The topgallant mast has a topgallant stay, which leads forward, and at least one pair of topgallant backstays (maybe two in a big ship), which lead aft and directly down to the channels on the sides of the hull. The topgallant backstays are among the longest lines in the ship.
Stoney's original post correctly named the topgallant shrouds, which are much shorter.
This stuff doesn't really need to be so complicated. The rigging of a sailing ship is made up of several categories of system, which are duplicated (with some variations due to size and location) for each spar. Standing rigging holds up the masts, and running rigging moves the yards, gaffs, and booms in a highly controlled manner to catch the wind and adjust the ship's course and speed. A few lines (e.g., shifting backstaysys) blur the distinction between standing and running rigging slightly. And rigging evolved over the centuries.
There are two good ways to find out how to rig a model. One is to work from a good, detailed drawing. That can be frustrating, because not all rigging details show up clearly in a side view. The other kind of source is a verbal description that explains just how each line leads. To my notion the ideal is a combination of the two. For the Victory. Longridge's Anatomy of Nelson's Ships probably the best guide to rigging. It contains lengthy written explanations along with George Campbell's beautiful plans.
Ive said it before and I'll say it again: the Victory is not a good model on which to start learning rigging. Unfortunately there are few plastic sailing ship kits on the market that do make good newcomer projects. (After all, if we exclude the little tiny ones, the total number of plastic sailing ship kits currently in production can just about be counted on your fingers and toes.)
In the wood realm things are a good deal better. Bluejacket, for instance, has just released a nineteenth-century American revenue cutter that would be an excellent choice for a newcomer who wants to learn how rigging works.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.