Slide DMS030. [mesentery, rat; flat mount, silver stain]. With careful focusing, the irregular outlines of the plate-like mesothelial cells (simple squamous) covering the surface of the mesentery may be discerned. Deeper focusing may give optical sections of blood capillaries in the mesentery and reveal the outlines of the simple squamous cells constituting their endothelial lining. (Note: endothelium will be studied in more detail when the cardiovascular system is discussed.)