Rashi on Leviticus 9:20/רש"י על ויקרא ט׳:כ׳

1וישימו את החלבים על החזות AND THEY PUT THE FAT UPON THE BREAST — After the waving the priest who waved them gave them to another priest to burn them; consequently what was previously above was now beneath (cf. Rashi on Leviticus 7:30; Menachot 62a).