The kortholt is essentially a folded cornamuse. The bore doubles back on itself to give an instrument with a "musical" length twice its actual length. Apart from the obvious advantage of compactness there is a further benefit. This is that some additional fingerholes can be drilled for the "upward" bore to provide some extra notes below the normal range. The fingering becomes slightly tricky requiring the use of all ten digits plus the joints of the two index fingers. However, a tenor instrument can have its range extended down from "c" to "F" and a bass from "F" to "BBflat".    

The instrument shown is a tenor kortholt constructed from bubinga.