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The ethmoidal sinuses or ethmoidal air cells of the ethmoid bone are one of the four paired paranasal sinuses. They are a variable in both size and number of small cavities in the lateral mass of each of the ethmoid bones and cannot be palpated during an extraoral examination.〔Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, page 64〕 They are divided into the anterior, middle and posterior groups (see below). The ethmoidal air cells consist of numerous thin-walled cavities situated in the ethmoidal labyrinth and completed by the frontal, maxilla, lacrimal, sphenoidal, and palatine bones. They lie between the upper parts of the nasal cavities and the orbits, and are separated from these cavities by thin bony laminae.〔 ==Groups of sinuses== The groups of the ethmoidal cells are air cells:〔Otorhinolaryngology, Head and Neck Surgery, Anniko, Springer, 2010, page 188〕 * The ''posterior group'' (sometimes the ''posterior ethmoidal sinus'') drains into the superior meatus above the middle nasal concha; sometimes one or more opens into the sphenoidal sinus. * The ''middle group'' (sometimes the ''middle ethmoidal sinus'') drains into the middle meatus of the nose on or above the bulla ethmoidalis. * The ''anterior group'' (sometimes the ''anterior ethmoidal sinus'') drains into the middle meatus of the nose by way of the infundibulum. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ethmoid sinus」の詳細全文を読む スポンサード リンク
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