The masseter is a three bellied muscle on the lateral jaw. It is often regarded as having the strongest muscle fibers in the body.
Origin: The anterior two-thirds of the zygomatic arch along the maxilla and temporal bones,
Insertion: The anterior belly attaches along the anterior surface of the mandible in front of the attachment of the deep belly. The posterior belly attaches to the surface of the ramus behind the attachment of the deep belly
Origin: The posterior third of the zygomatic arch along the zygomatic process of the temporal bone.
Insertion: The lateral surface of the coronoid process of the mandible.
Function: Elevate the mandible and close the jaw.
Wikipedia entry for masseter.