Middle picture here looks like yolk?
The chick is supposed to finish absorbing before it is ready to leave (search byc for unabsorbed yolk to see the FAQ, it haooens to everyone)
My best (read poor, at best) guess is that for some reason it pipped internally before it was done absorbing. Sometimes they even hatch, sometimes people help them hatch...this one just hung out until there was no oxygen left.