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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.



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.

References in periodicals archive ?
Nevertheless, as the main focus here is the phylogenetic relationships of Nyctiphruretus, the sister-group relationship of Nyctiphruretus with the clade consisting of the other non-pareiasaurian Mezen river parareptiles and pareiasaurs, found in five of the six MPTs, is diagnosed by the following four synapomorphies: median postparietal (5:0, unambiguous), choana curved postero-medially; palatine forms its posterior and part of lateral edge (42:1), alar flange of the vomer present (43:1), and transverse processes or ribs present on at least thirteen caudals (98:1).
The procedure involved direct visualization of the choana with 0 degree Hopkins rod endoscope and the choanal atretic plate, which was partially bony and membranous was excised with the assistance of microsurgical debrider.
The primary location of the fungal plaques depends on the course of the infection and can begin in the air sacs, lungs, or upper respiratory tract (eg, nares, choana, larynx, trachea, and syrinx).
Figure 2: Showing a soft tissue density in the anterior part of right nasal cavity (arrow head) and mucosal thickening in the right maxillary sinus and choana and nasopharynx free.
Histopathologic examination showed large sheets of neoplastic lymphocytes expanding and infiltrating the parenchyma of multiple organs, including eyes (Fig 2), spleen, liver, kidneys (Fig 3), proventriculus (Fig 4), intestines, pancreas, and choana.
Posterior rhinoscopy showed same mass occupying the right choana and it was extending into nasopharynx.
8) % in females; supratympanic fold thin, ending just behind tympanum; two postrictal tubercles, nearest subconical; choanae round, not concealed by palatal shelf of maxillary arch; odontophores median and posterior to choanae, approximately twice size of a choana, subtriangular in outline, elevated, separated medially by distance 2/ 3 width of odontophore, bearing transverse row of up to 4-5 teeth; tongue longer than wide, posterior edge with shallow notch, posterior 1/3 not adherent to floor of mouth; males with short vocal slits posterolateral to tongue.
Histologic examination revealed deep focal necrosis of the choana, reaching into the submucosal layer.
After resection at its origin, it was found to be filling the inferior right nasal airway (figure 2, A) and extending back to the right posterior choana.
Diagnostic nasal endoscopy showed a thin streak of blood coming from left maxillary sinus ostium and tracking towards choana.
To compare a calculated dose of radiation intended to be administered and the actual amount of radiation delivered to the target area of the choana in 3 adult military macaws (Ara militaris), computed tomography scans were obtained and the monitor unit was calculated to deliver 100 cGy (lGy) by using radiation planning software.