first finger vs trigger finger

first finger

noun

  • thumb 

  • index finger 

trigger finger

noun

  • the forefinger 

  • a finger used in pulling the trigger of a firearm 

  • difficulty encountered in finger flexion or extension caused by the narrowing of the sheath that surrounds that finger's tendon 

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