THE GENERAL MECHANISM OF THE HUMAN HIP-JOINT. 511 



the pubic projection, and the pubic notch is occupied by the 

 posterior inferior inward undulation. 



In complete extension, as in standing erect on both feet, 

 the posterior area of the head of the femur is congruent with 

 the ischial area of the acetabulum, and with the superior 

 internal portion of the iliac area ; being screwed backwards, 

 upwards, inwards, and forwards, by the action of the extensor 

 muscles of the hip, and by the tightening of the successive 

 fasciculi of, and ultimate tension of, the entire ilio-femoral 

 portion of the capsule. During extension, the thigh passes 

 backwards and outwards, rotating outwards at the same time. 

 It is, to use the current nomenclature, a combination of ex- 

 tension, abduction, and rotation outwards. These movements 

 are the necessary accompaniments of the movements already 

 described between the posterior femoral, and ischial articular 

 areas. The movements of these two areas in extension are 

 such that the male or femoral area advances by a combination 

 of rolling and gliding along the female or ischial, apex towards 

 apex, and base towards base, until the opposite convex and 

 concave surfaces become congruent throughout, and the joint 

 is screwed home in extension. If a portion of the inner wall 

 of the acetabulum be removed, so as to display the respective 

 movements of the areas under consideration, the most pro- 

 minent portion of the femoral area will be observed to 

 advance inwards and forwards, as it advances laterally along 

 its action of rotation. The head of the femur is thus, during 

 extension, screwed, and therefore forced into the acetabulum ; 

 from without inwards, and from behind forwards. The 

 posterior border of the femoral pit constitutes the proper 

 thread of this screwed area ; its superior more rapidly curved 

 portions at the posterior extremity of the attachment of the 

 lig.-teres advancing during the movement forward and inward. 

 The area itself constitutes the rolling surface. This area, with 

 the ischial and deeper portion of the iliac, constitutes a right- 



