Sandi, the anatomy and functioning of the horse's hyoid apparatus and tongue are gone into in complete detail in the DVD set ("The Anatomy of Bitting") that Dave Elliott and I produced, and which is available for sale through this website -- go to the Home Page and click on the link.
Briefly, the reason that you should never allow anyone to restrain a horse by means of his tongue is that a hard enough pull on the tongue can evert the small joints of the hyoid chain. This hard a pull can only be effected with a dry hand or a dry glove firmly pulling the tongue down and to the side. This technique of restraint is, in fact, still taught in some veterinary colleges and this is extremely unfortunate; no one should ever use it, and in this day and age of "chemical restraint" it is really never needed. The same may be said for ear-twitching -- it should never be done, and it is not needed.
I am moved to ask why you ask this particular question. Has someone recently so roughly handled your horse? Or was your interest more from the side of just wanting to know the anatomy? -- Dr. Deb
Thank you for your prompt answer. On a group I am on we are talking about equine dentistry and the mention of tongue holding caught my eye and I remember you talking about the danger of that and the hyoid bones. Been only about 7 years ago, so I wasn't too clear on why not other then it was a bad thing for those little bones. Knowing things like that and being able to convey them to others might help our majestic friends And no, nobody has tried that on my guy, I know better then to let it happen! I plan on purchasing all those dvds by the way. Thanks again. Sandi