MUSCLES OF THE PELVIC LIMBS. 205 
is called extension in the foot is analogous to what is called 
flexion in the hand, so that the extensors of the foot are most 
readily to be compared with the flexors of the hand.) 
M. plantaris (Fig. 90, 7; Fig. 91, 7).—A fusiform muscle 
covered distally by the gastrocnemius, but appearing between 
the two heads of the gastrocnemius at their proximal ends 
(Fig. go, 7). 
Origin by a strong tendon from the middle of the lateral 
border of the patella and by fleshy fibres from the ventral 
border of the lateral sesamoid. 
The patellar tendon ends in a flattened head which passes 
ventrad over the lateral epicondyle of the femur and then 
curves distad; it is closely united with the lateral head of the 
gastrocnemius. The muscle ends in a thick tendon which 
passes through a sheath formed by the tendons of the gastroc- 
nemius and soleus, and the fascia of the shank. The tendon 
passes over the grooved proximal end of the calcaneus onto its 
ventral surface. It is held in place against the groove by two 
sheets of aponeurosis, which leave the tendon on either side for 
a distance of more than.a centimeter and are attached to the 
lateral surfaces of the calcaneus at its proximal end. Lateral 
motion is thus hindered, while longitudinal motion is permitted. 
Between this tendon and the tendon of Achilles is a synovial 
bursa which aids the gliding movement of the tendon. In the 
sole of the foot opposite the distal end of the calcaneus the 
tendon broadens and ends in the flexor brevis digitorum (pedis 
perforatus) muscle, which might also be considered as a second 
part of the plantaris. In man the plantaris is inserted into the 
calcaneus along with the gastrocnemius. 
Relations.—The muscle is covered throughout by the two 
heads of the gastrocnemius (Fig. 90, #; Fig. 91, £), except 
at, the proximal end (Fig. go, 2), where it is in contact with the 
integument. Inner surface in relation with the popliteus (Fig. 
92, #), the soleus (Fig. 90, 9), the flexor longus digitorum 
(Fig. 91, 2), and flexor longus hallucis (Fig. 91, 7). 
M. soleus (Fig. 90, 0).—A flat fusiform muscle lying 
beneath the plantaris. 
Origin by muscle-fibres from the lateral surface of the head 
