434 SURGICAL APPLIED ANATOMY. [Chap. xxi. 



This is the largest bursa in the space, and after adult 

 life it usually communicates with the joint. It is, of 

 all the bursse in this region, the one most often 

 enlarged, and when affected may attain great size. 

 In one reported case the sac measured 5 inches by 3*5 

 inches. In the extended position of the limb the 

 enlarged bursa feels firm and resisting, but on flexion 

 it becomes flaccid and can often be made to entirely 

 disappear. Probably the slit - like communication 

 between the bursa and the joint is closed when the 

 posterior ligament is tightened by extension, and is 

 opened when it is relaxed on bending the knee. In 

 the latter posture the contents of the bursa can be 

 reduced into the cavity of the knee-joint, and so the 

 tumour disappears. (2) A little bursa between the 

 semimembranosus tendon and the tuberosity of the 

 tibia. It never communicates directly with the joint, 

 but has sometimes an opening into the bursa just 

 described. Outer side. (1) A bursa between the 

 popliteus tendon and the external lateral ligament 

 that does not usually communicate with the joint. 

 (2) One between the popliteus tendon and outer 

 tuberosity of the tibia, that is merely a diverticulum 

 from the synovial membrane. This sac may open 

 into the tibio-fibular articulation, and so bring that 

 cavity in connection with the knee-joint. (3) A bursa 

 between the outer head of the gastrocnemius and the 

 femoral condyle. It is not constant and is not con- 

 nected with the articulation. (4) A bursa between 

 the biceps tendon and the external lateral ligament. 

 The peroneal nerve runs across this sac, a circum- 

 stance that may explain some of the pain experienced 

 when the bursa is enlarged. 



It is not improbable that wounds of bursse in 

 this region containing fluid have been mistaken for 

 wounds of the joint, and the escaping serum for 

 synovia. 



