The nasalis muscle, also termed the naris muscle, is divided into two parts: compressor nasalis and dilator nasalis. Both are innervated by the buccal branch of the facial nerve.
Compressor nasalis arises from the frontal part of the maxilla just superior to the upper incisors on each side. It runs roughly medially and transversely to an aponeurosis on the dorum of the nose. It acts to close the aperture of the nostril.
Dilator nasalis arises from the the frontal part of the maxilla at a slightly superior point to compressor nasalis on each side. It runs medially and slightly inferiorly to insert into the ipsilateral alar cartilages. It acts to open the aperture of the nostril.
The nasalis muscles are used as accessory muscles of respiration during times of respiratory distress; they are partially responsible for 'nasal flaring'.