This consists of 5 ossified sacral vertebrae. The spinous processes are fused to the median sacral crest, the articular processes to the intermediate sacral crest and the transverse processes to the lateral sacral crest, respectively.
The ossification is complete only in adulthood. The original intervertebral discs never ossify or only when one reaches middle age.
The sacrum and the iliac bone of the pelvis together form a sacro-iliac joint on either side. The joint surfaces are very irregular.
The sacro-iliac joints have a weight-bearing and shock absorbing function in various directions.
