The bulk of the muscle arises as a deep head from just above the medial surface of the lateral pterygoid plate.

The smaller, superficial head originates from the maxillary tuberosity and the pyramidal process of the palatine bone.

Its fibers pass downward, lateral, and posterior, and are inserted, by a strong tendinous lamina, into the lower and back part of the medial surface of the ramus and angle of the mandible, as high as the mandibular foramen.

The medial pterygoid muscle has functions including elevating the mandible (closing the mouth), protruding the mandible, mastication (especially for when the maxillary teeth and the mandibular teeth are close together),[1] and excursing the mandible (contralateral excursion occurs with unilateral contraction).

This article incorporates text in the public domain from page 387 of the 20th edition of Gray's Anatomy (1918)