Light micrograph of a section through a palatine tonsil. The tonsils, part of the immune system, are large lymphatic nodules in a mucous membrane. The palatine tonsils are located either side at the back of the mouth. Each tonsil has a stratified squamous epithelium outer lining (red, top). Beneath it are mucous glands (pale blue) embedded in connective tissue (darker blue) and lymphoid follicles (purple) that contain lymphocyte white blood cells. Two calcified masses (light purple) are seen at bottom. Magnification: x40 when printed at 15cm tall.