appendix vs proem

appendix

noun
  • A text added to the end of a book or an article, containing additional information. 

  • Any process, prolongation, or projection. 

  • The vermiform appendix. 

proem

noun
  • An introduction, preface or preamble. 

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