posterior nasal apertureGo to external page http://purl.obolibrary.org/obo/UBERON_0004771
Opening/conduit between the nasal cavity and the nasopharynx[AAO] The choanae are separated by the vomer[WP]. [ http://en.wikipedia.org/wiki/Posterior_nasal_apertures AAO:0000093 ]
Synonyms: posterior nasal apperture
One of the paired openings from the nasal cavities into the pharynx. [Bemis_WE, Functional_Anatomy_of_the_Vertebrates:_An_Evolutionary_Perspective, Glossary_G-6, Grande_L, Liem_KF, Third_Edition_(2001)_Orlando_Fla.:_Harcourt_College_Publishers, Walker_WF][VHOG]
Opening between the nasal cavity and the nasopharynx.[AAO]
The choana, a unique 'internal nostril' opening from the nasal sac into the roof of the mouth, is a key part of the tetrapod (land vertebrate) respiratory system. It was the first component of the tetrapod body plan to evolve, well before the origin of limbs, and is therefore crucial to our understanding of the beginning of the fish-tetrapod transition. (...) Here we present new material of Kenichthys, a 395-million-year-old fossil fish from China, that provides direct evidence for the origin of the choana and establishes its homology: it is indeed a displaced posterior external nostril that, during a brief transitional stage illustrated by Kenichthys, separated the maxilla from the premaxilla.[well established][VHOG]
In addition to tetrapods, the lungfish has internal nostrils too. In tetrapods the exhalant nostril (choana) empties into the buccal cavity.
Fish don't have choanae, instead they have two pairs of external nostrils