MO^^EMEXTS OF THE KXEE-JOTXT. 



171 



indication of the original separation of the synovial membranes of the inner and 

 outer joints, and the cnacial ligaments may be looked upon as the external and 

 internal lateral ligaments of those two joints respectively. Each portion of the 

 articular surface of the femur belongs either to one or other of the tkree com- 

 ponent joints of the knee, and no part is common to any two of them. On a 

 well-marked femur, the inferior limits of the patellar surface are quite distia- 

 guishable ; the Hne which separates this surface from the outer tibial joint 

 passing directly between it and the condyle, and that which separates it from 

 the Luner joint being continued backwards, so as to cut off from the rest of the 

 inner condyle a naixow tract at the side of the intercondylar fossa. 



Fis. 153. 



Fig. 153. — The superficial taiits of the Knee-Joint removed, and the extei-nal 

 Condyle op the Fejiuh sawn off obliquely, together, with half the patella, 

 so as to expose both the crucial ligaments together. (A. T.) ^ 



lu A, the parts are in the position of extension, in B, that of flexion, the figures being, 

 designed to sho^v the different state of tension of the crucial hgaments in these positions. 

 1, sawn surface of the femur ; 2, sawn surface of the patella; o, hg.imentum patelke ; 

 4, anterior or external crucial Hgameut, tense in A, and relaxed in Ij ; 5, posterior or 

 internal cnicial ligament, relaxed in A, tense in 1> ; 6, internal, and 7, external semilunar 

 cartilage ; 8, transverse ligament ; 9, articular surface of the tibia, extending behind the 

 external semilunar cartilage ; 10, on the head of the fibula, points to the anterior superior 

 tibio-peroneal ligament ; 11, upper part of the interosseous membrane. 



Tlie movement of the patella on the femur is one partly of glidm g. jjartly of 

 coaptation. This is illustrated by a careful examination of the articular surface 

 of the patella, which is not unifonnly curved from above downwards, as it would 

 be, were the movement one of gliding only, but exhibits on each side of the 

 vertical ridge three veiy slightly depressed surfaces, separated by two shghfc 

 transverse elevations, and along the inner margin a seventh area, upon which 

 the transverse lines do not encroach (Goodsir.) When the knee is extended, and 

 the patella draAvn upwards by the extensor muscles, the two inferior facets of 

 the patella are in contact with the upper margin of the femoral surface ; in 

 semiflexion the middle facets only are in contact with the femur ; in gi-eater 

 flexion, the supeiior parts of the pateUa are in contact with the lower part of 



