The flexor digitorum profundus helps flex the fingers. The muscle originates in the upper part of the ulna bone. It inserts at the distal phalanges in the tips of the fingers. The muscle’s belly is located in the forearm. However, it is considered a hand muscle because it is primarily used for hand functionality. The muscle's long tendons extend over the wrist and the metacarpals of the hand. Along with the flexor pollicis longus and the pronator quadratus, the muscle helps fill out the forearm. For oxygenated blood, the flexor digitorum profundus muscle relies on the anterior interosseous artery. The muscle is innervated by the anterior interosseous and the ulnar nerves. If either the nerves or the muscle itself suffers injury, the fingers would lose their dexterity.