The common bile duct transports bile from the liver and gallbladder to the small intestine. (H&E)
The lumen of bile duct has many folds lined with a simple columnar epithelium.
This epithelium is relatively uniform in height, but appears otherwise depending on the angle the section cut through it.
Where the section is cut orthogonal to the surface of the epithelium, a single row of cells is seen.
Where the section is cut tangential to the surface of the epithelium, it passes through adjacent cells resulting in multiple nuclei and extra tall cells. This can be easily confused with a pseudostratified columnar epithelium.