Mon Sotah 42

The reason we say the Meshuach Milchama says the "Kohain's part" and not the Sgan, because we compare him to Shoter." Just as the Shoter is appointed, yet he has someone appointed above him, so toot he Kohain. The Sagan is not appointed.
'
Tosfos asks: that is Sanhedrin we call the Sagan the appointed one?

Tosfos answers: he was appointed to the office that theBais hamikdash's adminstration created. This is similar to many positions they made up to have there, like a treasurer. However, it wasn't a position that the Torah authorized.