Muscle, which pulls the disk of TMJ downward:
Lateral pterygoid is the only muscle of mastication, which is inserted into anterior margin of articular disc and capsule of TMJ by lower head and to pterygoid fovea of neck of mandible, by superior head.
It pulls the disk of TMJ downwards, depressing the mandible.
Lateral pterygoid
Medial pterygoid
Digastric
Mylohyoid