Technically, the saddle bow (which can be one word or two) is the curve at the front of the English saddle which, these days, is a very small "loop" over the withers.
Older saddles, though, had a much more pronounced bow - which evolved into the western horn. Medieval falconers would often use a saddle bow designed to provide a perch for the bird, either to free their hands or to carry heavy birds such as eagles longer distances.
(OOC: I am looking into the broken pictures. I think I'm having an issue with Picasa).