Somewhere after 1900 the razor companies in Solingen (and surely also elsewhere) prdocued so-called security razors. The security razors have been normal straights or adapted versions, on which a protective mantel was mounted, so that the edge of the razor didn't touch the skin. Later on the same system was used for effilier/ thinning razors.
There are several patents for this protective devices and how they were mounted on the razor. Most of them simply have been clamped somehow on the razors spine - so they could be used for each staight. But some special variants required a certain sliding chute near the spine.
So I think that is what you see on your Dorko. Could be wrong though and it might be something else.
Here are some old advertisements showing these security razors:
Attachment 342299
Attachment 342300
Regards Peter