So....today I was discussing some things with a class mate of mine and we were talking about working out the abs. Now for a VERY long time I was, too, under the impression that there was an upper abs and lower abs. It only took a few classes in an anatomy course to get to the topic of the muscular system and that the abdominis rectus is only 1 large muscle, with an insertion at the sternum and an origin at the pubis........but there still remains a question...

I am only 9-10% body fat. My upper abs are pretty prominant, they stick out very much and can ridges between the portions of the muscle can be palpated easily. There is no doubt that my abs are strong and I am low in body fat. However, why do my lower abs still receed into nothingness? I have what appears to be a 4 pack. Here is a link to a picture:
http://www.rit.edu/~cvs5384/pict0020.jpg
It looks like I have 4 prominant muscles in the upper abs, but the lower abs are flat. I do crunches to maintain and build the abs and used to do reverse crunches for "lower abs" (which i now know is BS). My crunches should be enough, but is there any way to make the lower abs show through for the 6/8 pack effect? The Rectus Abdominis is seperated into 2 columns of 4 muscles, so why arent they showing through as an 8 pack or even 6 pack when I have such a low percentage of body fat? Is there any way to change this? You can't spot lose fat and you can't gain muscle in just one part of a muscle.....the whole muscle contracts as a whole...so whats the verdict?