Compresses bridge, depresses tip of nose, elevates corners of nostrils
The nasalis is a sphincter-like muscle of the nose whose function is to compress the nasal cartilage. It is the muscle responsible for "flaring" of the nostrils.
It consists of two parts, transverse and alar:
The transverse part (compressor naris) arises from the maxilla, above and lateral to the incisive fossa; its fibers proceed upward and medially, expanding into a thin aponeurosis which is continuous on the bridge of the nose with that of the muscle of the opposite side, and with the aponeurosis of the Procerus. It compresses the nostrils and may completely close them.
The alar part "Dilator nasalis". arises from the maxilla over the lateral incisor and inserts into the greater alar cartilage. Its medial fibres tend to blend with the depressor septi, and has been described as part of that muscle.