FOSSA POPLITEA 239 



defined and cleaned, the contents should be dissected by removing the soft 

 fat which surrounds them. 



The dissection of the fossa should be carried out over the entire area at 

 the same time. The heads of the gastrocnemius muscle, therefore, should 

 be well separated from each other. It is here that the dissection becomes 

 tedious, because the numerous branches of the nerves and vessels to the 

 muscles on the back of the leg require time and care for their dissection. 



The floor of the fossa must now be cleaned. Scrape the fatty tissue 

 from the popliteal surface of the femur with the handle of the knife. 



It is during this stage of the dissection that the genicular branches of 

 the popliteal artery are liable to injury, as they lie in close contact with the 

 floor. Be especially careful not to injure the medial artery of the knee 

 which pierces the posterior part of the capsule of the joint, and* the superior 

 arteries of the knee which wind round the femur, immediately proximal 

 to the condyles. The fascia covering the popliteus muscle should be 

 left in position. 



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 

 into view by dissection, differs widely from the condition which is observed 

 when transverse sections are made through this part of the frozen limb 

 (Fig. 88). Before the integuments and fasciae are removed all the parts 

 are tightly braced together, and the fossa poplitea is merely represented by 

 a small intermuscular interval between the lower parts of the hamstring 

 muscles. The fossa in this condition is rather under an inch wide at its 

 broadest part. The popliteal artery, therefore, as it traverses the space, 

 is covered by muscles throughout its whole course, with the exception of a 

 very small part immediately above the knee-joint. 



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

 distally by (i) the planum popliteum of the femur; (2) the 

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

 strong fascia which covers the popliteus muscle. 



Nervus Cutaneus Femoris Posterior (O.T. Small Sciatic). 

 This nerve enters the fossa poplitea at its proximal angle, and 

 proceeds distally, immediately subjacent to the fascia poplitea. 

 It gives one or two twigs through the fascia to the skin, and 

 finally pierces the fascia in the distal part of the fossa. Its 

 terminal twigs are distributed to the skin over the proximal 

 part of the calf of the leg. 



Nervus Tibialis (O.T. Internal Popliteal Nerve). This 

 nerve enters the popliteal fossa, by emerging from under cover 

 of the biceps femoris, and runs distally so as to bisect the fossa 

 longitudinally. It is the larger of the two terminal branches of 

 the sciatic nerve, and it arises about the middle of the thigh. 

 At the lower border of the popliteus muscle it leaves the fossa 

 poplitea and passes into the posterior region of the leg. The 

 superficial position of the tibial nerve has already been 

 referred to. At first upon the lateral side of the popliteal 

 vessels it crosses them superficially, and in the distal part of 



