Opening of mouth is caused by:

Ans. A Lateral pterygoidRef: Grays, 41st ed. pg. 507-508* The primary function of the lateral pterygoid muscle is to pull the head of the condyle out of the mandibular fossa along the articular eminence to protrude the mandible.* The effort of the lateral pterygoid muscles acts in helping lower the mandible and open the jaw whereas unilteral action of a lateral pterygoid produces contralateral excursion (a form of mastication), usually performed in concert with the medial pterygoids.* Unlike the other three muscles of mastication, the lateral pterygoid is the only muscle of mastication that assists in depressing the mandible i.e. opening the jaw. At the beginning of this action it is assisted by the digastric, mylohyoid and geniohyoid muscles.