512 THE CURVATURES OF THE ARTICULAR SURFACES, AND 



handed screw combination in the right, a left-handed in the 

 left hip. 



The ligamentum teres. When the posterior area is 

 screwed home, the round ligament is quite slack and folded 

 over on itself forwards ; the posterior angle of its femoral 

 attachment having revolved over and in front of its anterior, 

 while the posteriqr area is screwing off, that is, performing the 

 first half of flexion, by screwing and rolling backwards, down- 

 wards, and onwards, the ligamentum teres gradually tightens, 

 so that when the shaft of the thigh bone has passed so far 

 forwards and inwards as it is when the foot comes in contact 

 with the ground in the step, when the trunk has inclined 

 slightly forward to the same side over the head of the thigh 

 bone, it becomes quite tight, flattened out, and lodged in the 

 cartilaginous fossa below the femoral pit, and bounded on each 

 side by the screwed anterior and posterior borders of that 

 groove. The joint is now in mid flexion (or mid extension), 

 that is, the posterior femoral area, and the corresponding 

 cotyloid area are about to break contact, and the anterior 

 femoral and corresponding area to come into action. When 

 this takes place the ligamentum teres again gradually 

 slackens, folding backwards with its anterior angle of femoral 

 attachment revolving over the posterior. In extreme flexion 

 when the lower part of the posterior area of the head of the 

 femur passes across the non-cartilaginous fossa of the acetabu- 

 lum and rests on the pubic area, a position which can only be 

 assumed along with extreme abduction, the ligamentum teres 

 folds still further backwards and inwards. As the hip joint 

 is essentially a hinge joint, the ligamentum teres represents 

 the internal lateral ligament, as the capsular is a modified 

 external lateral ligament. The fossa for the femoral 

 attachment of the ligamentum teres lies in the line of oscu- 

 lation of its two areas ; and, therefore, like the internal lateral 

 ligament of the hock-joint in the horse, becomes tense at mid 



