what does 'fojo 37' mean in this marriage record?

when i was looking up the marriage record for marcial banuelos and mariana bonilla, i saw the text 'fojo 37' on the side. what does it mean?

you can see it here

https://familysearch.org/pal:/MM9.3.1/TH-1-18453-66521-57?cc=1874591&wc…

It says "foja 37", which in modern Spanish would be "hoja 37" and in English "sheet 37". In those years many times they numbered the sheets of a book rather than each page. It seems to me they are referring to the 37th sheet of another book (probably the one with the full marriage information including the witnesses statements) rather than to the 37th sheet of that book.

Best,
Victoriano Navarro