Where is gtkmm.h (or am I going mad)?

[Alan Mazer <alan judy jpl nasa gov>]

A few months ago, or maybe a little past that, I had an application 
coded using gtmkk for RHEL 6.  I just went back to it now and can't get 
it to compile.  Somehow gtkmm.h seems to have disappeared from my 
system.  More to the point, I can't figure out how to get it back.  I've 
got binaries but no includes.  Yum says that there's nothing available 
except gtkmm24.x86_64 and says that I already have the latest version of 
THAT.  I found an rpm somewhere and tried to install that and just got 
an error.  Am I going mad?  How do I get my gtkmm stuff working again on 
RHEL 6???

-- Alan