A villus is a small, hair-like vascularized process on the free surface of a membrane. Example: villi of the small intestine : 20 to 40 villi per mm2 of mucosa. Each villi is a fingerlike projection, 0.5 to 1 mm long, covered by a single layer of columnar epithelium and containing a network of capillaries and a lymphatic vessel called a lacteal.