The left picture- that is for an oval stove pipe attachment that would then round off and connect to the rest of the pipe. The other isn’t for piping at all. It is for cooking. It probably has an opening in the back for rear venting.
The first picture on the left is of my Splendid Oak #25. I am trying to figure out what the purpose of this hole next to my hand is for and what is supposed to be attached originally. I’m assuming its used to help warm the air, their is a vent on the bottom back which connects to this top hole and the entire thing is separate from the fire pot. I’ve seen several other Splendid Oak #25’s that do not have this function at all (an attached photo on the right for comparison).