SACRUM

The posterior bone of the pelvis, articulated to the last lumbar vertebra, and firmly united on each side to the hip bones; below, the os coccygis is attached to it. It probably derives its name from having been offered by the ancients in sacrifices. In young subjects it is composed of five or six pieces united by cartilages, but in more advanced age it becomes oi\p bone. [s. 1087]