THE KNEE. 5, 



of the tibia, and the middle of the ankle should be in the same 

 straight line. A useful point in the adjustment of fractures. 

 Behind the upper half of the ligamentum patellae is the 

 synovial membrane of the knee-joint ; behind the lower half 

 is a synovial bursa and a pad of fat. It is well to remember 

 this in cases of injury to the ligamentum patellae. 



109. Patellar bursa. The patellar or housemaids' bursa 

 is situated not only over the patella, but over the upper part 

 of the ligament. This is plain enough when the bursa 

 becomes enlarged. There is another subcutaneous bursa 

 over the insertion of the ligament into the tubercle of the 

 tibia. This is quite independent of the deep bursa between 

 the tendon and the bone. 



1 IO. Synovial membrane of knee. The synovial mem- 

 brane of the knee, when the joint is extended, rises like a 

 cul-de-sac above the upper border of the patella about two 

 inches- It ascends, too, a little higher under the vastus 

 internus than the vastus externus a fact very manifest 

 when the joint is distended. When the knee is bent this 

 cul-de-sac is drawn down hence the rule of bending the 

 knee in operations near the lower end of the femur. 



The lower level of the synovial membrane of the knee is 

 just above the level of the upper part of the head of the 

 fibula. The tibio-fibular synovial membrane is, with rare 

 exceptions, independent of that of the knee. 



111. Popliteal tendons The tendons forming the 

 boundaries of the popliteal space can be distinctly felt when 

 the muscles which bend the knee are acting. On the outer 

 side, we have the biceps running down to the head of the 

 fibula. On the inner side we feel three tendons, disposed as 

 follows : nearest to the middle of the popliteal space is the 

 semitendinosus, very salient and traceable high up the thigh ; 

 next comes the thick round tendon of the semimembranosus ; 

 still more internally is the gracilis. The sartorius, which 

 forms a graceful muscular prominence on the inner side of 

 the knee, does not become tendinous until it gets below it. 



112. Popliteal bursa. The precise position of the bursa 

 in the popliteal space, which sometimes enlarges to the size 



