18 



as this passes out of the pelvis. These fibres are not present in the 

 same well-developed form in the male. 



The role which this ligamentous band plays in the movements 

 that take place at the joint in women, and consequently in the produc- 

 tion of the sulcus praeauricularis cannot be too strongly insisted upon. 

 For owing to the more horizontal position of the sacrum in women, 

 the weight of the trunk tends to depress the base with a coincident 



Fig. 4. Pelvis of a woman. The arrow shows position of the longitudinal fibres 

 of the ventral sacro-iliac ligament. 



lifting of the posterior end of the bone. It is this movement which 

 the longitudinal fibres are adapted to check. 



The articular surfaces of the sacrum and ilium are smaller in 

 women than in men and they are also much less closely adapted the 

 one to the other. In men the shape of the surfaces is such that in 

 most cases they firmly interlock and any movement between the bones 

 is well-nigh impossible. In women on the contrary, the sacral articular 

 surface is grooved throughout its long axis, while the similar surface 

 on the ilium is raised along its whole length, the two surfaces forming 

 thus a sort of condylarthrosis which permits of a certain amount of 

 gliding antero-posteriorly, and also of a slight rotation of each hip bone 



