(1) =M. flexor longus hallucis= (Fig. 91, _m_).--This lies against the ventral surface of the tibia and fibula beneath the popliteus (Fig. 92, _k_) and soleus (Fig. 90, _o_).
_Origin_ by fleshy fibres, (1) from the sheet of deep crural fascia which dips between it and the tibialis posterior (Fig. 91, _o_) and the flexor longus digitorum (_n_). (2) From the ventral surface of the tibia distad of the lateral oblique line to within one to three centimeters of the distal end of the shaft. (3) From the medial surface of the shaft and head of the fibula and from the whole interosseous ligament. On the fibular side the origin may extend onto the tendon of the popliteus and the fascia of the peroneus longus. The fibres form a flat fusiform mass ending one centimeter from the heel in a strong flat tendon (_m′_) which passes over the groove on the distal surface of the astragalus and over the groove on the sustentaculum tali. The two grooves are converted into a continuous canal by strong transverse ligaments, and the canal is lined by an extension of the synovial bursa of the ankle-joint. Emerging from the canal the tendon broadens and receives on its medial side the insertion of the tendon of the flexor longus digitorum (_n_). The tendon gives origin on its outer surface to the lumbricales and to the common plantar ligament. The tendon continues to broaden until it reaches the middle of the length of the metacarpals; here it divides into four tendons which pass to the terminal phalanges of the digits.
_Insertion._--The relations of the four tendons and their insertions are identical with those of the flexor profundus digitorum of the hand.
_Relations._--Outer surface with the soleus (Fig. 90, _o_) and plantaris (Fig. 91, _l_). Lateral border with the soleus, the peroneus tertius (Fig. 90, _r_), and peroneus brevis (Fig. 90, _s_). Medial border with the tibialis posterior (Fig. 91, _o_) and flexor longus digitorum (Fig. 91, _n_).
(2) =M. flexor longus digitorum= (Fig. 91, _n_).
_Origin_ by muscle- and tendon-fibres from the ventral surface of the tibia over its proximal half between the oblique ridges; by fleshy fibres from an aponeurosis between it and the tibialis posterior (Fig. 91, _o_), and by tendon from the medial surface of the head of the fibula. At the junction of the middle and distal thirds of the bone the muscle ends in a slender tendon which passes through the ventral groove on the medial surface of the tibia and, curving onto the sole of the foot, becomes attached to the medial border of the common tendon described under the last.