A
nostril (or
naris , plural
nares ) is one of the two channels of the
nose, from the point where they bifurcate to the external opening. 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.
Fish do not breathe through their noses, but they do have two small holes used for
smelling, which may, indeed, be called nostrils.