Nasalis muscle

Origin and insertion

Nasalis muscles are found on each side of the midline, respectively. Each muscle is composed of two parts; lateral or transverse part (compressor naris) and medial or alar part (dilator naris posterior). 

The transverse part covers the dorsum of the nose. It originates from the maxilla, attaching superolateral to the incisive foramen. Its fibers then course superomedially, expanding into a thin aponeurosis at the bridge of the nose. Via this aponeurosis, the muscle inserts at the dorsum of the nose by blending with its counterpart from the opposite side.

The alar part comprises the nostrils. It originates from the frontal process of maxilla, just superior to the lateral incisor. After a short superoanterior course, it inserts to the skin of ala, superior to the lateral crus of major alar cartilage. Here, some fibers blend with the transverse part of nasalis.

Relations

Nasalis lies superficial to the nasal bone and lateral nasal cartilage, being covered by the nasal skin. The inserting fibers of its transverse part are directly related to, and may partially blend with, the aponeurosis of procerus muscle. The alar part lies lateral to the depressor septi muscle.

A small muscle called dilator nasi anterior, or apicis nasi, attaches to the anterior margin of the alar part of nasalis muscle. Several arteries and nerves course over the superior surface of nasalis including, the facial artery, terminal branches of the infraorbital artery and nerve, and the external nasal artery and nerve.

Innervation

Nasalis muscle is innervated by the buccal branch of facial nerve (CN VII).

Blood supply

Blood supply to nasalis comes from the superior labial, septal and lateral nasal branches of facial artery, and the infraorbital branch of maxillary artery.

Function

The transverse part of nasalis wrinkles the nasal skin and compresses the nasal aperture, hence its other name compressor naris. The alar part dilates the nostrils as it pulls the ala laterally, thus its name dilator naris posterior.

All these actions of nasalis normally happen prior to each inspirium, in order to prevent the external nasal valve from collapsing. This function of nasalis is even more notable during deep breathing when these movements are more obvious, as well as in affective emotional states such as anger.