FOSSA POPLITEA 237 



nerves. The artery and vein are placed deeply in the 

 space, and in close contact with each other the vein being 

 superficial to the artery throughout. The tibial nerve and 

 the common peroneal nerve lie more superficially. With the 

 exception of the posterior cutaneous nerve of the thigh which 

 descends immediately subjacent to the deep fascia, the tibial 

 nerve is the most superficial structure in the fossa poplitea. 

 It lies superficial to the popliteal vessels, and is readily found 

 by separating the adipose tissue in the middle line of the fossa. 

 The common peroneal nerve will be exposed by dissecting along 

 the proximo-lateral boundary of the space. It lies under 

 shelter of the biceps femoris muscle. Both of these large 

 nerves give off branches, of which the majority are easily 

 secured and readily followed. The articular twigs, however, 

 are very delicate, and great care is required in their 

 dissection. 



In intimate relation to the popliteal artery is the geniculate 

 branch of the obturator nerve. It descends in close apposition 

 with the coats of the artery. As the fat is being cleared out 

 from the fossa the dissector will not fail to observe some 

 small lymph glands in relation to the great vessels. 



Boundaries. The fossa poplitea is diamond - shaped. 

 Above and laterally it is bounded by the biceps femoris muscle; 

 whilst above and medially are the semitendinosus and the semi- 

 membranosus muscles, the former lying upon the posterior surface 

 of the latter. On the medial side of the knee, anterior to the 

 semimembranosus, the gracilis, the sartorius, and the tendon of 

 the adductor magnus, can be exposed. The fossa is bounded, 

 below, by the converging heads of the gastrocnemius. In the 

 formation of the distal and lateral boundary, the lateral head 

 of the gastrocnemius will be seen to be assisted by the small 

 plantaris muscle. 



Dissection. In cleaning the muscles which bound the fossa poplitea 

 there are certain points to be attended to. In the case of the lateral head 

 of the gastrocnemius, care must be taken not to remove the anastomotic 

 nerve, which passes distally and medially upon its surface. In the groove 

 between the heads of this muscle will be seen the medial ctitaneous nerve of 

 the calf. Further, the dissector must not overlook the bursa mucosa 

 which intervenes between the tendon of the semimembranosus and the 

 medial head of the gastrocnemius. This bursa sometimes communicates 

 with a second bursa mucosa, which will be brought into view by lifting the 

 medial head of the gastrocnemius from the medial condyle of the femur. 



The dissection may be carried in an anterior direction on the medial 

 aspect of the limb a little beyond the medial boundary of the fossa, in 

 order to expose the saphenous branch of the arteria genu suprema, the 



