Hernia at the belly button. (see hernia.) The abdominal wall is formed by two sheets of muscle that run along both sides of the abdomen. In normal development, these sheets of muscle fuse together. When the fusion is incomplete or abnormal, part of the bowel can bulge through the space between the muscles at the belly button. As the infant grows, the muscle layers increase and gradually fuse, eliminating the hernia. This is one of the few hernias that often resolves on its own. Occasionally, surgical correction is required.