ANATOMY OF THE KNEE-JOINT. 223 



of the knee, the biceps and semimembranosus, only act in- 

 directly as rotators, through the medium of the articular 

 surfaces and ligaments. I conceive, however, that the 

 latter may act directly in producing rotation inwards at the 

 commencement of flexion ; for its tendon, instead of being 

 inserted, as is usually stated, into the back part of the inner 

 tibial condyle, passes forwards and outwards round the head 

 of the bone in a distinct groove, in which it moves, being kept 

 in its place by prolongations of the internal lateral ligaments 

 of the joint, and thus presenting the same general mode of 

 insertion as the three muscles already alluded to. 



The rotation outwards, at the completion of extension, is 

 produced indirectly by the quadriceps-extensor ; the form of 

 the articular surfaces, and the tightening of the external 

 crucial ligament, co-operating with the group of extensor 

 muscles. 



Meyer has detected a very beautiful adaptation of parts in 

 connection with this latter movement, and has thus explained 

 the characteristic enlargement, and the extensive attachment 

 to the patella, of the vastus internus muscle. When the knee 

 is extended, the ligamentum patellse, instead of being perpen- 

 dicular, will be found to pass downwards and outwards to its 

 tibial attachment, which has moved outwards in the rotation 

 of the leg. The lower portion of the vastus internus is en- 

 larged, and the upper portion of its tendon is attached to the 

 greater part of the inner edge of the patella, for the purpose 

 of preventing that bone from being pressed against the outer 

 part of the femoral trochlea during the rotation outwards of 

 the leg, by drawing it inwards and upwards, and keeping its 

 axis in the line of the ligamentum patellae ; while the lower 

 portion of its tendon passes down to be attached somewhat 

 obliquely to the inner side of the head of the tibia, and thus 

 assists directly in rotating the leg outwards. 



Meyer has also shown that, in standing quietly upright 



