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Choana
Base of skull. Inferior surface. (Choana is labeled in gray recess approximately 1/3 of the way from the top, at center.)
Dissection of the muscles of the palate from behind. (Choanae visible at center top.)
subject #47 196
Dorlands/Elsevier c_28/12234217
Choana (plural: Choanae) is the posterior nasal aperture.

The choanae are separated by the vomer.

Boundaries

It is the opening between the nasal cavity and the nasopharynx.

It is therefore not a structure but a space bounded as follows:

Etymology

The term is a latinization from the Greek "choanē" meaning funnel.

Choanae in different animals

The only animals with choana are the tetrapoda, and they could as well be called Choanata (they are also the only ones with a vomeronasal organ, which has an embryonic origin from the olfactory structure).

These internal nasal passages evolved while the vertebrates still lived in water. At this point they already needed to gulp air to get enough oxygen, and rather than open their jaws each time to do this, some groups acquired small openings to breathe through as a better design.

Fish

Fish don't have choana, instead they have a pair of external nostrils: two tubes whose frontal openings lie close to the upper jaw, and the posterior openings further behind near the eyes.

A 400-million-year-old fossil lobe-finned fish called Kenichthys campbelli has something between a choana and the external nostrils seen on other fish, which makes it look like it has a cleft palate or cleft lip. The reason seems to be that the posterior opening of the external nostrils has migrated into the mouth for some reason.

Tetrapods

Similar migration is still seen in the tetrapod embryo, and can cause a baby to be born with a cleft palate. Why it should migrate is a mystery, since the nostrils would be useless as a breathing device before their final position inside the mouth. They could also already breath air through their spiracles.

Tetrapods are also equipped with a lacrimal duct, or tear duct. How it evolved is not known, but it has an internal connection with the choana. It's possible that the choana started as a natural crack between maxilla and premaxilla because of an incomplete fusion in air breathing animals. If this gap got wider and deeper with time, the frontal part of it would have to fuse together to avoid weakening the upper jaw, creating a small opening on the upper lip. Some more migrating, and this gap would meet the anterior pair of the external nasal openings. The posterior pair of the openings was then free to form the lacrimal duct if a migration caused them to come in contact with the eyes.

Choanae analogues in other animals and fossils

This wouldn't been the first time the jaws evolved some sort of opening. For instance, snakes have evolved a cleft in the lower jaw, allowing them to stick out their tongue without having to open the jaw. For an animal living in water, the formation of a paired cleft on the upper jaw would be quite logical. Terrestrial vertebrates would in any case need a way to breath without needing to open their jaws each time.

Some fossil species are said to have both conventional external nostrils and a choana, but only more fossils will give a real answer to how the choanas evolved.

Lungfish and hagfishes

In addition to tetrapods, the lungfish has internal nostrils too. These seem to have a different origin than those of the tetrapods, and lungfish have no tear duct either.

Hagfishes have a single internal nostril that opens inside the mouth cavity, while Chimaerae have open canals that leads water from their external nostrils into their mouth and through their gills.

References

 •  • [ e]
General anatomy of head and neck - head
Face/OcciputForehead • Eye • Ear • Temple • Cheek • Chin
External noseNostril • Nasal septum • Cartilages (Accessory nasal, of the septum, Greater alar, Lateral nasal, Lesser alar, Vomeronasal)  • Olfactory glands
Nasal cavityChoana • Turbinate • Sphenoethmoidal recess • Ethmoid bulla • Hiatus semilunaris • Ostium maxillare • Inferior meatus • Vomeronasal organ • Paranasal sinus
Mouth/oral cavityLip • Philtrum • Jaw • Pterygomandibular raphe
TeethPermanent (Incisor, Canine, Premolar, Molar)  • Deciduous
TonguePlica fimbriata • Median sulcus • Foramen cecum • Terminal sulcus • Frenulum linguae • Anterior tongue • Posterior tongue
Palate/roof of mouthHard palate • Soft palate • Palatine raphe • Incisive papilla • Uvula • Pharyngeal recess • Arches: (Palatoglossal • Palatopharyngeal)
Salivary glands(Parotid • Sublingual • Submandibular) • Ducts: Submandibular • Parotid
fasciaMasseteric fascia • Temporal fascia • Galea aponeurotica • Scalp
Elsevier, the world's largest publisher of medical and scientific literature, forms part of the Reed Elsevier group. Based in Amsterdam, the company has substantial operations in the UK, USA and elsewhere.
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The vomer (from Latin vomer, -ĕris, "ploughshare") is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and touches the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones.
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The nasal cavity (or nasal fossa) is a large air-filled space above and behind the nose in the middle of the face.

