THE LOWER LIMB 537 



From the posterior ligament the sjmovial membrane is reflected 

 forwards in the form of two laminae, one of which passes over the 

 outer surface of the anterior crucial ligament, and the other over 

 the inner surface of the posterior crucial ligament. After having 

 done so, these two laminae become continuous with each other in 

 front of the crucial ligaments. It will thus be evident that the 

 following parts of these hgaments are destitute of synovial 

 membrane : (i) the posterior surface of each Ugament, and (2) 

 that part of the anterior surface of the posterior ligament which is 

 in contact with the anterior ligament. 



In connection with the posterior ligament of the knee-joint it 

 is to be noted that there is a narrow median vertical zone which 

 is destitute of synovial membrane, on account of the forward reflec- 

 tion of that membrane in two laminae. This interlaminar zone is 

 covered by a certain amount of fat. 



The synovial membrane furnishes an investment to the tendon 

 of the popliteus, which separates that tendon from the long external 

 lateral ligament. This prolongation also extends in a downward 

 direction between the posterior part of the external semilunar 

 fibro-cartilage and the outer tuberosity of the tibia, so as to facilitate 

 the movement of the tendon of the popliteus at that point. It 

 may extend so far down as to become continuous with the synovial 

 membrane of the superior tibio-fibular joint. At the back of the 

 joint the synovial membrane frequently communicates with the 

 popliteal bursa between the semimembranosus and inner head of 

 the gastrocnemius. 



The synovial membrane, as it covers the infrapatellar pad of 

 fat, forms three folds — the ligamentum mucosum and ligamenta 

 alaria. The ligamentum mucosum, which contains a little fat, 

 extends backwards to be attached to the front part of the inter- 

 condylar fossa of the femur. It is narrow and pointed at its 

 femoral attachment, but over the infrapatellar pad of fat it 

 widens out and becomes triangular. The lateral borders of this 

 latter part of the ligamentum mucosum constitute the so-called 

 ligamenta alaria, which extend for a short distance in an upward 

 direction along the lateral margins of the patella. 



The ligamentum mucosum, which serves to adjust the infra- 

 patellar pad of fat to the different positions of the joint, is the 

 remains of the double synovial partition which originally separates 

 the femoro-tibial articulations. 



The articular fat forms two chief collections, called infrapatellar 

 and suprapatellar, which represent the Haversian glands of the 

 knee-joint. The infrapatellar pad is the larger of the two, and 

 fills up the space between the lower end of the femur, the head of 

 the tibia, and the patella with its ligament. It adapts itself to the 

 different positions of the joint, and the ligamentum mucosum acts 

 as its regulator. The suprapatellar pad is situated around the 

 suprapatellar bursa and the pouch which the synovial membrane 

 sends upwards above the patellar surface of the femur. 



