Question

Birds have a flow-through respiratory system in which air flows unidirectionally from the posterior sacs into the lungs, then into these?

Answer 1

anterior air sacs

Figure 39.14  a  Birds have a flow-through respiratory system in which air flows unidirectionally from the posterior sacs into the lungs, then into the anterior air sacs. The air sacs connect to openings in hollow bones.  b  Dinosaurs, from which birds descended, have similar hollow bones and are believed to have had a similar respiratory system.  credit b: modification of work by Zina Deretsky, National Science Foundation .