The wall of alimentary canal from oesophagus to rectum possesses four layers namely serosa, muscularis, sub-mucosa and mucosa.
i. Serosa is the outermost layer and is made up of a thin mesothelium or the epithelium of visceral organs and has some aconnective tissues.
ii. Muscularis is formed by smooth muscles usually arranged into an inner circular and an outer longitudinal layer. An oblique muscle layer
may be present in some regions.
iii. The submucosal layer is formed of loose connective tissues containing nerves, blood and lymph vessels. It is highly vascular, dense connective tissue. In duodenum, glands are also present in
iv. Mucosa is the innermost lining. This layer forms irregular folds (rugae) in the stomach and small finger-like foldings called villi in the small intestine