The depressor anguli oris muscle (triangularis muscle) is a facial muscle. It originates from the mandible and inserts into the angle of the mouth. It is associated with frowning, as it depresses the corner of the mouth.
Structure
The depressor anguli oris arises from the lateral surface of the mandible.[1] Its fibers then converge. It is inserted by a narrow fasciculus into the angle of the mouth.[1] At its origin, it is continuous with the platysma muscle, and at its insertion with the orbicularis oris muscle and risorius muscle. Some of its fibers are directly continuous with those of the levator anguli oris muscle, and others are occasionally found crossing from the muscle of one side to that of the other; these latter fibers constitute the transverse muscle of the chin.
The depressor anguli oris muscle receives its blood supply from a branch of the facial artery.
Underdevelopment (hypoplasia) or complete absence (aplasia) of the depressor anguli oris can occur.[2] Similarly to paralysis, individuals with these conditions will have an asymmetric smile.[medical citation needed] These conditions are rare, and develop at or before birth (congenitally).
