The Auditory (Eustachian) Tubes.
Along the lateral walls of the nasopharynx are the openings to the auditory tubes (= Eustachian or pharyngotympanic tubes).
Each narrow tube connects the nasopharynx with middle ear structures inside the air-filled tympanic cavity of the temporal bone.
You can open your auditory tubes by moving your mouth and neck muscles, such as yawning. When this occurs, air can flow between the middle ear and the nasopharynx.
This process equalizes the pressure on both sides of the eardrum (= tympanic membrane), making it easier for the eardrum to vibrate in response to sound waves.