This image shows the human sacrum, which is composed of  five fused sacral vertebrae (S1-S5).  The sacrum shapes, strengthens and stabilizes  the pelvis.  It articulates superiorly with the last lumbar vertebra (L5) and inferiorly with the coccyx (not shown), which is composed of several fused caudal vertebrae and laterally with the coxal (innominate) bone.