Wow! Thats one amazing horn. The drawing of the buildings looks quite well done and I think raised the quality above the "Folk Art" realm, though the florals do give it that naive quality.
The artist may have just stopped doing the chip carving at the neck because he changed his mind on what he wanted to do. It looks like the points were done between the scribed arches and he just gave up because it was getting too messy/busy around there. Who knows, but it happens! Its a really beautiful horn, congratulations. It looks to be in a great home now.
Any indication of what period/region?