Answer
The masseter is the prime mover of the action of jaw closing. It elevates the mandible, and its actions are essential for biting and eating.
The temporalis muscle elevates and retracts the mandible; it maintains the proper position of the mandible at rest .
Work Step by Step
Only the lateral pterygoids open the mouth, but the force of gravity tends to cause the mandible to fall inferiorly and the mouth to open . This is especially so if the masseter and temporalis are weakened by age or disease, or are relaxed during sleep. If the masseter and temporalis malfunction, closing the mouth would be difficult, and eating would become a problem.
