- a sac containing air.
- alveolus(def 2).
- any of certain cavities in a bird’s body connected with the lungs.
- a saclike dilation of the wall of a trachea in many insects.
- any of the membranous air-filled extensions of the lungs of birds, which increase the efficiency of gaseous exchange in the lungs
- any of the thin-walled extensions of the tracheae of insects having a similar function
- A tiny, thin-walled, capillary-rich sac in the lungs where the exchange of oxygen and carbon dioxide takes place.alveolar sac
- An air-filled space in the body of a bird that forms a connection between the lungs and bone cavities and aids in breathing and temperature regulation.
- See alveolus.
- A saclike enlargement in the trachea of an insect.
- A baglike piece of skin or tissue below the jaw of certain animals, such as the bullfrog and orangutan, that can be inflated to increase sound production.