Round window: A membrane on the cochlea separating the inner ear and middle ear. The tympanum (eardrum) separates the middle ear and outer ear, also known as the ear canal. QUESTION What causes tooth decay? See Answer From Healthy Resources 10 Rheumatoid Arthritis SymptomsWhat Is Exocrine Pancreatic Insufficiency? Featured Centers Good and Bad Foods for PsoriasisVideo: Getting Personal on Life With MS Health Solutions From Our Sponsors Shot-Free MS Treatment Your Child and COVID-19