SACRAL VERTEBRAE

Fusion of the three segments that constitute the sacrum may not be completed until 18 months after birth; fusion involves both the vertebrae and the ossified inter­vertebral disks. The sacrum is deeply embedded between the wings of the ilia so that only the spinous processes (sacral crest) are palpable through the skin; however, its caudoventral part and the first few (or more) caudal vertebrae can be palpated digitally per rectum. The first sacral vertebra forms a rigid joint with the wing of the ilium.