ARTICULATIONS OF TEE POSTERIOR LIMBS. 219 



ligaments. It is formed of two aponeurotic layers separated superiorly, but 

 confounded inferiorly. The superficial layer 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 envelops, like a cap, the femoral condyles. After becoming united, 

 these two laminse 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 

 popliteal vessels, and the 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 liga- 

 ment, as well as to the interarticular meniscii. 



c. 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. 141). 



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,\ongeY than the preceding, and oblique in the opposite dii-ection, 

 is inserted, inferiorly, into the little eminence 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. 



Sgnovial membranes. — For this articulation there are three synovial mem- 

 branes : a superior and two lateral. The first, very large and strengthened 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 lines, 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 metatareus. These 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 com- 

 municate with it. The three are separated from the ligaments of the patella by 

 a considerable mass of adipose tissue, which is prolonged into the inter-condyloid 

 notch, at the bottom of which it appeal's to be fixed. 



The synovial cavities sometimes communicate with each other, but, according 

 to Lesbre, this is rare. 



Movements— 'T\m imperfect hinge-joint can execute the two principal and 

 opposite movements of flexion and extension, and a somewhat limited accessory 

 movement of rotation. The mechanism of these movements being simple enough 

 to be readily understood without any preliminary explanation, they will not be 

 detailed here ; but some remarks will be made with regard to the displacement 

 the fibro-cartilages undergo, when the articulation is in motion. 



During flexion and extension, these bodies, fixed on the tibial facets, which 

 they transform into glenoid cavities, move with them on the condyles of the 

 femur, from before to behind, or behind to before, according to the movement 



