Bits & Sucking Tongue Back

["Pamela M. Corley" <pcorley@hsc.usc.edu>]

What would you recommend for a horse who sucks his tongue back?  He pulls
it back to where there is only 1/4-1/2" visible in front of the bit.
What causes this?  What would you recommend to change this?  

I get the impression that bitting is often a matter of personal preference
& experience of the trainer, as well as one of trial and error.  I would
like to learn enough to be able to judge whether the approaches being
tried will be successful.

I found some books on bits/bitting that may help me:
	Edwards, Elwyn Hartley "Bitting: In Theory & Practice"
	Langdon, William G. "Bits and Bitting Manual"
	Roberts, Tom "Horse Control and the Bit"
Is anyone familiar with these or other books?

Thanks for your assistance either on the listserv or offline.

Pamela Corley
pcorley@hsc.usc.edu