5i8 A MANUAL OF ANATOMY 



External or Short Saphenous Nerve. — This nerve is formed by 

 the union of the ramus communicans tibiahs of the internal pop- 

 Hteal and the ramus communicans fibularis of the external pop- 

 liteal. The union takes place at, or just below, the centre of the 

 calf, and superficial to the deep fascia. The nerve descends on the 

 outer side of the short saphenous vein, and external to the tendo 

 AchilHs. It then passes behind and below the external malleolus, 

 and so reaches the outer border of the foot, along which it passes 

 to the outer side of the little toe, of which it is the dorsal digital 

 nerve. The nerve supplies the integument of the back of the leg 

 in its lower half, the external malleolar region, the outer side of 

 the calcaneum, and the outer border of the foot and outer side of 

 the little toe. It also furnishes articular branches to the ankle- 

 joint, and the astragalo-calcaneal articulation. 



Muscles. — The muscles of the back of the leg are divided into two 

 groups — superficial and deep. 



Superficial Group. — This group comprises the gastrocnemius, 

 soleus, and plantaris, which are collectively called the sural (calf) 

 muscles. 



Gastrocnemius. — This muscle is so named because it forms the 

 ' belly of the leg,' that is to say, the fleshy enlargement at the 

 back of the leg which is called the calf. 



Origin. — ^The external head arises from (i) the outer surface of the 

 external condyle of the femur immediately above the commence- 

 ment of the popliteal groove, and close behind and above the 

 external tuberosity ; and (2) the adjacent part of the posterior 

 surface of the femur, vertically, for at least an inch immediately 

 external to the lower part of the external supracondylar ridge. 

 The internal head arises from (i) an oblique impression on the 

 posterior surface of the femur immediately above the internal 

 condyle, and extending inwards for fully an inch as far as the 

 adductor tubercle ; and (2) the lower extremity of the internal 

 supracondylar ridge for a short distance. 



Insertion.— The fleshy part of the muscle gives place to a flat 

 tendon, which joins the subjacent tendon of the soleus at the 

 centre of th» leg to form the tendo Achillis. Through this latter 

 the gastrocnemius is inserted into the middle zone on the posterior 

 surface of the tuber calcis, a bursa intervening between the tendon 

 and the upper zone. 



Nerve-supply. — ^The internal popliteal nerve, which furnishes two 

 branches, one for each head. 



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 gastrocnemius is a flexor of the 

 knee-joint, flexing the femur upon the tibia. 



The two heads come into contact at the junction of the upper 

 sixth and lower five-sixths of the leg, and so they limit the lower 

 part of the popliteal space. After coming together they are sepa- 



