The wall of the alimentary canal is made up of four basic layers. First, there is serosa, which is a thin membranous covering around the oesophagus. Then, there is a muscle layer-outer layer of longitudinal muscles and an inner layer of circular muscles. These two layers constitute the muscularis. Last, there is the submucosa, which contains a few oesophageal glands. Then comes mucosa, which has several layers of flattened cells.