Which muscle depresses the jaw?

• A. Masseter
• B. Temporalis
• C. Medial pterygoid
• D. Lateral pterygoid

Answer: (D)

Opening the mouth relies on a muscle that pulls the mandible downward and forward. The lateral pterygoid is the one that directly depresses the jaw by pulling the mandibular condyle anteriorly and inferiorly, which helps to open the mouth and protrude the jaw. It also helps maintain the proper disc position at the TMJ during movement.

The other muscles listed are involved in closing the jaw: the masseter elevates the mandible to bite, the temporalis elevates (and can retract) the mandible, and the medial pterygoid elevates the mandible and assists with grinding. So, the lateral pterygoid is the muscle responsible for depressing the jaw.