# What is the sacrum?

It is called the sacrum. Gray's Anatomy (1918) describes it as a large, triangular bone made from the fusion of five sacral vertebrae.

## What it means

- A large, triangular bone made from the fusion of five sacral vertebrae.
- Forms the back wall of the pelvis.
- Transmits the weight of the upper body to the hip bones.

## Action steps

1. Between the two hip bones.
2. Below the lumbar spine and above the coccyx.
3. Joins each hip bone at the sacroiliac joint.

## Sources

- [Gray's Anatomy of the Human Body (1918)](https://www.bartleby.com/107/)

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