Deep muscles of forearm

The deep muscles of forearm include the flexor digitorum profundus, flexor pollicis longus, and pronator quadratus.

• The flexor digitorum profundus originates from the proximal three-quarters of the anterior and medial surfaces of the ulna and the adjacent interosseous membrane. Its tendons pass through the carpal tunnel to insert onto the distal phalanges of the medial four fingers, allowing for powerful distal interphalangeal joint flexion.

• The flexor pollicis longus arises from the anterior surface of the radius and the adjacent interosseous membrane. Its tendon inserts onto the base of the distal phalanx of the thumb, enabling strong thumb interphalangeal joint flexion.

• The pronator quadratus is a flat, quadrilateral muscle located distally, spanning from the distal ulna to the distal radius. It serves as the primary pronator of the forearm.