THE LOWER LIMB 519 



rated superficially by a longitudinal groove, and when the lips of 

 this groove are held apart a tendinous band or raphe is seen to he 

 between them. The fleshy fasciculi of both heads are short and 

 oblique, and they terminate upon the lower tendon, which extends 

 upwards upon the deep or anterior surface of the muscle in the form 

 of an expanded aponeiuosis. The shortness of the fleshy bundles 

 gives the muscle great power of action, but the range of movement 

 is limited. 



The internal head is separated from the tendon' of the semimem- 

 branosus by a large bursa, called the popliteal bursa, which fre- 

 quently (one in five) communicates with the synovial membrane 

 of the knee-joint. Another small bursa is situated a little higher, 

 between the internal head and the posterior surface of the femur. 

 In the external head a sesamoid fibro-cartilage is occasionally met 

 with. 



Soleus. — ^This flat muscle has been so named from its resemblance 

 to a sole-fish. 



Origin. — (i) The posterior surface of the head, and the upper 

 third of the posterior surface of the shaft, of the fibula ; (2) the 

 postero-external intermuscular septum ; (3) the fibrous arch 

 thrown over the popliteal vessels and internal popliteal nerve ; 

 (4) the oblique or popliteal line of the tibia ; and (5) the internal 

 border of the tibia over its middle third. 



Insertion.^-The tendon joins that of the gastrocnemius at the 

 centre of the leg to form the tendo Achillis, which is inserted into 

 the middle zone on the posterior surface of the tuber calcis. 



Nerve-supply. — (i) The internal popliteal nerve, the branch from 

 which enters the muscle on its superficial or posterior surface near 

 the upper border ; and (2) the posterior tibial nerve, the branch 

 from which enters the muscle on its deep or anterior surface near 

 the centre of the leg. 



Action. — Acting from its origin the muscle is a powerful extensor 

 of the foot upon the leg, thus raising the heel. Acting from its 

 insertion, as when the ankle-joint is fixed by the muscles of the 

 anterior aspect of the leg, the soleus steadies the leg upon the foot. 



The fasciculi of this muscle are short and oblique, like those of 



the gastrocnemius. It has therefore great power of action, but its 



range of movement is limited. Only a hmited number of the 



fibres of the soleus spring directly from the bony surfaces. The 



majority arise from two aponeurotic laminae, which are almost 



entirely concealed within the muscle, and which descend, one from 



the fibula, and the other from the oblique line of the tibia and the 



fibrous arch over the popliteal vessels. The fibres which arise 



from the anterior surfaces of these two laminae terminate upon a 



[ median tendinous band or raphe, which is deeply placed, and those 



i arising from their posterior surfaces end upon a broad expanded 



aponeurosis, which covers the superficial or posterior surface of 



1 the muscle, giving it an appearance similar to that of the deep 



or anterior surface of the gastrocnemius. This aponeurosis is 



