Which of the following muscles is NOT a muscle of mastication?

The correct choice identifies the frontalis muscle as not being a muscle of mastication. Mastication refers to the process of chewing, and the primary muscles involved in this action are specifically designed to move the jaw. The lateral pterygoid, masseter, and temporalis muscles all play crucial roles in moving and stabilizing the jaw during the chewing process.

The lateral pterygoid muscle helps in depressing and protracting the mandible, allowing the jaw to open. The masseter is one of the strongest muscles in the body, responsible for elevating the mandible, which closes the jaw. The temporalis muscle aids in elevating and retracting the mandible, further contributing to its role in chewing.

In contrast, the frontalis muscle is located in the forehead region and is primarily responsible for raising the eyebrows and wrinkling the forehead. It is not involved in mastication or any movements of the jaw, thus qualifying it as the correct answer in distinguishing it from the muscles that facilitate chewing.