510 THE CURVATURES OF THE ARTICULAR SURFACES, AND 



position, that is when standing on both feet, the hip-join|; 

 being in full extension, the posterior area of the head of the 

 femur is in close contact and congruent M'ith the ischial area 

 of the acetabulum, the undulation outwards of the posterior 

 margin of the articular surface of the head of the femur 

 occupying the broadest part of the ischial surface of the 

 acetabulum ; while the undulation inwards of its upper part 

 occupies the notch in the margin of the acetabulum, between 

 the ischial and iliac portions of the cavity. 



In semi-flexion of the hip-joint, the anterior area of the 

 head of the femur is congruent with the iliac area, this 

 broadest or projecting portion occupying the undulation of 

 the former, which extends outwards on the front of the neck 

 of the bone ; while the inward undulations on each side of it 

 occupy respectively the acetabular notches between the 

 ischial and iliac, and between the iliac and pubic portions 

 of the cavity. 



The anterior border of the femoral pit is the thread of this 

 screwed area, and curves more rapidly as it approaches the 

 posterior angle of the attachment of the lig-teres. The area 

 itself is the rolling surface. It is a right-handed screw in the 

 right hip, a left in the left. It therefore screws the head of 

 the thigh bone out of the socket in flexion, but screws it 

 against the iliac area, advancing its superior external angle or 

 apex against the outer or projecting marginal portion of that 

 area. During the action of this area the ilio-femoral ligament 

 is slack ; when completed the pubic and ischial portions of the 

 capsule become tense and act as the tightening arrangements 

 of the combination. 



In complete flexion the lower portion of the posterior 

 area of the head of the femur, which occupies the cotyloid 

 fossa during semi-flexion, is applied and rests upon the pubic 

 area ; the posterior undulation outwards on the femur which 

 occupies the ischial projection in full extension, now occupies 



