| os sacrum | <anatomy> The triangular-shaped bone lying between the 5th lumbar vertebra and the coccyx (tailbone). It consists of 5 vertebrae fused together and it articulates on each side with the bones of the pelvis (ilium), forming the sacroiliac joints. (17 Dec 1997) |
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| transverse lines of sacrum | One of four ridges that cross the pelvic surface of the sacrum; these mark the positions of the intervertebral disks between the bodies of the five sacral vertebrae in the immature bone. Synonym: lineae transversa ossi sacri. (05 Mar 2000) |
| lateral part of sacrum | The lateral mass of the sacrum formed by the fused costal elements. Synonym: pars lateralis ossis sacri. (05 Mar 2000) |