EMBRYOLOGY

		The final set of models, arranged in this photograph in progressively more mature developmental stages beginning from the bottom left, represents the following stages of development identified in the following stained microscope slides of lung tissue:
		the pseudoglandular stage ((contains very few potential passages (bronchi) and few terminal acini (future breathing chambers)),
		the cannalicular stage (the lung grows by proliferating multiple generations of bronchi and the acini bud from the tips of the branches),
		into classic pneumatic structures, the terminal sac stage.
		Post-natal lungs are composed primarily of airways whose elastic walls are supported under differential pressure by a complex geometrically structured anatomy.