Function

The nasal cavity conditions the air to be received by the areas of the respiratory tract.
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The nasopharynx (nasal part of the pharynx) lies behind the nose and above the level of the soft palate: it differs from the oral and laryngeal parts of the pharynx in that its cavity always remains patent (open).
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In sciences dealing with the anatomy of animals, precise anatomical terms of location are necessary for a variety of reasons. Non-scientists often wonder why zoological and human anatomists use complex terminology to describe locations on a body, when common terms like "up",
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The horizontal part of the palatine bone (horizontal plate) is quadrilateral, and has two surfaces and four borders.

Surfaces

The superior surface, concave from side to side, forms the back part of the floor of the nasal cavity.
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The palatine bone is a bone in the palate (Latin palatum; unrelated to palatium 'palace', from which other senses of palatine derive).

Anatomy

It is situated at the back part of the nasal cavity between the maxilla and the pterygoid process of the
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The sphenoid bone (from Greek sphenoeides, "wedgelike") is a bone situated at the base of the skull in front of the temporals and basilar part of the occipital bone.

The sphenoid bone somewhat resembles a butterfly or bat with its wings extended.
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The medial pterygoid plate (or medial pterygoid lamina) of the sphenoid is narrower and longer than the lateral pterygoid plate; it curves lateralward at its lower extremity into a hook-like process, the pterygoid hamulus, around which the tendon of the Tensor veli palatini
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funnel is a pipe with a wide, often conical mouth and a narrow stem. It is used to channel liquid or fine-grained substances into containers with a small opening. Without a funnel, much spillage would occur.

Funnels are usually made of stainless steel, glass, or plastic.
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Tetrapoda
Broili, 1913

Classes
  • Amphibia
  • Aves
  • Mammalia
  • Sauropsida (Reptilia)
  • Synapsida
Tetrapods (Greek tetrapoda, Latin quadruped
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The vomeronasal organ (VNO) or Jacobson's organ[1] is an auxiliary olfactory sense organ in some tetrapods. It is the first processing stage of the accessory olfactory system. In adults, it is located in the vomer bone, between the nose and the mouth.
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Dipnoi
Müller, 1844

Orders

See text.
Lungfish are freshwater fish belonging to the order Dipnoi. Lungfish are best-known for retaining characteristics primitive within the Osteichthyes, including the ability to breathe air, and structures primitive
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Myxini

Order: Myxiniformes

Family: Myxinidae

Genera

Eptatretus
Myxine
Nemamyxine
Neomyxine
Notomyxine

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Chimaeriformes

Families
See text for families, genera and species.

Chimaeras are cartilaginous fish in the order Chimaeriformes. They are related to the sharks and rays, and are sometimes called ghost sharks, ratfish
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eMedicine is an online clinical medical knowledge base that was founded in 1996 by Scott Plantz and Richard Lavely, two medical doctors. It was sold to WebMD in January 2006.
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Human anatomy is primarily the scientific study of the morphology of the adult human body.[1] It is subdivided into gross anatomy and microscopic anatomy.[1]
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Head and neck anatomy focuses on the structures of the head and neck of the human body, including the brain, bones, muscles, blood vessels, nerves, glands, nose, mouth, teeth, tongue, and throat.
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head of an animal is the rostral part (from anatomical position) that usually comprises the brain, eyes, ears, nose, and mouth (all of which aid in various sensory functions, such as sight, hearing, smell, and taste).
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The face is the front part of the head, in humans from the forehead to chin including the hair, forehead, eyebrow, eyes, nose, cheeks, mouth, lips, philtrum, teeth, skin, and chin. The face is used for expression, appearance and identity amongst others.
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The occiput is the anatomical term for the posterior portion of the head.

Clinical significance

Trauma to the occiput can cause a basilar skull fracture.

Identification of the location of the fetal occiput is important in obstetrics.
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In human anatomy, the forehead or brow is the bony part of the head above the eyes. People who have a large forehead are often said to have a fivehead.

Anatomy

In modern humans it is roughly vertical, ending at the hairline where the head flattens out.
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Eyes are organs of vision that detect light. Different kinds of light-sensitive organs are found in a variety of organisms. The simplest eyes do nothing but detect whether the surroundings are light or dark, while more complex eyes can distinguish shapes and colors.
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outer ear is the most external portion of the ear. The outer ear includes the pinnae (also called auricle), the ear canal, and the very most superficial layer of the ear drum (also called the tympanic membrane).
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Temple indicates the side of the head behind the eyes. The bone beneath is the temporal bone.

Anatomy

Cladists classify land vertebrates based on the presence of an upper hole, a lower hole, both, or neither in the cover of dermal bone which formerly covered the
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Cheeks (Latin: bucca, also malā: "jaw") constitute the area of the face below the eyes and between the nose and the left or right ear.

It is fleshy in humans and other mammals, the skin being suspended by the chin and the jaws, and forming the lateral
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As an acronym, CHIN may refer to:
  • Canadian Heritage Information Network, a government agency in Canada which promotes Canadian culture and heritage on the Internet

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The factual accuracy of part of this article is disputed.
The dispute is about Nasology, which has been described as "an extended joke at the expense of Phrenology"''.

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nostril (or naris, pl. 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
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