The masseter muscle is a thick, rectangular muscle located in the cheek region of the face, near the angle of the mandible (lower jaw). It is the strongest muscle of mastication and is responsible for elevating the mandible and closing the jaw during biting and chewing. The superficial portion of the masseter muscle is the outermost layer of the muscle and is responsible for the initial part of jaw closure. The muscle originates from the zygomatic arch and inserts into the ramus and angle of the mandible. The masseter muscle is innervated by the mandibular branch of the trigeminal nerve (cranial nerve V) and works in conjunction with other muscles of mastication, such as the temporalis and medial pterygoid muscles, to produce efficient jaw movements during mastication. Dysfunction or weakness of the masseter muscle can lead to difficulties chewing and opening the mouth.