Originally Posted by Palomine
And the palate is the roof of the mouth, not the floor of it.
Horses will generally go just fine in many bits, not just those associated with the breed or the way they are shown.
You are right, the palate is the top, I should simply say bottom of the mouth.
Horses in general are very sensitive to bits, more so than most folks think. Especially those that pinch their tongue, or exert a lot of pressure on the bars of the mouth. With some horses the most severe bit you can use is a simple snaffle, why, because their may be no room for their tongue. Many, many behavioral problems are blamed on everything else, when the real problem is the bit, the teeth, the mouth in general.
Breed has nothing to do with how a bit fits. Bit fitting is like saddle fitting, it's the individual horse, not the breed.