appendage vs appendix

appendage

noun
  • A natural prolongation or projection from a part of any organism. 

  • A part that is joined to something larger. 

  • An external body part that projects from the body. 

appendix

noun
  • Any process, prolongation, or projection. 

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

  • The vermiform appendix. 

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