Hidden inside the top, the bass bar is one of the elegantly sculpted parts of the violin. One day, from curiosity I mapped out how a normal bar, which has a sweeping, scooped look on the contoured violin top, would look if it were on a flat top rather than an arched one, by mapping the heights on a flat line, and was I surprised! It turns out to be a neat triangle with the top lopped off round, and if it went all the way out to the ends including through the top, the very tips of the ends would end right at the ribs.
In this drawing the bar is the cross-hatched area. The ribs and linings are far left and right, and the top is the flat platform between them. The tiny marks where the ends of the bar triangle end represents the position of the purfling on the outside.