It's a tongue grid, so those who suggested such a thing are quite right. You don't see them much nowadays.
Overchecks are different in that they're attached to the bridle in such a way as to be affected by what they used to call 'bearing reins' (just for Black Beauty fans!) - I don't know what harness racers call them nowadays. Anyway, they prevent the horse lowering it's head, whereas a tongue grid stops the horse getting its tongue over the bit and works whatever the horse's head position.
Really interesting post!