Nasalis

Nasalis is a superficial facial muscle that covers the nasal aperture. It consists of two parts: the transversus nasi (transverse part) and the alaris nasi (alar part). The transversus nasi originates from the maxilla near the nose and from the nasal aponeurosis, courses horizontally across the dorsum of the nose, and inserts into the nasal aponeurosis on the opposite side. Its primary action is to compress the nostrils, narrowing the nasal opening when it contracts. The alaris nasi arises from the maxilla near the lateral aspect of the nose and blends with the alar cartilage, extending to the alar region of the nostril. Its fibers act to flare or widen the nostrils by pulling the nasal wings downward and laterally.

Innervation is via the facial nerve (cranial nerve VII), typically through the buccal branches. Blood supply comes from branches of the facial artery, with possible contribution from infraorbital vessels.

In humans, the nasalis is a small, variable muscle contributing to nasal contour and airflow control during breathing and facial expression. Its size and prominence can vary between individuals, and in some people the muscle may be underdeveloped or absent.

Overall, nasalis refers to a two-part facial muscle of the nose that modulates nostril aperture through opposing actions of its transverse and alar components, under voluntary and reflexive control by the facial nerve.