This one probably doesn't fit the definition of a folk song (whatever that is), but it has been chanted by generations of med students to remember the names of the cranial nerves. Unfortunately, I only know the clean version. Maybe someone can help with the other, more popular version.

On old Olympus's topmost top, a Finn and German valtz and hop.

The first letter of each word is also the first letter of the name of a cranial nerve.

Pauline