jungle gym vs monkey bars

jungle gym

noun
  • A play structure designed for children to climb on, traditionally constructed as a frame of metal bars as introduced in 1920. 

monkey bars

noun
  • A row of bars, found on playgrounds, under which one hangs by the arms and crosses by brachiation (swinging between bars, legs dangling down). 

  • A jungle gym. 

How often have the words jungle gym and monkey bars occurred in a corpus of books? (source: Google Ngram Viewer )