208 THE MUSCLES. 
insertions are identical with those of the flexor profundus digi- 
torum of the hand. 
Relations. —Outer surface with the soleus (Fig. 90, 0) and 
plantaris (Fig. 91, 7). Lateral border with the soleus, the 
peroneus tertius (Fig. 90, ), and peroneus brevis (Fig. go, s). 
Medial border with the tibialis posterior (Fig. 91, 0) and flexor 
longus digitorum (Fig. 91, 2). 
Action.—Flexor of the phalanges. 
(2) M. flexor longus digitorum (Fig. 91, 7). 
Origin by muscle- and tendon-fibres from the ventral sur- 
face 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, 0), 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 ten- 
don 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. 
Relations.—Outer surface with the medial head of the gas- 
trocnemius (Fig. 91, &) and with the superficial fascia. Inner 
surface with the tibialis posterior (Fig. 91, 0). Medial border 
at the proximal end with the popliteus (Fig. 92, £), lateral 
border with the tibialis posterior (Fig. 91, 0), and flexor longus 
hallucis (Fig. 91, #2). 
Action.—F lexor of the phalanges. 
M. tibialis posterior (Fig. 91, 7).—A slender flat fusiform 
muscle beneath the flexor longus digitorum and between it and 
the flexor longus hallucis. 
Origin by fleshy fibres from nearly the whole medial surface 
of the head of the fibula, from the inner surface of the apo- 
neurosis between it and the flexor longus digitorum (x), and by 
a few fleshy fibres from the ventral surface of the tibia between 
the oblique ridges. Some fibres may also arise from the outer 
surface of the aponeurosis covering the flexor longus hallucis 
(m). The muscle ends at about the middle of the tibia in a 
slender flat tendon which passes parallel to the tendon of the 
flexor longus digitorum (#) through the dorsal groove on the 
