The "bellybutton" in the name refers to the shape of the center of the blanket.
It is formed when the plain knit section hits the patterned ridges. I love it as a symbol of a child's connection to the four sets of families that came before him or her, since a new baby is the heart, root, and hope for everyone involved.
If you don't need the symbolism or would really, really prefer a blanket that lies more flat, simply use a provisional cast on to start with 56 sts, and begin working the blanket starting with round 12 in the main section. After the blanket is finished and blocked, see if you can simply pull the stitches together to close the center by running the tail of your cast-on through the provisional stitches.
15.5 sts/4 inches or 15.25 sts/10 cm, in Main Section pattern, after blocking.
1260 yards of Worsted weight
Lara Neel is a knitting, designing, math diva podcaster who is determined to talk with each and every one of you on her show, Math4Knitters: Crafty Living. Drop by her website, http://laraneel.com/ for more information.