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The nasalis is one of the muscles in the nose and is made up of two parts, the transverse, or compressor naris, and the alar, or depressor naris. Nostrils are compressed and drawn toward the septum by the transverse part of the nasalis. The alar part dilates, or flares, the nostrils.
Transverse means “lying across” and describes the thin, triangular part of the muscle that attaches at the maxilla, or upper jaw. It attaches to a thin tendon-like structure, or aponeurosis, across the bridge of the nose. The alar, or “wing-like” part of the nasalis, attaches at one end to the greater alar cartilage lying on the nose just above the nostril, and attaches at the other end to the skin on the tip of the nose. Like all the facial muscles, the nasalis is innervated by the upper buccal branches of the facial nerve, or cranial nerve VII. Blood is supplied by the facial artery.
When breathing is difficult, the nasalis muscle may widen the nostrils to help air pass more freely through. The muscle also plays a role in the formation of facial expressions from smiling to frowning. It often works with the assistance of other muscles of the nose, like the procerus, the levator labii superioris alaeque nasi, and the depressor septi nasi.
The procerus is another nasal muscle that wrinkles the top of the nose and pulls the eyebrows downward during frowning or squinting. It helps the nasalis pull the nostrils outward, flaring them in an expression of anger. Nicknamed the “Elvis muscle” because of its role in making a snarling expression, the levator labii superioris helps dilate the nostrils. The depressor septi nasi attaches to the septum at one end and above the incisors in the upper jaw at the other end and helps to pull the tip of the nose downward and to flare the nostrils.
After a cosmetic injection of a product such as Botox® into the forehead, the nasalis may overcompensate for the loss of forehead muscle movement and contract forcefully during facial expressions. This may cause an unintentional side effect of cosmetic surgery known as bunny lines, or horizontal wrinkles across the bridge of the nose that may appear during a smile. Bunny lines can also develop naturally with age. To prevent these wrinkles a doctor may inject Botox® into the transverse nasalis to paralyze the muscle.