(A note on a single ledger line, but not above or below it, is common in 16th-century notation.)(1)
If Palestrina had notated his polyphonic setting in normal clefs, keeping the tenor's reciting note on c', the tenor's a' would have been above the first ledger line over the staff; similarly, the cantus, whose highest note is g", and the altus, whose highest note is c", would have had to utilize a ledger line in the same fashion.
Thus, we find Palestrina and others notating their first-tone Magnificats in chiavette, since the topmost notes, often reaching g" in the cantus, c" in the altus, a' in the tenor, and d' in the bassus, would each have been above a single ledger line in normal clefs.
Since the highest note of the cantus is f", the cantus part can be accommodated with the [C.sub.1] clef, the f" appearing on the single ledger line above the staff.