Complex sentence: In the Tridentine Calendar he was commemorated also on each of the following days up to and including 3 January, the Octave of the 27 Decembs abolished by Pope Pius XII in 1955.
Split into simpler sentences: In the Tridentine Calendar he was commemorated also on each of the following days up to and including 3 January, the Octave of the 27 December feast. This Octave was abolished by Pope Pius XII in 1955.