Masseter muscle

The masseter muscle extends from the zygomatic arch to the ramus and body of the mandible.The insertion of this muscle is broad extending from the region of the second molar on the lateral surface of the mandible to the posterior lateral surface of the ramus.The masseter muscle is covered partly by the platysma muscle and by the risorius muscle.The platysma is activated during firm clenching.It also has some insertion in the orbicularis muscle and so is active in facial expression.The superficial part of the masseter muscle is seperated  only from the deeper layer at the posterior upper part of the muscle.The masseter muscle is covered mostly by the parotid gland tissue.The center of the lower third of the masseter muscle is 2 to 3 cms from the anterior border of the sternocleidomastoid muscle muscle which contracts during clenching in some individuals.The masseter muscle is active during forceful jaw closing and may assist in protrusion of the mandible.The masseter is innervated by the fifth or the masseter nerve.