 flexor hallucis longus arises on the back of the fibula (i.e.on the lateral side), and its relatively thick muscle belly extends distally down to the flexor retinaculum where it passes over to the medial side to stretch across the sole to the distal phalanx of the first digit.The popliteus is also part of this group, but, with its oblique course across the back of the knee, does not act on the foot.