220 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 303. — The superficial muscles of the calf of the leg. 



Fig. 304.— The second layer of the calf muscles. The gastrocnemius has been removed. 

 Yi G . 305.— The deep musculature of the calf, seen from behind and from the inner side. 



The triceps surse has been removed. 



which is situated upon the posterior aspect of the knee and leg; its muscular belly is situated 

 chiefly in the sural region, while its tendinous portion is located in the posterior crural region. 

 The two heads, the inner head (gastrocnemius medialis) and the outer head (gastrocnemius later- 

 alis), arise by tendons from the upper extremities of the epicondyles of the femur and exhibit 

 aponeuroses upon their internal and external surfaces, extending downward almost to the middle 

 of the muscle. Beneath the somewhat stronger inner head is situated a bursa which communi- 

 cates with the interior of the knee-joint, the inner gastrocnemial bursa (Fig. 304) (see also page 

 136). Both heads of the muscle pass immediately over the posterior surface of the knee-joint 

 forming the inferior boundary of the popliteal fossa, and below the articulation they become 

 broader and are united in such a manner that their line of union is indicated by a median groove 

 which extends almost to their insertion into the common tendon. Somewhat below the middle 

 of the leg, the muscular tissue terminates rather suddenly in a broad tendon which becomes nar- 

 rower and fuses with that of the soleus. 



The soleus (Fig. 304) is a flat, very broad, and rather thick muscle, the upper portion of 

 which is covered by the gastrocnemius, the lower portion being situated immediately beneath the 

 " deep fascia to either side of the gastrocnemius tendon. The muscle arises from the capitulum, 

 posterior surface, and outer border of the fibula, from the popliteal line and the surface immedi- 

 ately below it upon the posterior surface of the tibia, and from a tendinous arch passing over the 

 popliteal vessels between the tibia and fibula, the tendinous arch 0} the soleus. Shortly after its 

 origin the muscle becomes broader, and exhibits upon its posterior aspect an aponeurosis which 

 is continuous with a tendon which fuses with that of the gastrocnemius and also receives the 

 insertions of lower lying lateral muscular fasciculi. This tendon of the triceps suras, broad at first 

 and becoming narrower and thicker as it passes downward, is known as the calcaneal tendon (tendo 

 Achillis). It is the strongest tendon in the entire body and is inserted into the upper margin 

 of the tuberosity of the calcaneus. 



The triceps suras also includes the plantaris (Fig. 304), a small muscle with a very short but 

 rather strong belly and a very long slender tendon. It arises from the external epicondyle of the 

 femur, to the inner side of and somewhat above the outer head of the gastrocnemius, which partly 

 covers it, and the short muscular belly is directed obliquely outward and downward between the 

 gastrocnemius and soleus. The slender tendon lies upon the inner side of the soleus, runs down- 

 ward along the inner margin of the tendo Achillis, and fades away partly into this structure and 

 partly into the deep fascia of the leg. 



The triceps sura: is supplied by the tibial nerve. It produces plantar flexion of the foot. The plantaris acts as a 

 tensor of the tendo Achillis. 



THE POPLITEUS. 



The popliteus (Figs. 304 and 305) is a flat triangular muscle which is in a class by itself. It 

 is situated in the same layer as the soleus, with which it is directly related by its lower and outer 



