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| | Fall'96Syllabus |
 | | In Eusthenopteron (a representative osteolepiform) and the tetrapods, each nasal cavity consists of a junction of three ducts (surrounded by bone) which mutually connect the external naris (homologous with the anterior naris of most fish), orbit (eye socket), and internal naris (choana, which opens into the mouth cavity en route to the trachea). |
 | | The small size of the external naris in Eusthenopteron suggests that the primary adaptive benefit of the choana was improved smelling capability; most respiration was would still have been conducted through the mouth. |
 | | In view of the skull, the external naris of Acanthostega is small, suggesting that, like Eusthenopteron, it was primarily a mouth breather. |
| ijolite.geology.uiuc.edu /00FallClass/geo143/lect/lect12.html (1075 words) |
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