The belly of the |flexor digitorum profundus| lies on the forearm. It originates from the inner side of the |ulna|, extends down the forearms and divides into four ~tendons~. These ~tendons~ insert in the base of the last (distal) |phalanges| of the four fingers. A ~tendon~ does not insert in the thumb. This muscle is used to flex (bend) the fingers, but can do so only after the |flexor digitorum superficialis| has contracted. The muscle also assists in flexing the wrist.
