The medial pterygoid mirrors the masseter on the deep side of the mandible. It also has two heads. The superficial head originates on maxillary tuberosity and the adjacent sphenoid bone. It runs vertically to insert on the inner surface of the angle and ramus of the mandible. This part is mainly involved with elevating the mandible. The deep part originates on the medial surface of the lateral pterygoid plate and inserts in the same area of the mandible. This origin is medial to the insertion so can contribute to rotating the mandible causing some side to side movement. Both heads originate anterior to the insertions so like the superficial head of the masseter it is involved in protruding the mandible. This muscle is in close proximity to the area where inferior alveolar nerve blocks are given and if injured during the injection is the main reason for post-injection limitation in the mandibular range of movement known as trismus.