nodule vs nodulus

nodule

noun
  • A rounded mass or irregular shape; a little knot or lump. 

nodulus

noun
  • A nodule; a little knot or lump. 

  • The part of the vestibulocerebellum that is at the end of the vermis 

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