Four muscles are used to chew food. They are the masseter, temporalis, medial pterygoid and lateral pterygoid. These muscles are responsible for the chewing action, moving the mandibles from side to side, grinding teeth and even helping us speak. They are also referred to as "muscles of mastication."
Chewing muscles can be further classified as deep and superfificial muscles of mastication. The deep muscles are the temporalis and the deep masseter. They are so called because they are partially hidden by bone. These two muscles work to pull the mandible up towards the maxillae when you chew.
The superficial muscles of mastication are the lateral pterygoid, the medial pterygoid and the superficial masseter. The superficial masseter is responsible for raising the mandible against the maxillae with force, and the medial pterygoid and the lateral pterygoid draw the mandible forward.