Mittens with a top down thumb

A mitten knitted completely knitted top-down, in the round, seamlessly, including the thumb. Just as there are many advantages to working the body of the mitten or sweater top down so there are to the thumb:

1. I want to try my thumb on to make sure the length is right without having to guess whether the next decrease will bring the thumb in too much (I have made more than one pair with thumbs too short that way! -OK maybe that it just me....).
2. I find that decreasing at the top has an unfortunate effect on the integrity of my fabric - too often the tops of thumbs end up a bit holey after a while. Starting with a firm cast on is a much better bet in this regard - not to mention that if you like you can seamlessly cast on the width of the whole thumb in one go to make it even tougher. I provide both options in the pattern.
3. All the knitting on your mitten runs in the same direction, giving a seamless appearance.