260 



ARTICULATION OF THE KNEE. 



thick at their external, and very thin at their internal edges ; so 

 tiiat iliey form two superficial concavities on the top of the 

 tibia. 



Their extremities are attached by ligaments to the central 

 protuberance of the tibia, and their anterior extremities are also 

 connected by a ligament to each other. 



The synovial membrane is so reflected as to cover the whole 

 Fig. 64.* surface of these cartilages, except the 



exterior edge, which is connected with the 

 external ligaments of the articulation. 



The use of these cartilages, is evidently 

 to form concavities on the top of the tibia, 

 for accommodating the condyles of the os 

 femoris ; and upon examination, they 

 will not appear so anomalous as they do 

 at first view, for there is a considerable 

 analogy between them and the cartilagi- 

 nous edges of the glenoid cavity and of the 

 acetabulum. These are called the semi- 

 lunar curtilages. The internal is but little 

 more than a semicircle ; the external is nearly circular in its 

 shape. 



The patella appears to project into the cavity of the joint, 



* A longitudinal section of the left knee joint, showing 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 liga- 

 inentum patellae. 5. The cancellous structure of the head of the tibia. 6. A 

 bursa situated between the ligamentum patellse 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 saculus (at 8), along the inner sur- 

 face of the patella; then over the adipose mass (7) 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. 



