oral cavity vs orifice

oral cavity

noun
  • The cavity of the mouth, especially the part of the mouth behind the gums and teeth that is bounded above by the hard and soft palates and below by the tongue and by the mucous membrane connecting it with the inner part of the mandible. 

  • The hollow on the lower surface of the head from which the proboscis protrudes. 

orifice

noun
  • A mouth or aperture, such as of a tube, pipe, etc.; an opening. 

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