620 A MANUAL OF ANATOMY. 



and the trunk becomes the external saphenous. (3) The 

 muscular branches. These supply the gastrocnemius, plan- 

 taris, popliteus, and soleus, muscles. 



Gastrocnemius. Figs. 128, 129, 131. 



Origin. By two heads from the posterior surface of the 

 femur above each condyle and from the condyloid ridges 

 of the same. 



Insertion. By the tendo-Achillis, common to it and the 

 soleus, into the lower part of the posterior surface of the 

 os calcis. 



A bursa is found under the inner head of the muscle 

 and another between the tendo-Achillis and the upper part 

 of the os calcis. 



Nerve Supply. The internal popliteal. 



Action. To flex the leg upon the thigh, to extend the 

 foot upon the ankle. 



In the first case the muscle acts with the flexors of the 

 knee, and in the second with the extensors of the foot and 

 ankle. 



The Popliteal Space. Fig. 128. 



This is the hollow behind the knee joint. It is diamond- 

 shaped. 



Its boundaries are formed as follows : 



Above, the biceps externally, the semitendinosus, semi- 

 membranosus, the gracilis, and the sartorius, internally. 

 Below, by the diverging heads of the gastrocnemius and in 

 addition the plantaris at the outer side. On either side of 

 the middle of the space are the condyles of the femur. 



The "floor" of this space is formed by the back of the 

 lower end of the femur, the posterior ligament of the knee 

 joint, the posterior part of the articular rim of the tibia 

 (covered by the above ligament) and the popliteus muscle 





