The flexores digitorum profundi lies on the caudal surface of tibia covered by the gastrocnemius and the superficial digital flexor.
It is divided in lateral digital flexor (formerly flexor hallucis longus) and medial digital flexor (formerly flexor digitorum longus). The tendons of these two muscles unite to deep flexor tendon that the divides to terminate on flexor surface of each distal pahlanx.
Lateral digital flexor
Origin: Caudal surface of the proximal three-fifths of the fibula and the proximal caudolateral border of the tibia and the interosseus membrane.
Insertion: Via the deep flexor tendon to the hallucis.
Action: Flexion of the hallucis.
Medial digital flexor
Origin: Head of the fibula, the popliteal line and the fascial leaf separating it from the flexor hallucis longus.
Insertion: Bases of the distal phalanges.
Action: Flexion of the digits.