Which muscle extends along the side of the chin and draws the corner of the mouth down?

The muscle that extends along the side of the chin and draws the corner of the mouth down is known as the triangularis muscle. This muscle plays a significant role in facial expressions, particularly in conveying emotions such as sadness or frowning. When the triangularis contracts, it depresses the corners of the mouth, which visibly alters the expression of the face.

The triangularis is located just below the mouth, and its action is essential for movements that require the downward pull of the lips. Understanding the function of this muscle is important for estheticians, as they often need to assess facial musculature and may incorporate this knowledge into their practice when considering treatments that affect facial expressions.

The other muscles listed have different functions and are situated in various areas of the face. The orbicularis oris encircles the mouth and is responsible for actions like pursing the lips. The buccinator is located in the cheek area and aids in processes such as chewing by pushing food toward the molars. The zygomaticus muscles, situated higher in the face, are responsible for smiling, as they lift the corners of the mouth upward. Therefore, recognizing the specific action of the triangularis distinguishes it as the correct answer in this context.