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A funnel-shaped opening, especially the posterior nares.
(invertebrate zoology)
A protoplasmic collar surrounding the basal ends of the flagella in certain flagellates and in the choanocytes of sponges.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



an internal nasal orifice in vertebrates, including man. Choanae evolved after the development of constant or periodic breathing of air. They first arose in crossopterygian and dipnoan fish. In dipnoan embryos, grooves starting from the olfactory sacs change into canals whose internal orifices, or primary choanae, open into the oral cavity. In dipnoan fish, with aquatic respiration, air flows to the lungs through the canals. In terrestrial vertebrates, a naso-oral canal forms during embryonic development and connects with the external nasal orifices, or nostrils, to the oral cavity, where it opens into the primary choanae. In amphibians the choanae remain in this position throughout life. In mammals and in some reptiles and birds the upper part of the oral cavity into which the primary choanae open becomes separated from the lower part because of the development of the secondary hard palate; it forms the nasopharyngeal duct, which opens into the pharyngeal cavity through the secondary choanae. In crocodiles, some birds, and especially mammals the secondary choanae recede farther into the pharynx as the secondary hard palate lengthens. The formation of a nasopharyngeal duct separated from the lower part of the oral cavity and the recession of the choanae close to the larynx enable animals and humans to breathe freely when food is in the oral cavity.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
With the scope moving forward, a huge hypertrophic adenoid was found to block the choanae, and this was characterized as Grade 4 adenoid hypertrophy.
The nasal cavity in kenguri sheep has three nasal turbinate bones (choanae), viz.
Removal is usually achieved via anterior rhinoscopy or endoscopy, although a lateral rhinotomy approach has been required in select cases in which complete removal through the nostrils or the posterior choanae was not possible due to the large size of the mass (13).
Although this stork underwent a thorough physical examination, because of its attitude and size, good visualization of the choanae was not possible in the awake bird.
During necropsy, typical glanderous lesions in the lung, choanae, and nasal septae were observed.
After seeing 13 consultants, at the age of 14 months Jamie was also diagnosed with profound deafness and a severe form of Charge syndrome (Coloboma of the eye, Heart defects, Atresia of the choanae, Retardation of growth and/or development, Genital and/or urinary abnormalities, and Ear abnormalities and deafness).
Congenital deafblindness is often caused by a prenatal virus (e.g., congenital rubella) or chromosomal abnormalities (e.g., CHARGE syndrome; CHARGE stands for coloboma of the eye, heart defects, atresia of the nasal choanae, retardation of growth and/or development, genital and/or urinary abnormalities, and ear abnormalities and deafness).
The actual length and the ideal length were each measured at the piriform aperture, at the choanae, at half the distance from the tip of the nose to the piriform aperture, and at half the distance from the piriform aperture to the choanae (figure).
At posterior rhinoscopy there was visualized 4x6.5 cm reddish space-occupying lesion, with smooth surface overlapping 2/3 of both choanae. At digital investigation the lesion was of hard elastic consistence, with wide bottom, fixed to upper back wall of epipharynx, bleeding.
(29) based on common features of the syndrome: C-- coloboma of the eye (missing part of iris and/or retina); H--heart defects; A--atresia of the choanae (bony or membranous blocking of nasal passage); R--retardation of growth and/or development; G--genitourinary anomalies; E--ear anomalies and/or deafness.
The velopharynx closes to prevent food from entering the nasal cavity via the posterior choanae. The larynx is closed off to prevent food aspiration, allowing muscular contraction in the pharynx to move the food bolus down past the cricopharyngeal sphincter and into the esophagus.