43 SURGICAL APPLIED ANATOMY. [Chap. xxi. 



knee. Beneath the skin and superficial tissue is the 

 popliteal fascia, a dense membrane that covers in the 

 space. It is but a continuation of the fascia lata of 

 the thigh, and is continuous below with the fascia of 

 the leg. It passes without bony attachment over the 

 hamstring muscles that bound the ham. This fascia 

 limits, often in a very marked manner, the progress of 

 popliteal abscesses and growths towards the surface. 

 Its unyielding character is a prime cause in the pro- 

 duction of the severe pain with which such collections 

 and tumours are often associated. The popliteal 

 abscess, unable to reach the surface, is encouraged to 

 extend either up into the thigh or down the leg. The 

 ham may hold a very considerable quantity of pus. 

 Yelpeau has seen a case where a litre (1 pint, 15 ozs.) 

 of pus was evacuated from this region in a patient 

 who presented before the operation but an insignificant 

 swelling in the site of the collection. Duplay records 

 two cases of ulceration of an abscess into the popli- 

 teal artery, and Ollivier an instance where the abscess, 

 unable to find a way to escape, ultimately entered 

 into the knee-joint. 



Pus may reach the ham from the buttock or pelvis 

 by following the great sciatic nerve, or may extend 

 from the thigh through the opening in the great 

 adductor for the femoral vessels. 



The hamstring muscles are frequently found 

 contracted in neglected cases of knee-joint disease, and 

 produce thereby more or less rigid flexion of the leg 

 upon the thigh. Among the reasons for this contrac- 

 tion may be mentioned the fact that these muscles 

 are all supplied by the great sciatic nerve, and that 

 the knee-joint derives its main nerve -supply from 

 the same trunk by means of its internal popliteal 

 branch. 



Contraction of these muscles in knee-joint disease 

 tends not only to flex the knee but also to draw the 



