206 THE MUSCLES. 
of the fibula, and by tendon-fibres from the proximal two-fifths 
of its ventral border. 
Insertion.—The muscle ends in a slender tendon which 
joins the lateral border of the gastrocnemius tendon to form the 
tendon of Achilles (Fig. 90, 2), which forms the sheath of the 
plantaris tendon. 
Relations.-Outer surface with the gastrocnemius (Fig. go, 
m) and plantaris (Fig. 90, 7). Inner surface with the peroneus 
longus (Fig. 90, g), peroneus tertius (Fig. 90, v), and flexor 
hallucis (Fig. 91, 72). 
Action.—Assists the gastrocnemius to extend the foot. 
M. triceps sure.—The gastrocnemius and the soleus are 
sometimes considered as forming a single muscle, with three 
heads, under the name triceps sure. 
M. popliteus (Fig. 92, #).—A triangular muscle passing 
from the femur obliquely toward the medial side over the ven- 
tral surface of the proximal end of the tibia. 
Origin by a strong tendon from the popliteal groove on the 
surface of the lateral epicondyle of the femur. In the tendon 
is a sesamoid bone, the popliteal bone (Fig. 61, 5, page 89), 
which glides over the ventral part of the lateral articular facet 
on the proximal end of the tibia. As the muscle passes over 
the joint it is closely attached to the joint capsule. From the 
popliteal bone, which with the tendon lies within the capsule 
of the knee-joint, the muscle-fibres diverge to their 
Insertion into the proximal end of the ventral surface of the 
tibial shaft on the medial side of the medial oblique ridge. 
The area of insertion extends slightly onto the medial surface 
of the bone. 
Relations.—-Outer surface with the gastrocnemius (Fig. 
92,7) and plantaris (Fig. 91, 7), and with the tendon of the 
semitendinosus (Fig. 92, 7). Distal border with the origins 
of the soleus and flexor longus digitorum. Inner surface with 
the capsule of the knee-joint and the tibia. 
Action.—Rotates the thigh so as to turn the toes inward. 
The three following deep muscles on the ventral surface of 
the shank are covered by a deep fascia (the deep crural fascia) 
