Examples from literature

• Cells belonging to the epithelium. 
• Its surface is at first smooth and shiny, but as necrosis of the tissue elements takes place in the centre, it becomes concave, and in many cases the epithelium is shed, and an ulcer is formed. 
• The cells composing the columns and filling the alveoli vary with the character of the epithelium in which the cancer originates. 
• The middle layer, on the contrary, forms nerves and muscles, vessels and connective tissue, and little or no epithelium. 
• They are distributed through every tissue of the body, except the epidermis and its products, the epithelium, the cartilages, and the substance of the teeth.