Light micrograph of a cross-sectioned ureter stained with haematoxylin and eosin. Lining the lumen is a transitional epithelium, or urothelium, with several layers of cells. Lining the interior is the folded mucosa, with the lamina propria, formed by connective tissue, surrounding it. Surround this are two muscular layers: an inner layer, longitudinally oriented (seen in cross-sectioned) and a very thin circular outer layer oriented transversely to the axis of the ureter. Finally, a very thin adventitia is on the outside.