3i2 THE INFERIOR EXTREMITY 



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. 133). Before the integuments and fasciae are removed all the parts 

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

 a small intermuscular interval between the distal 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 proximal to the knee joint. 



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

 The posterior cutaneous nerve of the thigh enters the popliteal 

 fossa at its proximal angle, and passes distally, immediately 

 subjacent to the deep fascia. 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). The tibial 

 nerve enters the fossa at its proximal angle, emerging from 

 under cover of the biceps femoris. It runs vertically down- 

 wards to the distal angle and thus bisects the fossa 

 longitudinally. It commences about the middle of the thigh 

 as the larger of the two terminal branches of the sciatic 

 nerve, and it leaves the fossa at the lower border of the 

 popliteus muscle, and enters the posterior region of the leg. 

 Its superficial position in the fossa has already been referred 

 to. When it enters the fossa it lies on the lateral side of the 

 popliteal vessels, at the mid-length of the space it crosses 

 superficial to them, and in the distal part of the space it is 

 medial to them ; consequently the muscular branches given off, 

 in the lower part of the fossa, to the lateral head of the 

 gastrocnemius, the plantaris, the soleus, and the popliteus 

 pass posterior to the vessels on their way to the muscles they 

 supply. 



The branches of the nerve in the popliteal fossa are 

 classified as cutaneous, muscular, and articular. 



The medial cutaneous nerve of the calf is the cutaneous 

 branch. It arises about the middle of the fossa, and pro- 

 ceeds distally in the furrow between the two heads of the 

 gastrocnemius. It will afterwards be seen to unite with the 

 peroneal anastomotic nerve, a little distal to the middle of the 

 calf of the leg, to form the nervus suralis (Fig. 127). 



The muscular branches supply both heads of the gastro- 

 cnemius, the plantaris, the soleus, and the popliteus : they 

 come off in the distal part of the fossa. The branch to the 



