CAVITY OF THE PELVIS. 171 



The outlet or lower opening of the pelvis is also larger in 

 women. 



This greater size of the pelvis and its openings, in women, is 

 derived particularly from the following circumstances : 



The os sacrum is broader, and sometimes straighter than in 

 men. 



The ossa ilia are flatter, and consequently the ossa ischia are 

 farther apart. 



The ligamentous cartilage at the symphysis pubis is broader, 

 and shorter. 



The angle formed by the crura of the ossa pubis with each 

 other, at the symphysis, is much larger. 



The pelvis, considered as a whole, is very irregular, though 

 symmetrical in its shape. It has the form of a truncated cone, 

 or a funnel with its base upwards, curved from behind forward 

 with its concavity in front, and is bounded both above and 

 below by bony walls of unequal elevation. It is divided by the 

 projection of the base of the sacrum and the two ilio-pectineal 

 lines, into a greater and lesser pelvis, the former of which is 

 above. The dividing line is called the superior strait of the 

 lesser pelvis. The bony walls of the greater pelvis is incom- 

 plete. The boundaries of this cavity, are formed upon the 

 sides by the iliac fossa?, and behind by a notch which is nearly 

 filled up, when the last lumbar vertebrae is left connected with 

 the sacrum ;* and in front by all the wide triangular opening be- 

 tween the anterior superior spine of the ^lium of each side and 

 the symphysis pubis'which is filled up by the lower part of the 

 abdominal muscles. From the flaring direction of the upper 

 part of the ilia, the diameters of the base of this cavity, or that 

 towards the abdomen, is greater than those opposite the ilio- 

 pectineal lines. 



The lesser pelvis, forms nearly an entire bony canal, and 

 which the student is too apt to consider as constituting the whole 

 pelvis. This cavity is larger at its middle than at its extremities. 

 It is bounded behind by the sacrum and coccyx ; in front by the 



* The attachment of the lumbar muscles completes this wall behind. 



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