# What is the diaphragm (in breathing)?

The the diaphragm is called the diaphragm. Gray's Anatomy (1918) describes it as a dome-shaped sheet of muscle and tendon.

## What it means

- A dome-shaped sheet of muscle and tendon.
- The principal muscle of breathing.
- When it contracts and flattens, air is drawn into the lungs.

## Action steps

1. Between the chest cavity and the abdominal cavity.
2. Attached to the lower ribs, sternum, and lumbar vertebrae.
3. Pierced by the esophagus, aorta, and inferior vena cava.

## Sources

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

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