The upper margin of the true pelvis is often called the brim, or inlet, of the pelvis. This is heart-shaped in the male and oval in the female owing to the shape of the upper part of the sacrum, which in the male is more prominent.

The angle formed by the bodies of the two pubic bones at the symphysis-i.e., the pubic arch - is a right angle in the female and an acute angle in the male. The ischial spines are turned inwards in the male and project straight from the ischium in the female.

Coccyx

The coccyx is turned forwards in the male and as a rule firmly joined to the sacrum. In the female it is straighter and has a movable joint.

From these differences it will be seen that the true pelvis is altogether more roomy in the female and the outlet wider, which is necessary for the purposes of childbirth.