166 THM ASTICULATIONS.] 



internal synovial membrane. It is fixed by its inferior extremity to the 

 imprints wbicb cover the internal tibial tuberosity. 



Its fibres are disposed in two layers, which slightly intercross in X fashion ; 

 those passing downwards and forwards adhere to the border of the internal 

 meniscus. Covered by the aponeurosis of the adductor muscles of the leg, 

 this ligament adheres by its deep face to the internal meniscus. 



c. The posterior ligament belongs to the class of membranous or capsular 

 ligaments. It is formed of two aponeurotic laminae separated superiorly, 

 but confounded inferiorly. The superficial lamina is composed of strong, 

 fibrous, intercrossed fasciculi, perforated with vascular openings. It is fixed, 

 above, to the posterior face of the femur, below the external gastrocnemius 

 muscle. The deep lamina envelopes, like a cap, the femoral condyles. 

 After becoming united, these two laminae are attached to the posterior face 

 of the tibia, close to the superior articular face of that bone. Its external 

 face is in contact with the po^iteal vessels, and the external gastrocnemius 

 muscle. Its internal face is covered throughout nearly the whole of its extent 

 by the lateral synovial membranes, embraces the condyles of the femur, and 

 adheres to the posterior crucial ligament, as well as to the interarticular 

 meniscii. 



d. The interosseous ligaments are two funicular bands lodged in the inter- 

 condyloid notch. They are more commonly designated crucial ligaments, 

 because they cross each other at their middle part, like the letter X. 

 (Fig. 91.) 



The anterior, oblique downwards and forwards, is attached by its superior 

 extremity to the bottom of the intercondyloid notch, and inwardly to the 

 external condyle. Its inferior extremity is fixed in the groove on the summit 

 of the tibial spine. The fibres entering into its formation are not parallel, 

 but slightly twisted in a spiral manner. 



The posterior, longer than the preceding, and oblique in the opposite 

 direction, is inserted, inferiorly, into the little emiQonce behind the internal 

 tibial facet ; whence it goes to the bottom of the intercondyloid notch, to be 

 attached by its superior extremity within the internal condyle. 



Synovial memhranes. — For this articulation there are three synovial 

 membranes : a superior and two lateral. The first, very large and sustained 

 by the femoro-patellar capsule, facilitates the gliding of the patella on the 

 femoral pulley; it is prolonged in a cul-de-sac below the insertion of the 

 crural triceps. The other two, which lubricate the articular surfaces of the 

 proper femoro-tibial joint, include the crucial ligaments between them, and 

 cover the posterior ligament, the lateral ligaments, and the fibrous fasciculi 

 for the attachment of the meniscii. The external covers, in addition, the 

 tendon of the popliteus muscle, and furnishes a vast cul-de-sac which descends 

 in the anterior groove of the tibia to envelop the tendon common to the 

 anterior extensor of the phalanges and the flexor of the metatarsus. Those 

 two femoro-tibial synovial membranes lie against that of the femoro-patellar 

 articulation, in front of the condyles and the notch which separates them, 

 and if not always, at least not unfrequently. they communicate with it. The 

 three are separated from the ligaments of the patella by a considerable mass 

 of adipose tissue which is prolonged into the intercondyloid notch, at the 

 bottom of which it appears to be fixed. 



Movements.— This imperfect hinge joint can execute the two principal and 

 opposite movements oi flexion and extension, and a somewhat limited acces- 

 sory movement of rotation. The mechanism of these movements being 

 simple enough to be readily understood vdthout any preliminary explanation, 



