226 ANATOMY OF THE KNEE-JOINT. 



external facets leave the femoral trochlea and become sheathed, 

 and the space occupied partly by the supra-patellar, but 

 principally by the supra-trochlear pads. The middle internal 

 and external patellar facets now come in contact with the 

 middle portions respectively of the inner and outer halves of 

 the femoral trochlea ; while the internal perpendicular and 

 the two inferior facets are sheathed and padded as before. 



In the fourth or last stage of extension, the middle internal 

 and external facets also recede from the surface of the trochlea, 

 and along with the internal longitudinal already sheathed, 

 become applied against the fore part of the femur above its 

 articular surface, the intervening space being stuffed by the 

 supra-patellar, supra-trochlear, and upper pads, in the ascending 

 cul-de-sac of the synovial membrane. In this last stage, 

 the only portions of the patella in contact with the cartilaginous 

 surface of the femur, are the inferior internal and external 

 facets, or the latter, if one only exists. These slip somewhat 

 abruptly upwards and inwards upon a narrow ledge or furrow, 

 which terminates the femoral trochlea above, and forms a 

 resting-place for the inferior facets of the patella in the 

 complete extension of the joint. 



Attention should be directed to the fact, that the patella, 

 in complete flexion, lies so much to the outer side of the 

 joint as to leave the inner condyle, with the exception of 

 the crescentic facet, exposed in front. Meyer has pointed 

 out that the external position assumed by the patella in 

 complete flexion depends on the external patellar retina- 

 culum, which consists of two oblique bands, extending from 

 the outer edge of the bone to the anterior margin of the 

 ileo-tibial band of the fascia lata already alluded to ; and 

 which, as it slips backward during flexion, drags the patella 

 by means of the external retinaculum outwards. 



In complete extension, again, the patella lies at the inner 

 iiide of the upper end of the joint, with its long axis directed 



