THE UPPER TIBIOFIBULAR ARTICULATION 151 



The movements of the patella are partly gliding and partly 

 those of coaptation. In extension only the lower sixth of the 

 patellar articular surface is in contact with the femur; in semi- 

 flexion, the middle three-sixths; in full flexion, the upper two- 

 sixths, as the ligamentum patella? pulls it down in front of 

 the joint. 



The Synovial Membrane. It encloses the articular cavity of 

 the knee-joint. It is the largest and most extensive synovial 

 membrane in the body, consisting of a cul-de-sac beneath 

 the quadriceps extensor tendon, which communicates by a 

 small orifice with a synovial bursa between the patella and 

 femur (bursa subpatellaris). It extends beneath the vastus 

 internus and externus muscles, and is separated from the 

 anterior ligament by the capsule and adipose tissue (infra- 

 patellar pad). In this region it gives off a triangular pro- 

 longation containing a few ligamentous fibers, the ligamentum 

 mucosum, which extends from below the patella to the inter- 

 condyloid notch; the latter gives off two thin folds, ligamen- 

 tum alaria, which extend laterally between the femur and 

 patella. The membrane covers the internal surfaces of the 

 ligaments, surrounds the crucial ligaments and cartilages. The 

 portion between the quadriceps extensor muscle and the femur 

 is supported during the movements of the knee by the sub- 

 crureus muscle, which is inserted into the upper part of the 

 capsular ligament. It forms a cul-de-sac between the groove 

 on the back of the external semilunar cartilage and the popliteus 

 muscle. 



THE LIGAMENTS BETWEEN THE BONES OF THE LEG 



The Upper Tibiofibular Articulation 



The capsule rises from the tibia about \ inch (5 mm.) above 

 the articular surface, elsewhere from its edge; it passes to the 

 contiguous margins of the fibular surface, and generally en- 

 closes a little space at the lower part of the joint, covered 

 only by periosteum, where the tibia and fibula rest upon each 

 other. 



Accessory bands are anterior and posterior ligaments (liga- 

 menta capituli fibulae anteria et posteria). The former consists 

 of one or more bands from the front of the head of the fibula 



