Final answer:
The Eustachian tube connects the middle ear to the outer ear and equalizes the pressure there with the outside atmosphere.
Step-by-step explanation:
The Eustachian tube connects the middle ear to the outer ear. It is responsible for equalizing the pressure in the middle ear with the outside atmosphere. When we swallow or yawn, the Eustachian tube opens to allow air to flow into or out of the middle ear, helping to maintain equal pressure.