Sacro

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The sacrum is a shield-shaped bony structure located at the base of the lumbar vertebrae. It connects to the pelvis, forms the posterior pelvic wall and strengthens and stabilizes the pelvis. On the same end as the sacrum, there are 2 to 4 small and partially fused vertebrae called the coccyx or "tailbone" that provides a slight support for the pelvic organs, but is actually a bone of little use.