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# Long description

A schematic illustration demonstrates the general structure of the small intestine composed of 4 histological layers. The cylindrical concentric layers are extended out to reveal the histological layers of the small intestine. The small intestine has longitudinal and circular muscle layers, present beneath the outermost serosa layer. The lumen of the small intestine is enclosed by submucosa and innermost mucosa. The blood vessels serving the small intestine supply blood to all the histological layers. The internal surface of the mucosa has circular folds (plicae circulares). There are numerous finger-like projections in the circular folds labelled ‘villi’.