ocr: RESPIRATION Respiratory System HEN A HUMAN breathes, TRACHEA Wineh lungs expand as air flows in, and deflate as it flows out. In a bird, the air bypasses the lungs, moving first into the FORWARD - - FORWARD air lungs. sacs, which unique work like one-way bellows AIRS - ER AIR SACS to push the air through the - - - This flow - of air means that the lungs are always in contact with fresh, LUNG LUNG oxygenated air. REAR REAR AIR SACS AIR: SACS How BIRDS BREATHE
