218 



SPECIAL ANATOMY OF THE SKELETON 



Axes of the Pelvis (Fig. 172). The plane of the inlet of the true pelvis will 

 be represented by a line drawn from the base of the sacrum to the upper margin 

 of the symphysis pubis. A line carried at right angles with this at its middle 

 would correspond at one extremity with the umbilicus, and at the other with the 

 middle of the coccyx; the axis of the inlet is therefore directed downward and 

 backward. The axis of the outlet, prolonged upward, would touch the base of 



the sacrum, and is therefore directed downward 

 and forward. The axis of the cavity is curved 

 like the cavity itself; this curve corresponds to 

 the concavity of the sacrum and coccyx, the 

 extremities being indicated by the central points 

 of the inlet and outlet. A knowledge of the 

 direction of these axes serves to explain the 

 course of the fetus in the passage through the 

 pelvis during parturition. 



Differences between the Male and Female 

 Pelvis. The female pelvis, looked at as a whole, 

 is distinguished from the male by the bones 

 being more delicate, by its width being greater 

 and its depth smaller. The whole pelvis is less 

 massive, and its bones are lighter and more 

 slender, and its muscular impressions are slightly 

 marked. The iliac fossae are shallow, and the 

 anterior iliac spines widely separated; hence the 

 greater prominence of the hips. The inlet in 

 the female is larger than in the male; it is more 

 nearly circular, and the sacrovertebral angle 



projects less forward. The cavity is shallower and wider; the sacrum is shorter, 

 wider, and less curved; the obturator foramina are triangular, and smaller in size 

 than in the male. The outlet is larger and the coccyx more movable. The 



Plane o. 



FIG. 172. Vertical section of the pelvis, 

 with lines indicating the axis of the pelvis. 



FIG. 173. Diameters of the pelvic inlet in the female. 



spines of the ischia project less inward. The tuberosities of the ischia and the 

 acetabula are wider apart. The pubic arch is wider and more rounded than in 

 the male, where it is an angle rather than an arch. In consequence of this the 



