The bulge is part of the die crack. Only it's a break in the die or a piece out of the die. It shows up as the opposite on the coin or raised metal.
The only coin with a bigger or more die cracks is my Broas Pie Bakers CWT . Definitely the biggest I've seen on a small US coin .
Well, when I clicked on this thread I was expecting pictures of some 21 morgans. I was tricked! Nice 3 center. I have an 81 with a "pre" cud in that same area but yours is much more advanced