Mark,
Good work, late to the party, but ahhh, how about extending the 'previous/ next' selector area to be full height of any said graphic being viewed? 
A la HIG/ GUI "Designing Web Usability: The Practice of Simplicity" ; to the effect of 'the active area should be larger than the graphic depicting direction (arrows)' to be 'natural' and easy to use.
Thanks
davew