The masseter is a thick, quadrate muscle in the cheek which arises from the lower border and deep surface of the zygomatic arch and extends to the mandible. It is important for mastication (chewing) and acts by closing the jaws.
The deep fibers of the masseter are vertical; the superficial fibers pass downward and backward. It is inserted into the lateral surface of the ramus and coronoid process of the mandible and completely conceals them; however, it is does not cover the head and neck of the mandible, and these can be felt behind it.
The masseter raises the mandible and helps to protract it. Its nerve is derived from the mandibular nerve.