GASTROCNEMIUS 369 



From the inner extremity of this loop, two l)ands of fil)res of varying distinctness 

 proceed: one passes upwards and inwards to join the front border of the internal 

 malleolus; the other, which is usually the weaker, more directly inwards over the 

 scaphoid l)one to join the inner border of the plantar fascia. Beneath this inner por- 

 tion of the lower part of the anterior annular ligament the tendons of the extensor 

 proprius hallucis and til)ialis anticus are contained in sejjarate synovial sheaths. 



The external annular ligament passes from the posterior border of the external 

 malleolus to the outer border of the tuberosity of the calcaneum and to the posterior 

 part of the junction of the lower and outer surfaces of the calcaneum. It is con- 

 tinuous aV)ove with the deep fascia covering the calf muscles and the peronei; and 

 also with the sheet of fascia which separates the two superficial from the two deeper 

 layers of nuiscles at the back of the leg. Its deep surface is attached to the pero- 

 neal tubercle on the outer side of the calcaneum. 



The internal annular ligament extends from the posterior border of the 

 internal malleolus to the inner border of the tuberosity of the calcaneum. It is 

 also continuous above with the deep fascia of the leg and with the sheet of fascia 

 which intervenes between the soleus and the deeper layers of muscle at the back of 

 the leg. 



MUSCLES OF THE BACK OF THE LEG 



The muscles in this region are arranged in two layers above, in four below, 

 The first layer consists of the gastrocnemius and plantaris. 



First Layer 



1. GASTROCNEMIUS 



The gastrocnemius — named from ya<jrr,p = the belly, and x^rj/irj = the calf, 

 because it forms the enlargement of that part of the leg — is dou)>le-headed, each 

 head consisting of a fusiform mviscle, the lower part of which blends with its fellow 

 so as to form a common tendon of insertion. These two heads constitute the 

 femoral origin of the great triceps sura? muscle. 



Origin. — Outer head : a Avell-markecl impression upon the upper and posterior 

 part of the outer surface of the external condyle and the adjacent part of the 

 })Osterior surface of the fenmr just above the external condyle. 



Inner head : an oval impression placed transversely across the posterior surface 

 of the femur above the internal condyle, and reaching inwards to the back of the 

 adductor tul)ercle. 



Insertion. — By the tendo Achillis (so named from the legend that the heel, 

 into which this tendon is inserted, was the only vulnerable part of the hero 

 Achilles) into the middle area on the posterior surface of the calcaneum. 



Structure. — The two heads arise by short strong tendons; that of the inner 

 is the stronger and thicker. These tendons converge downwards, and are suc- 

 cei'ded l)y large fleshy expansions which unite at the ui)per p)art of the middle 

 third of the leg. Near this })oint the tendon of insertion begins as an internuis- 

 cular septum between the two bellies of the muscle. This becomes thicker and 

 stronger, and expands into a ]>road aponeurosis which covers the anterior surface of 

 the united muscle. Just below the middle of the leg the fleshy fibres temiinate 

 upon the back of this aponeurosis in two curves the convexity of which is down- 

 wards, that of the inner portion of the nuiscle descending about half an inch 

 (1"2 cm.) lower than the outer. The strong aj)oneurosis becomes narrower and at 

 the same time thicker, and after receiving the fibres of the soleus muscle is known 

 by the name of the tendo Achillis. 

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