triangular bone at base of spine that forms by fusing of sacral vertebrae (S1–S5) between ages 18 and 30, situated at upper, back part of pelvic cavity, between two wings of pelvis
Joe Williams, John Carlson, Damon Hernandez, Don Brutzman
X3D-Edit 4.0, https://www.web3d.org/x3d/tools/X3D-Edit
X3D Tidy, https://www.web3d.org/x3d/stylesheets/X3dTidy.html