Which of the following muscles is primarily involved in the action of chewing?

The temporalis muscle plays a crucial role in the action of chewing, known as mastication. This fan-shaped muscle is situated on the side of the skull and is one of the primary muscles responsible for elevating the mandible (lower jaw) to close the mouth. It helps facilitate the grinding and crushing of food, making it essential for effective chewing.

In the context of the other muscles listed, the mentalis muscle is primarily responsible for the movement of the lower lip and chin, while the triangularis muscle (part of the depressor anguli oris) is involved in pulling down the corners of the mouth, contributing to facial expressions like sadness. The zygomaticus muscle is associated with smiling and lifting the corners of the mouth. None of these muscles are primarily involved in chewing, which highlights the specialized function of the temporalis in this specific action.