172 DIMENSIONS OF THE PELVIS. 



symphysis pubis and a part of the obturator foramen ; and upon 

 the sides, by the bony surface which corresponds to the cotyloid 

 cavity. Its superior margin (superior strait,) is regular and 

 ovoidal in its shape. Its longest diameter is transverse. Its 

 inferior strait is very irregular, though symmetrical in the form 

 of its bony walls ; and in consequence of the posterior walls of 

 this pelvis being of much greater length than the anterior, 

 presents an oblique cut, which faces slightly forwards, 

 so that if its axis was extended downwards, it would 

 cross just above the middle of the thigh. It is bounded 

 behind, by the point of the coccyx ; in front, by the sym- 

 physis pubis ; and on the side, by the tuberosities of the 

 ischium. The sacro-sciatic notches and the arch of the pubis, 

 are filled up by ligaments and soft parts. From the general 

 form of the whole pelvic cavity it will then be obvious, that a 

 body passing through its axis from above downwards, must 

 advance successively in three directions : 1st, as it passes 

 through the greater pelvis, obliquely backwards ; 2d, vertically ; 

 and 3d, as it passes through the inferior strait, obliquely 

 forwards. 



For obstetrical purposes, it is necessary for the student to 

 have precise notions in regard to the dimensions of the pelvis. 

 To determine this, it is necessary to measure the superior 

 opening of the greater pelvis, and the two straits of the 

 lesser. 



The pelvis of the male, differs in many respects from that of 

 the female. In the former length predominates, in the latter, 

 breadth. In the female all the diameters of the pelvis are more 

 extensive than those of the male, which is caused by the greater 

 size and outward direction of the iliac fossae, from a less degree 

 of curvature in the iliac crests, and from the roundness of the 

 pubic arch which in the male forms an acute angle. In conse- 

 quence of the wider space which exists between -the cotyloid 

 cavities, the gait of the female is characterized by more lateral 

 rotation or waddling, than that of man. A 



In a well formed woman, the different measurements are 

 nearly as follows : 



