A nostril (or naris , : nares ) is either of the two orifices of the

nose A nose is a sensory organ and respiratory structure in vertebrates. It consists of a nasal cavity inside the head, and an external nose on the face. The external nose houses the nostrils, or nares, a pair of tubes providing airflow through the ...

. They enable the entry and exit of air and other gasses through the nasal cavities. In

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

s and

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s, they contain branched bones or cartilages called

turbinate In anatomy, a nasal concha (; : conchae; ; Latin for 'shell'), also called a nasal turbinate or turbinal, is a long, narrow, curled shelf of bone that protrudes into the breathing passage of the nose in humans and various other animals. The con ...

s, whose function is to warm air on inhalation and remove moisture on exhalation.

Fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

do not breathe through noses, but they do have two 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 (with the exception of

Cyclostomi Cyclostomi, often referred to as Cyclostomata , from Ancient Greek κύκλος (kúklos), meaning "circle", and στόμα (stóma), meaning "mouth", is a superclass of vertebrates that comprises the living jawless fish classes: the lamp ...

, which have just one nostril). In

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

s, the

nasal cycle The nasal cycle is the subconscious alternating partial Nasal congestion, congestion and decongestion of the nasal cavity, nasal cavities in humans and other animals. This results in greater airflow through one nostril with periodic alternation ...

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 language, Latin for ''something that encloses''; septa) is a wall, dividing a Body cavity, cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Hum ...

. 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

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

s, 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

choana The choanae (: 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 ...

e). They also connect the nose to the throat (the nasopharynx), aiding in respiration. Though all four nostrils were on the outside of 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

lobe-finned fish Sarcopterygii (; )—sometimes considered synonymous with Crossopterygii ()—is a clade (traditionally a class or subclass) of vertebrate animals which includes a group of bony fish commonly referred to as lobe-finned fish. These vertebrates ar ...

which shows this migration in progress. It has two nostrils between its front teeth, similar to human

embryo An embryo ( ) is the initial stage of development for 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 sp ...

s at an early stage. If these fail to join up, the result is a

cleft palate A cleft lip contains an opening in the upper lip that may extend into the nose. The opening may be on one side, both sides, or in the middle. A cleft palate occurs when the palate (the roof of the mouth) contains an opening into the nose. The ...

. 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 Binocular rivalry is a phenomenon of visual perception in which perception alternates between different images presented to each human eye, eye. When one image is presented to one eye and a very different image is presented to the other (also kn ...

when there are two different inputs to the two eyes. Furthermore, scent information from the two nostrils leads to two types of neural activity with the first cycle corresponding to the ipsilateral and the second cycle corresponding to the contralateral odor representations. In some cultures the extreme wide flaring of the nostrils accompanied by the baring of the upper teeth is often referred to as "doing the nostrils." The

Procellariiformes Procellariiformes is an order (biology), order of seabirds that comprises four family (biology), families: the albatrosses, the Procellariidae, petrels and shearwaters, and two families of storm petrels. Formerly called Tubinares and still call ...

are distinguished from other birds by having tubular extensions of their nostrils. Widely-spaced nostrils, like those of the

hammerhead shark The hammerhead sharks are a group of sharks that form the family Sphyrnidae, named for the unusual and distinctive form of their heads, which are flattened and laterally extended into a Hammerhead shark#Cephalofoil, cephalofoil (a T-shape or " ...

, may be useful in determining the direction of an odour's source.

References

External links

* {{Authority control Nose Facial features Otorhinolaryngology Respiratory system anatomy

See also

References

External links