I'm guessing that the "metal spikes" were part of a latching mechanism intended to bind the back cover to the front. Obviously, but not surprisingly, the other half of the mechanism is missing after these many years. This reminds me of the latching mechanism on my family Bible from the late 19th century. - similarly with "spikes" but again missing the other half of the latches.
There are at least 2 Graduales published by de la Roche on Google Books, both for the diocese of Lyon (Lugdunensis), dated 1771 and 1780. But I suspect your Graduale is not for the Lyon usage because the melody and text for the Introit for the 1st Sunday of Advent in one of your photos is not the same as the Introit for Lyon.
In the back of the book in the second link, de la Roche has an advertisement for several editions of the Graduale for Lyons. It doesn't surprise me that they would have published editions for other diocese as well.
Thanks to all of you for your helpful comments. I wanted to address them and give you an update on my research into this book.
It is possible, as WGS suggests, that the "metal spikes" on the front were part of a latching mechanism. However, I now believe that they are "bosses," or "brass bosses," which are metal attachments designed to protect the book's binding by preventing it from opening all the way. They were originally on the back cover as well, but perhaps removed because of the annoyance of having a book that won't lay flat on a surface.
WorldCat lists several copies of the 1763 version of this gradual at libraries in Europe. Here is one example: Bibliothèque de Genève
I have yet to find the full text of the 1763 version online, but it seems likely that these will match the one I have.
As for the original location of the book, there is a handwritten note at the front of the gradual which says "Antiphonaire fin 17ème, region Chaumont[,] H[au]te-Marne," indicating that the book is from Chaumont, in the Haute-Marne département, Champagne-Ardennes region. When I posted previously I hadn't figured out what the note said, but it now seems likely that the book is from Chaumont, rather than Guérande. A possible original location would then be the Basilique Saint-Jean-Baptiste de Chaumont, which has a long history, and is home to several similar antiphonals.
If anyone has additional insight about this book, or ideas about how to more precisely identify its origin and history, please let me know. Thanks again for your help.
I would look at Theodore Carp, An Introduction to the Post-Tridentine Mass Proper, 2 vols. (Middleton, Wisc.; American Institute of Musicology, 2005). He lists one Lyon Graduale from 1763. What is so interesting about this book is that it documents that during the whole post-Tridentine period, there was an active cultivation of chant, shown by the proliferation of published graduals. Moreover, they show that the Medicean Gradual published after the Council of Trent was by no means normative.
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