Flexor digitorum profundus m

The FDP is the deeper of the digital flexors.  It originates from the ulna and interosseous membrane, its 4 tendons pass through the carpal tunnel, and they insert into the distal phalanges of digits 2-5.  The radial half of the muscle is innervated by the median n., and the ulnar half by the ulnar n.  Because the muscle tendons cross the wrist, MCP, and both the proximal and distal IP joints, it flexes all those joints.