The diagrams above show muscles in the mouth area that are not strictly speaking muscles of facial expression. There are more muscles in these areas than illustrated here. Top: Pterygoids and Hyoids. 2nd: Pterygoids.
3rd: Pterygoids from inside jaw. Last: Hyoids and hyoid bone.
The Pterygoid muscles, internal and external, are muscles of mastication and function to position the jaw.
and Geniohyoid help position the hyoid bone and larynx, and are important in swallowing.