The pelvic canal

The roughly circular space enclosed by the pubic bones at the front, and the ischium on either side at the back, is called the pelvic canal -- the bony passage through which the baby must pass. This canal has a curved shape because of the difference in size between the anterior (front) and posterior (back) borders of the space created by the pelvic bones. You can see it from the side view in the figure below.