Illustration of the upper surface of the tongue. The front of the tongue's surface is covered in small projections called papillae. The largest of these, the vallate papillae (8), are easily seen by the naked eye and contain taste buds. At the back of the tongue are the lingual tonsils (10) and either side of the throat are the palatine tonsils (7). The tonsils are collections of lymphoid tissue that are part of the immune system. The epiglottis (2) is a flap of tissue that covers the trachea (windpipe) when eating. Hanging at the top of the throat is the uvula (4). From Traite d'Anatomie Humaine, Vol 3 (1905) by French anatomist Leo Testut (1849-1925).