Concept
Version 7
Created by Boundless
Types of Breathing
Avian respiratory system
(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.
Source
Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:
"OpenStax College, Breathing. October 17, 2013."
http://cnx.org/content/m44797/latest/Figure_39_03_01ab.jpg
OpenStax CNX
CC BY 3.0.