THE KNEE-JOINT. 



405 



intercondylar notch. The fibres from the external semilunar cartilage run along it 

 in a varying position, but usually as a well-defined bundle. When the joint is 

 straight the surface of the anterior ligament looks approximately forward and up- 

 ward, its line of insertion being about vertical ; when it is fully flexed the outer 

 edge is brought forward so that the ligament is somewhat twisted on itself and the 

 upper part looks inward, the line of insertion slanting slightly downward and back- 

 ward. In the former position the posterior crucial has the anterior surface looking 

 outward, forward, and downward, the line of insertion being horizontal, with the 

 front external. With the knee flexed the ligament is closely applied to the internal 

 condyle. 



The Subpatellar Fat, the Ligamentum Mucosum, and the Ligamenta 

 Alaria (Figs. 419, 423 j. — If the joint be opened by dividing the capsule just above 



Fig. 420. 



Patellar surface 



Capsule reflected 



External condyle 



Ant. crucial ligament 



Ext. semilunar cartilage 



Transverse ligament' 

 Coronary ligament 

 Edge of superior surface of tibia 



Capsule reflected 



Post crucial ligament 



Internal condyle 



Interna! semilunar 

 cartilage 



Coronary ligament 



Bursa beneath ligamentum patellae 



'jL — Tuberosity of tibia 

 Right knee-joint, opened and the knee flexed. Seen from before. 



the patella, or, better, by splitting the patella and turning one-half to either side, a 

 large mass of fat is seen inside the capsule, below the patella and above the front 

 and top of the tibia, covered by the synovial membrane. This mass has a definite 

 shape, though, of course, subject to change by pressure. It is perhaps best described 

 as pyramidal, the base being towards the surface between the knee-pan and the tibia. 

 When the knee is straight it fills the patellar surface of the femur and laterally 

 passes under the condyles, filling the space between them and the tibia. It reaches 

 to the semilunar cartilages. Towards the joint it has two free angles, a larger one 

 below entering between the bones as just described and a smaller one above. The 

 lateral halves, including the synovial covering, are called the alar ligaments ' (Figs. 

 419, 423). From the middle of this mass below the patella runs a collection of fat 

 with areolar and elastic tissue, invested by synovial membrane, to the top of the inter- 

 condylar notch. This is the ligamentum mucosum/ of litde strength and not 

 absolute constancy, which acts as a guy, preventing the mass of fat from falling 

 away from the femur. There are also collections of fat about the crucial ligaments 

 and at the back of the joint between the posterior crucial and the capsule. 



The synovial membrane lines the capsule in a general way, but is separated 



' PHcae alares. ^ PHca synovialis patellae. 



