Choana

The choanae (sg.: choana), posterior nasal apertures or internal nostrils are two openings found at the back of the nasal passage between the nasal cavity and the pharynx, in humans and other mammals (as well as crocodilians and most skinks). They are considered one of the most important synapomorphies of tetrapodomorphs, that allowed the passage from water to land.

In animals with secondary palates, they allow breathing when the mouth is closed. In tetrapods without secondary palates their function relates primarily to olfaction (sense of smell).

The choanae are separated in two by the vomer.