A nostril (or naris , plural ''nares'' ) is either of the two
orifices
A body orifice is any opening in the body of an animal.
External
In a typical mammalian body such as the human body, the external body orifices are:
* The nostrils, for breathing and the associated sense of smell
* The mouth, for eating, bre ...
of the
nose. They enable the entry and exit of air and other gasses through the
nasal cavities. In
birds and
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s, 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 noses, but they do have two (but
cyclostomes have merged into one) small holes used for
smelling
The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste.
In humans, it ...
, which can also be referred to as nostrils.
In
humans, the
nasal cycle is the normal
ultradian cycle of each nostril's blood vessels becoming engorged in swelling, then shrinking.
The nostrils are separated by the
septum
In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate.
Examples
Human anatomy
* Interatri ...
. The septum can sometimes be
deviated, causing one nostril to appear larger than the other. 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). They also connect the nose to the throat (the nasopharynx), aiding in respiration. Though all four nostrils were on the outside the head of the aquatic ancestors of modern tetrapods, the nostrils for outgoing water (excurrent nostrils) migrated to the inside of the mouth, as evidenced by the discovery of ''
Kenichthys campbelli'', a 395-million-year-old fossilized fish which shows this migration in progress. It has two nostrils between its front teeth, similar to human
embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
s at an early stage. If these fail to join up, the result is a
cleft palate.
Each external nostril contains approximately 1,000 strands of
nasal hair, which function to filter foreign particles such as pollen and dust.
It is possible for humans to smell different
olfactory
The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste.
In humans, it ...
inputs in the two nostrils and experience a perceptual rivalry akin to that of
binocular rivalry when there are two different inputs to the two eyes.
The
Procellariiformes are distinguished from other birds by having tubular extensions of their nostrils.
Widely-spaced nostrils, like those of the
hammerhead shark, may be useful in determining the direction of an odour's source.
See also
*
Dilator naris muscle
*
Nasal cycle
References
External links
*
{{Authority control
Nose
Facial features