteries.