Your arm on the screen is facing the wrong direction (I think). The texture on the back of my guys arm is different from the rest of it so it was easy for me to tell once Notch added skins for your arm (thanks!).
Here's what I mean:
(The last image is what I think the arm would be like if it where a real arm...)
umm. ive messed with the .jar and ive seen that he has already put in volume. the arm part of the skin has been changed too. sorry notch! we cant see the volume yet though because we can see our self anyway. well i cant be sure about the volume part but the skin section (of the volume) was definetly there.