eardrum vs middle ear

eardrum

noun
  • A thin membrane that separates the outer ear from the middle ear and transmits sound from the air to the malleus. 

middle ear

noun
  • The cavity in the temporal bone between the eardrum and the inner ear that contains the ossicles, and which conveys sound to the cochlea. 

How often have the words eardrum and middle ear occurred in a corpus of books? (source: Google Ngram Viewer )