The wall of alimentary canal consists of four basic layers. From the outer surface inwards to the lumen, the layers arc as follows - visceral peritoneum (serosa), muscularis (muscular coat), submucosa and mucosa (mucous membrane). Mucosa is the innermost layer lining the lumen of the alimentary canal. It is so named because it secretes mucus to lubricate the inner lining of the gut. It is further composed of three layers — muscularis mucosa, lamina propria and epithelium.