It's the same thing as a hollow bone. That's one of the characteristics birds posse than enables them to fly (if their bones had the same weight as ours, they wouldn't be able to lift). Some dinosaurs had the same type of bones.
Hope it helped.
Pneumatics is the branch of physics or technology concerned with the mechanical properties of gases. And that's what "Pneumatics" mean
The development of air cells or cavities, such as those of the mastoid and ethmoidal bones.
It is extremely essential in Hydraulics and mechanics. Your car would not run without pneumatics.