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These air sacs open up or expand with each breath.

On careful dissection, around eight air sacs can be clearly seen.

In addition to their lungs, they have peripheral air sacs along each side.

Each was nearly two feet long, but full of cavities and air sacs.

These air sacs make up most of the lung tissue.

These large air sacs move less oxygen into the blood.

Facial air sacs under their skin help protect the impact with the water.

Evidence of air sacs has also been found in theropods.

Most birds have hollow main bones with air sacs in them.

In many areas, the delicate air sacs were torn, but that had happened long ago.