The host volume is a Psalterium feriatum, with antiphons and hymns, written in 1545 (colophon f. 102v) by the organist and calligrapher Fridolin Sicher (1490-1546). Other scribes added to the Psalter after 1545. At some point, ff. 145-149, (by Sicher) were removed.
One of these removed leaves, f. 149, is used as the rear pastedown; another fragment was glued half under the front pastedown; the current ff. I-II were attached to the fragment, and the exposed part was trimmed to a strip (V3).
(Sandy Maillard, Fragmentarium, 2018, using material from Franziska Schnoor, M.A., Stiftsbibliothek St. Gallen and Beat Matthias von Scarpatetti.)