- The sacrum and coccyx are part of the spine and are located in the pelvis.
- The sacrum articulates with:
- the fifth lumbar vertebra superiorly, forming the lumbosacral joint.
- the ilium of the pelvic bone laterally, forming the sacroiliac joint.
- the coccyx inferiorly, forming the sacrococcygeal joint.
NOTES:
- The sacrum is composed of five vertebral elements (S1-S5) that do not fully form and that fuse into one bone.
- The sacrum is an upside-down triangle, with the base of the sacrum at the top (superior end) and the apex of the sacrum at the bottom (inferior end).
- The coccyx is usually said to be composed of two-four vertebral elements that do not fully form.
- The coccyx does not ossify until later in adulthood.
- The coccyx is considered to be the evolutionary remnant of a tail.
- The pelvis is a transitional body part. It has both axial body bones (sacrum and coccyx) and appendicular body bones (pelvic bones) within it.
![Posterior view of the sacrum and coccyx.](https://learnmuscles.com/wp-content/uploads/2017/05/14-Sacrum-posterior-0907-modified-931x1024.jpg)
Posterior view of the sacrum and coccyx.
![Anterior view of the sacrum and coccyx.](https://learnmuscles.com/wp-content/uploads/2017/05/14-Sacrum-anterior-1760-1024x1024.jpg)
Anterior view of the sacrum and coccyx.
![Right lateral view of the sacrum and coccyx.](https://learnmuscles.com/wp-content/uploads/2017/05/14-Sacrum-lateral-0865-647x1024.jpg)
Right lateral view of the sacrum and coccyx.
![Superior view of the upper surface of the sacrum.](https://learnmuscles.com/wp-content/uploads/2017/05/14-Sacrum-sacral-canal-1781-1024x560.jpg)
Superior view of the upper surface of the sacrum.