The area of the body bounded by the pelvic bones and including the reproductive organs, bladder and rectum. It is easiest to think of this as the lower part of the abdominal cavity. As a pregnancy progresses the uterus rises up out of the pelvic cavity and into the upper part of the abdominal cavity. As the baby prepares to pass through the birth canal, the head or presenting part of the baby drops into the pelvic cavity. This is sometimes called 'lightening' and results in a physical change in the outward appearance of the abdomen.