224 ANATOMY OF THE KNEE-JOINT. 



on one or both limbs, the knees are not necessarily kept 

 straight by continued action of the extensor muscles, for the 

 ligaments of the patella may be slack. The continued 

 extension cannot be the effect of the superincumbent pressure 

 of the body, for the transverse plane, in which the common 

 centre of gravity is situated, lies behind the transverse axes 

 of the knee-joints. Two arrangements conduce to this re- 

 markable example of economy in muscular action. When the 

 foot is on the ground, and the knee extended, the inward 

 rotation of the leg in the commencement of .flexion cannot 

 take place ; and if the pelvis and trunk are kept erect, the 

 reverse rotation of the thigh-bone outwards is prevented by 

 the tightened condition of the ileo-femoral band of the hip- 

 joint : but if the trunk and pelvis be inclined forwards, 

 although the ileo-femoral band is relaxed, and the femur 

 relieved, the tendency to flexion of the knee-joint is removed 

 by the passage of the line of gravity to the front of the 

 transverse axis of the articulation. The thick longitudinal 

 band of the fascia lata on the outer side of the thigh, ex- 

 tending from the anterior superior spinous process of the 

 ileum, and from the inferior attachment of the tensor vagina 

 femoris to the fore part of the outer condyle of the tibia 

 (ligamentum ileotibiale), is another arrangement for econo- 

 mising muscular exertion ; for as long as the pelvis is kept 

 erect on the heads of the thigh-bones by the glutei maximi 

 muscles, it is evident that these ileo-tibial bands must tend to 

 keep the knees extended, and transfer the action of the 

 quadriceps-extensor to the great muscle of the hip. 



The patella exhibits various interesting relations during 

 the movements of the joint ; and in addition to those observed 

 by Meyer, others hitherto unrecorded may be pointed out. 

 Meyer states that the under half of the patella is in contact 

 with the femoral trochlea in extension, and the upper half in 

 flexion ; but if the bone is carefully examined, the following 



