4o8 



HUMAN ANATOMY. 



of the capsule, and on reaching its insertion it makes a more or less prominent pro- 

 jection into the joint. There may or may not be a projection of the capsule like a 

 bursa at the point where the two are fused. On its way the tendon often sends 

 some fibres to the posterior crucial ligament. 



Movements. — The motions between the femur and the patella will be consid-i 

 ered after those between the thigh and the leg. The knee cannot be a hinge-joint, 

 for in such the movilig part is always at the same distance from the axis of rotation, 

 which is out of the question in the knee, owing to the shape of the condyles. The 

 fact that these are neither of equal length nor parallel complicates the problem. The 

 joints are further subdivided by the semilunar cartilages, which make a slight 

 socket for each condyle. This socket is more or less movable and also compressible 

 and elastic, so that it may change its shape to accommodate itself to the form of 



Fig. 423. 



Tendon of extensor quadriceps 



Capsule 



Ligamentum mucosum 



External condyle 



Alar ligament 



Ligamentum patellae 



Capsule 

 Post, crucial ligament 



Internal condyle 

 Alar ligament 



Tubercle of tibia 



Patella removed from right knee, which is strongly flexed to show alar ligaments and ligamentum mucosum. A 



probe is passed beneath the latter. 



different parts of the condyle. The external semilunar cartilage, having its horns 

 securely attached near together and having a long coronary ligament, can swing 

 backward and forward pretty freely as a whole. The internal cartilage is more 

 closely fastened to the tibia, excepting the anterior horn, which has no constant 

 arrangement. Not only can the semilunar cartilages change shape, but, as Braune 

 has shown, the cartilage of the joint is capable of compression. For all these 

 reasons accurate mathematical statements are impossible. 



In extension of the leg on the thigh, beginning with the knee flexed, the tibia 

 travels along the irregular curve of the condyles, carrying the semilunar cartilages 

 with it. There is practically no movement between the internal cartilage and the 

 tibia, unless at the end, and probably little beneath the external. The external 

 tuberosity of the tibia reaches the front of the shorter condyle before the internal 

 tuberosity has completed its course. The last part of the advance of the latter is 

 accompanied by an outward rotation of the tibia on a vertical axis passing through 

 about the middle of the outer condyle, so that while the inner tuberosity still swings 



