Complex sentence: The upper head originates on the infratemporal surface of the sphenoid bone, and the lower head on the lateral surface of the lateral pterygoid plate; both insert onto the pterygoid fovea under the condyloid process of the mandible.
Split into simpler sentences: The upper head originates on the infratemporal surface of the sphenoid bone, and the lower head on the lateral surface of the lateral pterygoid plate. Both heads insert onto the pterygoid fovea under the condyloid process of the mandible.