alligators, much like birds, have been shown to exhibit unidirectional movement of air through their lungs. most other amniotes are believed to exhibit bidirectional, or tidal breathing. for a tidal breathing animal, such as a mammal, air flows into and out of the lungs through branching bronchi which terminate in small dead-end chambers called alveoli. as the alveoli represent dead-ends to flow, the inspired air must move back out the same way it came in. in contrast, air in alligator lungs makes a circuit, moving in only one direction through the parabronchi. the air first enters the outer branch, moves through the parabronchi, and exits the lung through the inner branch. oxygen exchange takes place in extensive vasculature around the parabronchi.