Here is a good description of the ears, nose and throat from Johns Hopkins: https://www.hopkinsmedicine.org/healthlibrary/conditions/otolaryngology/ear_nose_and_throat_facts_85,P00448 About the sinuses, the site says:
The sinuses are four pairs of air-filled cavities that are also lined with mucous membranes. The problem is that these air-filled cavities sometimes fill up with fluid and the fluid invites infection. We call it sinusitis.
Here is a very good diagram of the ear, nose and throat from the Merck Manual: https://www.merckmanuals.com/home/ear,-nose,-and-throat-disorders/biology-of-the-ears,-nose,-and-throat/introduction-to-biology-of-the-ears,-nose,-and-throat
This is the Ears and Nose Page