KNEE JOINT. 133 



extremities of the external cartilage being inserted into the same 

 fossa, form almost a complete circle, and the cartilage being some- 

 what broader than the internal, nearly covers the articular surface of 

 the tibia. The external semilunar fibre-cartilage besides giving off a 

 fasciculus from its anterior border to constitute the transverse liga- 

 ment, is continuous by some of its fibres with the extremity of the 

 'anterior crucial ligament ; posteriorly it divides into three slips, one, 

 a strong cord, ascends obliquely forwards and is inserted into the 

 anterior part of the inner condyle in front of the posterior crucial 

 ligament ; another is the fasciculus of insertion into the fossa of the 

 spinous process ; and the third, of small size, is continuous with the 

 posterior part of the anterior crucial ligament. 



The ligamentum mucosum is a slender conical process of syno- 

 vial membrane enclosing a few ligamentous fibres which proceed 

 from the transverse ligament. It is connected by its apex, with the 

 anterior part of the condyloid notch, and by its base is lost in the 

 mass of fat which projects into the joint beneath the patella. 



The alar ligaments are two fringed folds of synovial membrane, 

 extending from the ligamentum mucosum, along the edges of the 

 mass of fat to the sides of the patella. 



The synovial membrane of the knee joint is by far the most exten- 

 sive in the skeleton. It invests the cartilaginous surface of the 

 condyles of the femur, of the head x>f the tibia, and of the inner 

 surface of the patella ; it covers both -surfaces of the semilunar 

 fibro-cartilages, and is reflected upon the crucial ligaments, and 

 upon the inner surface of the ligaments which form the circum- 

 ference of the joint. On each side of the patella, it lines the tendi- 

 nous aponeuroses of the vastus internus and vastus externus muscles, 

 and forms a pouch of considerable size between the extensor tendon 

 and the front of the femur. It also forms the folds in the interior of 

 the joint, called " ligamentum mucosum," and " ligamenta alaria." 

 The superior pouch of the synovial membrane is supported and 

 raised during the movements of the limb by a small muscle, the 

 subcrureus which is inserted into it. 



Beneath the ligamentum patellae and the synovial membrane is 

 a considerable mass of fat, which presses the membrane towards 

 the interior of the joint, and occupies the fossa between the two 

 condyles. 



Besides the proper ligaments of the articulation, the joint is pro- 

 tected on its anterior part by the fascia lata, which is thicker upon 

 the outer than upon the inner side, by a tendinous expansion from 

 the vastus internus, and by some scattered ligamentous fibres which 

 are inserted into the sides of the patella. 



Actions. The knee joint is one of the strongest of the articula- 

 tions of the body, while at the same time it admits of the most per- 

 fect degree of movement in the directions of flexion and extension. 

 During flexion the articular surface of the tibia glides forward on 

 the condyles of the femur, the lateral ligaments, the posterior, and 

 crucial ligaments are relaxed, while the ligamentum patelte being 



