Anterior naris

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The anterior (or external) nares (singular: naris) (or nostrils) form the entrance to the nose. Each naris is formed by a ring of structures:

medially the columella (soft tissue anteroinferior portion of the nasal septum)
laterally and superiorly the nasal ala
inferiorly the nasal sill

By virtue of the actions of the compressor naris and the dilatator naris muscles the nostrils are narrowed or flared respectively.