Which muscle pulls the corners of the mouth downward and is also known as the Triangularis?

• A. Levator Anguli Oris
• B. Depressor Anguli Oris
• C. Depressor Labii Inferioris
• D. Levator Labii Muscle

Answer: (B)

This is about the muscle actions that shape the mouth. The one that pulls the corners of the mouth downward is the depressor anguli oris, also known as triangularis. It runs from the lower jaw up to the angle at the corner of the mouth, and its fibers pull the corners downward and slightly inward, creating a frown. Its triangular shape is where the nickname comes from.

Think of what happens when you smile versus when you frown: the muscle that elevates the corners of the mouth is the levator anguli oris, which lifts the sides to form a smile. In contrast, the depressor labii inferioris pulls down the lower lip rather than moving the mouth corners, and the levator labii superioris raises the upper lip. So the downward pulling of the mouth corners is specifically the action of the depressor anguli oris.