Light micrograph of a transverse section through a lingual tonsil (right), which is located at the base of the tongue (centre and left) at the back of the mouth. The tonsils, part of the immune system, are large lymphatic nodules in a mucous membrane. Each tonsil has a stratified squamous epithelium outer lining (red, right). Beneath it are lymphoid follicles (purple) that contain lymphocyte white blood cells. Mucous glands (left, pale blue) located at the root of tongue drain into the lingual tonsils. Muscles (pink) of the tongue are also seen. Magnification: x20 when printed at 15cm wide.