Avian Lung Structure Win When a bird inhales, air flows past the lungs directly into the poster nor nir sacs Ante air 5acs Windon Anterior air sacs Posterior air sacs When the bird exhales. air flows from the postenor air sacs forward into the lung Air then Rows into the antenor air sacs in front of the lungs when the bird inhales The air then passes out of the body ith the next exhalation8