I submit this image to help disambiguate if the trigger was on the top or the bottom. This is a fairly poor image that Matt Jefferies drew to have his design fabricated. A higher quality image of this shows up in the book Star Trek Sketchbook
and I've annotated this version of it to make known the illegible writing.
Franz Joseph based his drawings (and his assumptions) on the photos which appear in the book The Making of Star Trek
, and you can see where he got it wrong.