Make a small incision in the umbilical fold or a short transverse right upper quadrant incision. Reach in, palpate, and deliver the thickened pylorus. Make a longitudinal incision over the anterior surface of the thickened portion. Deepen this incision through the hypertrophied circular fibers. A special spreader assists in opening the myotomy to display the herniated submucosa. Carry the myotomy from the stomach down onto the duodenum, taking care not to injure the mucosa. Perforation is most likely to occur at the duodenal end, because the duodenum is thinner than the stomach. The myotomy must complete divide all fibers of the hypertrophied pylorus.