KNEE JOINT. 



151 



Fig. 72.* 



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 surfaces of the con- 

 dyles of the femur, of the head of 

 tibia, and of the inner surface of 

 the patella ; it covers both surfaces 

 of the semilunar fibro-cartilages, and 

 is reflected upon the crucial liga- 

 ments, and upon the inner surface 

 of the ligaments which form the cir- 

 cumference of the joint. On each 

 side of the patella, it lines the ten- 

 dinous aponeuroses of the vastus in- 

 ternus 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. 



Between 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 con- 

 dyles. 



* A longitudinal section of the left knee joint, shewing the reflections of its 

 synovial membrane. 1. The cancellous structure of the lower part of the 

 femur. 2. The tendon of the extensor muscles of the leg. 3. The patella. 

 4. The ligamentum patellfe. 5. The cancellous structure of the head of the 

 tibia. 6. A bursa situated between the ligamentum patellae and the head of 

 the tibia. 7. The mass of fat projecting into the cavity of the joint below the 

 patella. * * The synovial membrane. 8. The pouch of synovial membrane 

 which ascends between the tendon of the extensor muscles of the leg, and 

 the front of the lower extremity of the femur. 9- One of the alar ligaments ; 

 the other has been removed with the opposite section. 10. The ligamentum 

 mucosum left entire; the section being made to its inner side. 11. The 

 anterior or external crucial ligament. 12. The posterior ligament. The 

 scheme of the synovial membrane, which is here presented to the student, 

 is divested of all unnecessary complications. It may be traced from the 

 sacculus (at 8), along the inner surface of the patella; then over the adipose 

 mass (~) from which it throws off the mucous ligament (10) ; then over the 

 head of the tibia, forming a sheath to the crucial ligaments ; then upwards 

 along the posterior ligament and condyles of the femur, to the sacculus whence 

 its examination commenced. 



