SYNOVIAL SAC AND FAT AROUND KNEE. 637 



raent may be removed, to show the pouches of the synovial membrane 

 which project behind over the condyles of the femur ; but the limb is to 

 be replaced in the former position before the parts are learnt. 



The synovial membrane (fig. 218) lines the interior of the capsule, and 

 is continued to the articular ends of the bones. It invests the interarticular 

 cartilages after the manner of serous membranes, and sends a pouch be- 

 tween the tendon of the popliteus and the external fibro-cartilage and the 

 head of the tibia ; it is also reflected over the strong crucial ligaments at 

 the back of the joint. 



There are three named folds of the synovial membrane. One in the 

 centre of the joint is the mucous ligament (), which contains small ves- 

 sels and some fat, and extends from the interval between the condyles to 

 the fat below the patella. Below and on each side of the patella is another 

 fold alar ligament (b and c), which is continuous with the former below 

 the patella, and is placed over a mass of fat : the inner (6) is prolonged 

 farther than the outer by a semilunar piece of the serous membrane. 



At the back and front of the articulation pouches are prolonged beneath 

 the tendons of muscles. Behind there are two, one on each side, between 

 the condyle of the femur and the tendinous head of the gastrocnemius. 

 On the front, the sac projects under the extensor muscle one inch above 

 the articular surface ; and if it communicates with the bursa in that situa- 

 tion, it will reach two inches above the joint surface of the femur. When 

 the joint is bent there is a greater length of the serous sac above the patella. 



Fat around the joint. Two large masses are placed above and below r 

 the patella, and some fat is located around the crucial ligaments. 



The infra-patellar mass, the largest of all, fills the interval between the 

 patella with its ligament and the head of the tibia, and gives origin to the 

 ridges of the synovial membrane. From it a piece is continued around 

 the patella : but it is larger at the inner margin of the bone, than on the 

 outer, and overhangs the inner perpendicular facet. During extension of 

 the joint the infra-patellar pad is applied to, and lubricates the articular 

 surfaces of the femur. 



The supra-patellar pad is interposed between the triceps extensor and 

 the femur around the top of the synovial sac, and is greater on the outer 

 than on the inner side. 



Dissection (fig. 219). The ligamentous structures within the capsule 

 will be brought into view, whilst the limb is still in the same position, by 

 throwing down the patella and its ligament, and clearing away the fat 

 behind it. In this step the student must be careful of a small transverse 

 band which connects anteriorly the interarticular cartilages. 



The remains of the capsule and other ligaments, and the synovial mem- 

 brane are next to be cleared away from the front and back of the crucial 

 ligaments, and from the interarticular cartilages. Whilst cleaning the 

 posterior crucial the limb is to be placed flat on the table with the patella 

 down ; and the student is to be careful of a band before it from the exter- 

 nal fibro-cartilage, or of two bands, one before and the other behind it. 



Ligaments ivithin the capsule. The ligamentous structures within the 

 capsule consist of the central crucial ligaments, and of two plates of fibro- 

 cartilage on the head of the tibia. 



The crucial ligaments (fig. 219) are two strong fibrous cords between 

 the ends of the tibia and femur, which maintain in contact the bones. 

 They cross one another somewhat like the legs of the letter X, and have 



