Depressor anguli oris

The depressor anguli oris muscle (also known as the triangularis muscle) is an inverted triangular-shaped facial muscle of the oral group responsible for pulling the angle of the mouth downward and laterally, thus enabling facial expressions associated with frowning. At the origin site, its fibers can interdigitate with the fibers of the platysma muscle, and both these muscles work in conjunction with the platysma, which also has a depressor function.