THE POSTERIOR TIBIO-FIBULAR REGION. 



523 



accessory portions of the muscle derived from the bifurcations of the linea aspera, 



unite at an angle upon a median tendinous 



raphe below : the remaining fibres converge 



to the posterior surface or an aponeurosis 



which covers the anterior surface of the 



muscle, and this, gradually contracting, 



unites with the tendon of the Soleus, and 



forms with it the tendo Achillis. 



Relations. By its superficial surface, 

 with the fascia of the leg, which separates 

 it from the external saphenous vein and 

 nerve ; by its deep surface, with the posterior 

 ligament of the knee-joint, the Popliteus, 

 Soleus, Plantaris, popliteal vessels, and in- 

 ternal popliteal nerve. The tendon of the 

 inner head corresponds with the back part 

 of the inner condyle, from which it is sepa- 

 rated by a synovial bursa, which, in some 

 cases, communicates with the cavity of the 

 knee-joint. The tendon of the outer head 

 contains a sesamoid fibro-cartilage (rarely 

 osseous) where it plays over the correspond- 

 ing outer condyle ; and one is occasionally 

 found in the tendon of the inner head. 



The Gastrocnemius should be divided across, 

 just below its origin, and turned downward, in order 

 to expose the next muscles. 



The Soleus is a broad flat muscle situated 

 immediately beneath the Gastrocnemius. It 

 has received its name from its resemblance 

 in shape to a sole-fish. It arises by ten- 

 dinous fibres from the back part of the head 

 of the fibula and from the upper third of the 

 posterior surface of its shaft ; from the oblique 

 line of the tibia and from the middle third 

 of its internal border ; some fibres also arise 

 from a tendinous arch placed between the 

 tibial and fibular origins of the muscle, be- 

 neath which the posterior tibial vessels and 

 nerve pass. The fibres pass backward to an 

 aponeurosis which covers the posterior sur- 

 face of the muscle, and this, gradually be- 

 coming thicker and nai'rower, joins with the 

 tendon of the Gastrocnemius, and forms with 

 it the tendo Achillis. 



Relations. By its superficial surface, 

 with the Gastrocnemius and Plantaris ; by 

 its deep surface, with the Flexor longus 

 digitorum. Flexor longus hallucis, Tibialis 

 posticus, and posterior tibial vessels and nerve, from which it is separated by the 

 transverse intermuscular septum or deep transverse fascia of the leg. 



The Tendo Achillis, the common tendon of the Gastrocnemius and Soleus, is 

 the thickest and strongest tendon in the body. It is about six inches in length, 

 and commences about the middle of the leg, but receives fleshy fibres on its 

 anterior surface nearly to its lower end. Gradually becoming contracted below, it 

 is inserted into the lower part of the posterior surface of the os calcis, a synovial 



Tendons of 



PERONEUS LONGUS 



and BREVIS. 



FIG. 331. Muscles of the back of the leg. 

 Superficial layer. 



