Does anyone Know what the plastic insert is in the base of an American Champion Toilet Model 4260?

[JHO]

I'm in the process of replacing the flow valve in an American Standard Champion Toilet model 4260. After removing the tank, I noticed there is a plastic insert in the throat of the bowl where flow valve connects to it. It doesn't seem to want to be removed without further breakage. Does anyone know what this is and is it essential?

 

[Marlinman]

American Standard "Horn" #738650-400.0070A. It provides a smooth waterway to the bowl and rim. It is essential. Being cracked it will still do what it is intended to do. It can be replaced if needed.