Medically Reviewed on April 24, 2013 by George Krucik, MD, MBA
Written and medically reviewed by the Healthline Editorial Team
Co-developed by:

In Depth: Bones and Lymphatics

The pelvis forms the base of the spine as well as the socket of the hip joint. The pelvic bones include the hip bones, sacrum, and coccyx.

The hip bones are composed of three sets of bones that fuse together as we grow older. Each set is nearly symmetrical across the body’s midline. The parts of the hip bone are:

  • Ilium: This is the largest part of the hip bone. The crests of the ilia are what people typically consider their hips as they typically can be felt at the waist.
  • Pubis: This is at the front of the hip bone closest to the genitals. There is a joint between the two pubes bones called the pubic symphasis. In women, this becomes more flexible in late pregnancy to allow the baby’s head to pass through during delivery.
  • Ischium: Below the ilium and next to the pubis, this circular bone creates the lowest portion of the hip bone. This is where the femur meets the pelvis to create the hip joint.

The sacrum is a triangular bone wedged into the rear section of the pelvis. It is made up of five fused vertebral bones. The female sacrum is shorter and wider than a male’s. The sacrum is connected to the tailbone, or coccyx, which is made of several fused vertebral bones at the base of the spine.

The female pelvic bones are typically larger and broader than a male’s. This is so a baby can pass through the pubic outlet, the circular hole in the middle of the pelvic bones, during childbirth. The pubic arch, or space under the base of the pelvis, is also wider for this reason. A man's pelvis is typically narrower and smaller than a woman's because they needed to be quick runners during man's hunter-gatherer period of history. 

The opening at the base of the pelvis, the obturator foramen, creates the ball-and-socket hip joint with the femur, the large bone of the leg. This joint and its ability to rotate in many angles is one of many pieces of anatomy that allows humans to walk.

The spine, or vertebral column, is a tower of bone that consists of 24 irregular-shaped bones along with the nine fused bones in the sacrum and coccyx. The spine gives human beings their posture as well as houses and protects the spinal column, the body’s major nerve center.

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