SACRUM
From NeuroRehab.wiki
SUMMARY
1. Five sacral vertebrae & costal elements fuse to form this bone.
2. It articulates with the ilum: but the SI joint is not weight bearing. The ligaments attached to it bear the weight of the body.
3. The upper surface of S1 slopes 30o or more.
Image: Case courtesy of OpenStax College, Radiopaedia.org. From the case rID: 42764.
Reference(s)
R.M.H McMinn (1998). Last’s anatomy: regional and applied. Edinburgh: Churchill Livingstone. Get it on Amazon.
Drake, Richard L., et al. Gray's Anatomy for Students. Elsevier, 2023. Get it on Amazon.