POPLITEAL FOSSA 311 



and its branches must now be cleaned. Pull the tibial nerve 

 laterally and clear away the fat on the lateral side of the semi- 

 membranosus at the proximal part of the fossa. The artery 

 enters the fossa a little distal to the proximal angle, on the medial 

 side, where it lies close to the floor or anterior boundary of the 

 fossa. It leaves the fossa at the distal angle at the distal border 

 of the popliteus muscle. In the proximal part of the fossa the 

 vein is lateral to the artery. In the middle part of the fossa 

 it is posterior to the artery, and in the distal part it is medial 

 to the artery, always intervening between the artery and the tibial 

 nerve. In the angle between the artery and the vein, in the 

 proximal part of the fossa, look for the slender genicular branch 

 of the obturator nerve, and, having secured it, follow it to the point 

 where it pierces the posterior ligament of the knee joint with 

 the middle genicular artery. Then proceed to clean the popliteal 

 artery and its branches and the popliteal vein. Not uncommonly 

 in addition to the main vein, whose position has been described, 

 there are two or more accessory venous channels which com- 

 municate with the main vein and anastomose with one another 

 round the artery ; if they are present clear them away, but take 

 care, whilst doing so, not to injure the branches of the artery. 

 The branches of the artery to the hamstring muscles and the 

 muscles of the calf are numerous, and, if they interfere with 

 the cleaning of the main structures, they must be divided, but 

 the articular branches must be carefully preserved ; they are 

 five in number, the superior and inferior medial genicular 

 arteries, the superior and inferior lateral genicular arteries, and 

 the middle genicular artery. They all lie close to the floor of 

 the space and are liable to be injured as the soft fat around the 

 popliteal artery is cleared away. The superior genicular branches 

 lie at the level of the proximal borders of the condyles of the 

 femur. They run transversely and they leave the space, the 

 medial by piercing the posterior intermuscular septum of the 

 thigh, and the lateral by piercing the lateral intermuscular 

 septum. The inferior lateral genicular artery also runs trans- 

 versely, at the level of the interval between the lateral condyle of 

 the femur and the head of the fibula, but the inferior medial 

 genicular branch descends obliquely, deep to the medial head of 

 the gastrocnemius, and then turns forwards, distal to the medial 

 condyle of the tibia. The middle genicular artery accompanies the 

 genicular branch of the obturator nerve through the middle part 

 of the posterior ligament of the knee joint. The final step of 

 the dissection is the cleaning of the fat from the floor of the 

 fossa. With the handle of the scalpel scrape the fat away from 

 the posterior surface of the femur, the posterior ligament of the 

 knee joint, and the posterior surface of the fascia covering the 

 popliteus, taking care not to injure the genicular arteries. 



Floor of the Fossa. The floor is formed proximo-distally 

 by (i) the popliteal surface of the femur; (2) the oblique 

 popliteal ligament of the knee joint ; and (3) by the strong 

 fascia which covers the popliteus muscle. 



The Fossa Poplitea as seen in a Section through the Frozen Knee. 



The diamond -shaped space on the back of the knee joint which is brought 



