The sacrum is the bone of the spinal column toward the caudal end right below the seventh lumbar vertebrae and directly above the coccyx. It is triangular in shape and comprised of five bones that are fused together.
The sacrum consists of 5 verterbrae that start out as separate bones at birth and fuse by adulthood into one bone. It is at the lower portion of the vertebral column, below the lumbar vertebrae.