sacrum sa·crum (sā'krəm, sāk'rəm)
n. pl. sa·cra (sā'krə, sāk'rə)
The triangular segment of the spinal column that forms part of the pelvis and closes in the pelvic girdle posteriorly, is formed between the ages of 16 and 25 by the fusion of five originally separate sacral vertebrae, and articulates with the last lumbar vertebra, the coccyx, and the hipbone on either side.
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