POPLITEAL FOSSA 309 



The distal boundaries will be cleaned and displayed as some of 

 the contents of the fossa are secured and followed towards their 

 terminations. 



Clean first the proximal lateral boundary. Make an incision 

 through the deep fascia along its medial margin, turn the fascia 

 laterally and expose the biceps femoris. Clean the muscle and its 

 tendon, follow the tendon to its insertion into the head of the 

 fibula, and note that at the level of the knee the biceps femoris 

 crosses the lateral head of the gastrocnemius. After the distal part 

 of the biceps femoris has been cleaned, turn to the proximal medial 

 border of the space ; make an incision through the deep fascia 

 along its lateral margin, and reflect the fascia covering it towards 

 the medial side to expose the semitendinosus and semimem- 

 branosus muscle; follow the tendon of the more superficial 

 semitendinosus muscle to the level of the medial condyle 

 of the tibia. Then pull the semitendinosus aside and clean the 

 distal part of the semimembranosus, and follow its tendon 

 to its insertion into the medial condyle of the tibia. Pre- 

 serve if possible the muscular branches of the popliteal artery 

 which enter the lateral part of the muscle, and note that the 

 tendon of insertion springs mainly from the lateral border and 

 anterior (deep) surface of the muscle. Pull the part of the 

 muscle which lies at the level of the medial condyle of the femur 

 towards the medial side of the knee and display the semi- 

 membranosus bursa, which lies between the semimembranosus 

 and the medial head of the gastrocnemius as they cross one 

 another. The semimembranosus bursa often communicates, 

 round the medial border of the gastrocnemius, with a bursa 

 which lies between the medial head of the gastrocnemius and 

 the back of the knee joint, and that, in turn, communicates with 

 the cavity of the knee joint. Open the bursa and, if possible, 

 display the communications which have been mentioned with 

 the aid of a probe. Now pull the semitendinosus and semi- 

 membranosus laterally and clean the gracilis, which lies medial 

 and anterior to them. At the anterior border of the gracilis 

 the saphenous nerve emerges between the gracilis and the 

 posterior border of the sartorius accompanied by the saphenous 

 branch of the arteria genu suprema ; secure the artery and 

 nerve and follow them downwards to the medial border of the 

 tibia and note that they accompany the great saphenous vein, 

 which was exposed when the medial side of the thigh was 

 dissected. Then pull the gracilis medially and clean the distal 

 part of the adductor magnus which lies lateral to it. 



When the proximal boundaries of the fossa have been cleaned 

 and examined, seize the posterior cutaneous nerve of the thigh 

 at the point where it pierces the popliteal fascia (see p. 306), and 

 follow it to the proximal angle of the fossa, dividing the popliteal 

 fascia which lies superficial to it ; then remove the remains of 

 the popliteal fascia from the proximal part of the popliteal area. 

 Now pull the posterior cutaneous nerve aside, with a hook, and 

 cut through the fat in the proximal apex of the fossa till the 

 large tibial nerve is exposed. Follow the tibial nerve distally, 

 cleaning it, partly with the aid of the handle of the scalpel and 

 partly by occasional touches with the point of the scalpel, and 

 secure its cutaneous, muscular, and articular branches. Its 

 cutaneous branch, the medial cutaneous nerve of the calf, arises 



