[...]rtebantur [...]

These letters match part of the text of the responsory verse 'Per quattuor partes euntes ibant et non revertebantur cum ambularent' (Cantus ID 007699a) which is found on fol. 174v in the P-BRs Ms. 28 sung at Vespers for Matthaei (see http://pemdatabase.eu/musical-item/20885). Unfortunately, the musical comparison of the fragment and Ms. 28 showed only partial correspondence between the two sources. Additionally, the text '...umque corpus...' and the music we can read in the responsory (Cantus ID 0. 07699) in P-BRs Ms. 28 fol. 174v do not exactly match the words we can read in the previous text line in fragment C 1372 (...oquem eorum...).