several layers of muscle and mucous membrane make up the colon wall. Starting with the inside layer and moving outward, they are called the mucosa, muscularis mucosa, submucosa, muscularis propria, subserosa, and serosa. Cancers that start inside the colon and grow outward may grow through all these layers and invade other organs. These same layers are present in most of the intestines (digestive tube). See also colon.