Never seen anything like them before. The braiding looks like a combination of the same skin that is used on the horn and maybe a rawhide of some sort. The skin looks like it came from a reptile of some sort.
Tim
"Made entirely of natural materials, these two matching large powder horns are a real antique and rarity. The body is made of wood and horn and is artfully decorated with leather. Many decades ago, a hunter once transported his gunpowder in it, possibly that it is also pure decoration exhibits. As a lover of special pieces, you will surely enjoy these unique pieces."