At the edge of the crystal here there is visible what looks very much like a chip in the edge of the glass. Such chips are common, but that is not what this is.
This is an example of why getting a watch cleaned is a good idea. This bit of glass is certainly not doing this watch any good floating around in there, and could harm something if it got inside.
So where did it come from?
That is a mystery. But you sometimes see things like this when looking really, really closely at things.
grade 82. It's an 18 size, lever-set movement that was made in both 13 and 15 jewel versions. This example was made about 1885.