In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation.

With extreme damage to the septum and columella, the two nostrils are no longer separated and form a single larger external opening.

Like other tetrapods, humans have two external nostrils (anterior nares) and two additional nostrils at the back of the nasal cavity, inside the head (posterior nares, posterior nasal apertures or choanae).

[1] Each external nostril contains approximately 1,000 strands of nasal hair, which function to filter foreign particles such as pollen and dust.

Widely-spaced nostrils, like those of the hammerhead shark, may be useful in determining the direction of an odour's source.