Japanese matchlock Teppo

[rickystl]

While on this subject, this might be a good time to pose a question about these Teppo's that is still a mystery to me. That being the design of the front and rear sights. Especially the rear.

First the rear site: On the top there is a very thin slot with a partially drilled hole. On the side there is a hole that runs horizontal through the width of the sight. This one horizontal hole seems to be common on every Teppo I've seen.

Front sight: Again, a partially drilled vertical hole (like the rear sight) is present, along with a slot.

It seems that both sights were designed for some type of additional attachements. But I have no idea what it would be. Any ideas about this?

Here are pics of the rear sight: