1 6 0 . ▁P é rot in ' s ▁works ▁are ▁preserved ▁in ▁this ▁compilation ▁of ▁early ▁poly ph onic ▁church ▁music , ▁which ▁was ▁in ▁the ▁collection ▁of ▁the ▁c athedral ▁of ▁Notre ▁D ame ▁in ▁Paris . ▁The ▁Magn us ▁liber ▁also ▁contains ▁the ▁work ▁of ▁his ▁success ors . ▁In ▁addition ▁to ▁two - part ▁org ana , ▁this ▁book ▁contains ▁three - ▁and ▁four - part ▁compos itions ▁in ▁four ▁distinct ▁forms : ▁org ana , ▁cla us ula e , ▁conduct i ▁and ▁mot ets , ▁and ▁three ▁distinct ▁styles . ▁In ▁the ▁organ um ▁style ▁the ▁upper ▁voices ▁are ▁highly ▁mobile ▁over ▁a ▁ten or ▁voice ▁moving ▁in ▁long ▁un me as ured ▁notes . ▁The ▁disc ant ▁style ▁has ▁the ▁ten or ▁moving ▁in ▁measured ▁notes , ▁but ▁still ▁more ▁slowly ▁than ▁the ▁upper ▁voices . ▁The ▁third ▁style ▁has ▁all ▁voices ▁moving ▁note ▁on ▁note , ▁and ▁is ▁largely ▁limited ▁to ▁conduct us . ▁The ▁surv iving ▁sources ▁all ▁commence ▁with ▁a ▁four - voice ▁organ al ▁setting ▁of ▁the ▁Christmas ▁Grad ual , ▁V ider unt ▁om nes , ▁believed ▁to ▁be ▁P é rot in ' s , ▁as ▁most ▁likely ▁did ▁the ▁original ▁Liber . ▁However , ▁the ▁manuscript s ▁and ▁fragments ▁that ▁surv ive ▁date ▁well ▁into ▁the ▁th ir teenth ▁century , ▁meaning ▁that ▁they ▁are ▁preserved ▁in ▁a ▁form ▁not ated ▁by ▁mus icians ▁working ▁several ▁gener ations ▁following ▁Lé on in ▁and ▁P é rot in .