Where does canon law state the body must be during a Catholic funeral mass?

On entering the church, and closed coffin ( this is the funeral mass, not a wake or viewing, held earlier) the Coffin enters the church, fore and aft ( front and back) the principal mourner immediately follows the burial vessel- I held this office, so to speak at my mother's funeral mass, then relatives in accordance to relation to the family etc. The coffin goes down the center aisle of the church and is usually placed fore-and-aft again, on the altar structure, usually covered.