THE KNEE-JOINT. 



187 



Capsnlar membrane. Under this name is described the fibrous membrane 

 which invests the joint in the intervals between the stronger bands which have been 

 named ligaments. It is incomplete, not extending underneath the tendon of the 

 extensor muscle. Between the sides of the patella and the femur it consists of 

 fibres connected with the insertions of the vasti muscles and with the fascia lata, 

 and thus forms the structures which have been called lateral patellar ligaments. 

 Posteriorly it is thin, covering the condyles of the femur beneath the gastrocnemius 

 muscle, and it frequently presents an aperture beneath the inner head of that 

 muscle, through which the bursa under the semimembranosus tendon is put into 

 communication with the joint-cavity. 



The synovial membrane is the largest in the body. Traced downwards from 

 the femur on either side of the joint, it may be followed along the capsule to the 



Fig. 213. THE SUPERFICIAL PARTS OP 'THE KNEE-JOINT REMOVED, AND THE EXTERNAL CONDYLE OP 



THE FEMUR SAWN OFF OBLIQUELY, TOGETHER WITH HALF THE PATELLA, SO AS TO EXPOSE BOTH 

 THE CRUCIAL LIGAMENTS TOGETHER. (Allen Thomson.) J 



In A, the parts are in the position of extension, in B, that of flexion, the figures being designed to 

 show the different states of tension of the crucial ligaments in these positions. 1, sawn surface of 

 femur ; 2, sawn surface of patella ; 3, ligamentuui patellae ; 4, anterior or external crucial ligament, 

 tense in A. and relaxed in B ; 5, posterior or internal crucial ligament, partly relaxed in A, tense in B ; 

 6, internal, and 7, external semilunar fibro-cartilage ; 8, transverse ligament ; 9, articular surface of the 

 tibia, extending behind the external semilunar fibro-cartilage ; 10, on the head of the fibula, points to 

 the anterior superior tibio-peroneal ligament ; 1 1, upper part of the interosseous membrane. 



upper surfaces of the semilunar fibro-cartilages, round the free borders of those 

 structures to their inferior surfaces, and thence to the tibia. The crucial ligaments 

 are invested in front by a reflected portion of the membrane continued forwards 

 from the posterior wall of the joint. Between the tibia and patella the synovial 

 membrane lies upon a large pad or cushion of fat, on the surface of which it forms 

 two lateral folds (alar ligaments} which pass to the side and upwards along the 

 lower border of the articular surface of the patella, while from the middle of the pad it 

 sends backwards a variably developed process, the mucous ligament, through the joint 

 to the front of the intercondylar fossa. Above the patella the synovial membrane 

 extends upwards for a short distance under the extensor tendon, and the pouch thus 

 formed communicates in most cases more or less freely with a bursa situated here 

 between the tendon and the anterior surface of the feinur. 



