Figure 4: Schematic of avian respiration. (A) During inspiration, air in the trachea flows to the caudal air sacs (caudal thoracic and abdominal air sacs) while air in the lungs flows to the cranial air sacs (cranial thoracic and clavicular air sacs). (B) During expiration, the air in the caudal air sacs flows towards the lungs while the air in the cranial airs sacs flows out the trachea. Credit: König et al.