extremity vs index finger

extremity

noun
  • A hand or foot. 

  • The most extreme or furthest point of something. 

  • A limb (“major appendage of a human or animal such as an arm, leg, or wing”). 

  • An extreme measure. 

index finger

noun
  • the forefinger 

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