226 ARTICULATIONS. 



iween the anterior convex margin of the external semilunar cartilage, to the 

 anterior extremity of the internal cartilage ; its thickness varies considerably in 

 different subjects. 



The Coronary Ligaments consist of numerous short fibrous bands, which con- 

 nect the convex border of the semilunar cartilages with the circumference of the 

 head of the tibia, and with the other ligaments surrounding the joint. 



The Synovial Membrane of the knee-joint is the largest and most extensive in 

 the body. Commencing at the upper border of the patella, it forms a large cul- 

 de-sac beneath the Extensor tendon of the thigh : this is sometimes replaced by a 

 synovial bursa interposed between the tendon and the front of the femur, which 

 in some subjects communicates with the synovial membrane of the knee-joint, by 

 an orifice of variable size. On each side of the patella, the synovial membrane 

 extends beneath the aponeurosis of the Vasti muscles, and more especially beneath 

 that of the Vastus internus ; and, beneath the patella, it is separated from the 

 anterior ligament by a considerable quantity of -adipose tissue. In this situation, 

 it sends off a triangular-shaped prolongation, containing a few ligamentous fibres, 

 which extends from the anterior part of the joint below the patella, to the front 

 of the intercondyloid notch. This fold has been termed the ligamentum mucosum. 

 The ligamenta alaria consist of two fringe-like folds, which extend from the sides 

 of the ligamentum mucosum, upwards and outwards, to the sides of the patella. 

 The synovial membrane invests the semilunar fibre-cartilages, and on the back 

 part of the external one forms a cul-de-sac between the groove on its surface and 

 the tendon of the Popliteus ; it is continued to the articular surface of the tibia, 

 surrounds the crucial ligaments, and the inner surface of the ligaments which 

 inclose the joint ; lastly, it approaches the condyles of the femur, and from them is 

 continued on to the lower part of the front of the shaft. The pouch of synovial 

 membrane between the Extensor tendon and front of the femur is supported, 

 during the movements of the knee, by a small muscle, the Subcrureus, which is 

 inserted into it. 



The Arteries supplying the joint are derived from the anastomotic branch of 

 the femoral, articular branches of the popliteal, and recurrent branch of the 

 anterior tibial. 



The Nerves are derived from the obturator, anterior crural, and external and 

 internal popliteal. 



Actions. The chief movements of this joint are flexion aud extension ; but it is 

 also capable of performing some slight rotatory movement. During flexion, the 

 articular surfaces of the tibia, covered by their interarticular cartilages, glide 

 backwards upon the condyles of the femur, the lateral, posterior, and crucial liga- 

 ments are relaxed, the ligamentum patellas is put upon the stretch, the patella 

 filling up the vacuity in front of the joint between the femur and tibia. In 

 extension, the tibia and interarticular cartilages glide forwards upon the femur; 

 all the ligaments are stretched, with the exception of the ligamentum patellae, 

 which is relaxed, and admits of considerable lateral movement. The movement 

 of rotation is permitted when the knee is semi-flexed, rotation outwards being 

 most extensive. 



3. AETICULATIOIST BETWEEN THE TIBIA AND FIBULA. 



The articulations between the tibia and fibula are effected by ligaments which 

 connect both extremities, as well as the shaft of these bones. They may, con- 

 sequently, be subdivided into three sets. 1. The Superior Tibio-fibular articula- 

 tion. 2. The Middle Tibio-fibular articulation. 3. The Inferior Tibio-fibular 

 articulation. 



1. SUPEEIOR TIBIO-FIBULAR ARTICULATION. 

 This articulation is an arthrodial joint. The contiguous surfaces of the bode." 



