And, Clanad, Latin fans might like to know that the noun vicis,in a sense, doesn't exist. That is, 'vicis' does not exist in the nominative case, singular .It exists only in the genitive, the accusative and the ablative, singular and the nominative,accusative, dative and ablative, plural !.It's not found in the genitive in pre-Augustine times. [ So noted in Lewis and Short, A Latin Dictionary] Presumably the idea was that one person, the subject, could not be 'in turn/ in reciprocal succession' with himself, but who knows?.
There are times when Latin is even weirder than it first appears.