Color enhanced transmission electron micrograph showing section of ileum, microvilli, mucus on surface wall. Magnification 200,000x. Microvilli, any of the small, fingerlike projections of the surface of an epithelial cell. Epithelium, any animal tissue that covers a surface, or lines a cavity or the like, and that, in addition, performs any of various secretory, transporting, or regulatory functions. Ileum, the third and lowest division of the small intestine, extending from the jejunum to the cecum.