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=12504491