The nasalis is a muscle of the nose that contracts and dilates the nasal cartilages. It is made up of two parts, transverse/compressor and alar/dilator parts. It is structurally similar to a sphincter.
- The transverse part also known as compressor naris emerges superiorly and laterally towards the incisive fossa via the maxilla; its fibers continue superiorly and medially, spreading into a thin aponeurosis which is constant on the bridge of the nose and the muscle of the opposite side. It compresses the nostrils and may completely close them.
- The alar part part also known as dilator nasalis emerges via the maxilla superior towards the lateral incisor. Its medial fibres are likely to blend with the depressor septi.
- Transverse part – It is constant with the same muscle of the other side of the face. The two muscles merge superior towards the middle segment of the anterior margin of the nose over the cartilaginous portion.
- Alar part – It attaches with:
- The skin on the posterior end of the wing of the nose.
- The skin at the posterior margin of the nostril.
- The skin of the mobile septum of the nose at the midline.
- The transverse part of the nasalis is a slim muscle which hooks.
- Posterior towards the wing of the nose.
- Deep towards the levator labii superioris alaeque nasi.
- Near the skull and then widens into a triangular shape as it travels superiorly, anteriorly, and medially on the side of the nose.
- It ends in a wide aponeurosis.
- The alar part of the nasalis is a short, wide muscle. It is enclosed by the upper part of the orbicularis oris.
The buccal branch of the facial nerve innervates the nasalis muscle.
- Transverse part: The arising and attaching points of the transverse part have no movement; so, when the transverse portion constricts and its belly flattens in the middle of its two immovable points of attachment. As neither end moves, the muscle compresses the side of the nose, but not the nostrils. Whenever the lips are strongly pressed together the muscle mechanically narrows. Both transverse parts constrict all together on each side of the face.
- Alar part: Pulls its attachment points inferiorly. Both alar parts of the nasalis contract concurrently at both sides of the face. In the same manner the mentalis impulses the lower lip superiorly; when the lips are pressed together, the alar portions of the nasalis push the upper lip inferiorly.
Both parts of the nasalis seem to always contract together, and are regularly used in speech whenever the lips are compressed together, for example in speaking “B” and “P” sounds.