The shirt I am wearing today is one I bought many years ago. It's a Van Heuson, a brand which may not even be around these days; it's so long since I bought a shirt that I really have no idea what shirt-makers still exist. I suppose there is still M&S, although Bhs, their main competitor, has gone to the wall. Anyway, Van Heuson was a brand just a cut above the common or garden shirt-makers. So much so that the sleeves have no buttons at the cuffs; they sport double cuffs which should be folded back and held together by cuff links. I wonder, does anyone other than the Prince of Wales use cuff links these days? I always did - provided my shirt cuffs had the necessary holes, even if the cuffs didn't require folding back!
But the point I am getting to - at long last! you exclaim - is that the button holes down the front are vertical, like this | except for the top one (which I can longer fasten) and the bottom one, which is horizontal, like this - .
There seems to be no common reason why this is so. Some say it is because the shirt was at one time buttoned to the trousers, other because the stress on that button is most likely to be horizontal and making the button hole horizontal means there is less stress on the cotton used to secure the button. I guess I shall never know!