Sheet music became commonplace in homes starting about 1840. Postcards came along some years later, but when the songwriters put their pens to a score postcards and music were a perfect match.
Fingers and toes. We have them and they are a much larger part of life then we think. Every day we use these tiny little digits that are attached to our hands and feet for activities that are uniquely human. Postcards remind us of only a few things we do with fingers and toes.