mentum vs piehole

mentum

noun
  • The chin. 

  • The central part of the labium in insects. 

  • A chin-like projection below the mouth of certain mollusks. 

  • A projection in front of the flower in some orchids. 

piehole

noun
  • A person's mouth. 

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