In man the mouth cavity, and all internal surfaces of the food tube, are lined with a _mucous membrane_. The _mucus_ secreted from gland cells in this lining makes a slippery surface so that the food may slip down easily. The roof of the mouth is formed in front by a plate of bone called the _hard palate_, and a softer continuation to the back of the mouth, the _soft palate_. These separate the nose cavity from that of the mouth proper. The part of the space back of the soft palate is called the _pharynx_, or throat cavity. From the pharynx lead off the _gullet_ and _windpipe_, the former back of the latter. The lower part of the mouth cavity is occupied by a muscular tongue. Examination of its surface with a looking-glass shows it to be almost covered in places by tiny projections called _papillae_. These papillae contain organs known as _taste buds_, the sensory endings of which determine the taste of substances. The tongue is used in moving food about in the mouth, and in starting it on its way to the gullet; it also plays an important part in speaking. [Illustration: I. Teeth of the upper jaw, from below. _1, 2_, incisors; _3_, canine; _4, 5_, premolars; _6, 7, 8_, molars. II. longitudinal section of a tooth. _E_, enamel; _D_, dentine; _C_, cement; _P_, pulp cavity.] The Teeth.--In man the teeth, unlike those of the frog, are used in the mechanical preparation of the food for digestion. Instead of holding prey, they crush, grind, or tear food so that more surface may be given for the action of the digestive fluids. The teeth of man are divided, according to their functions, into four groups. In the center of both the upper and lower jaw in front are found eight teeth with chisel-like edges, four in each jaw; these are the _incisors_, or cutting teeth. Next is found a single tooth on each side (four in all); these have rather sharp points and are called the _canines_. Then come two teeth on each side, eight in all, called _premolars_. Lastly, the _flat-top molars_, or grinding teeth, of which there are six in each jaw. Food is caught between irregular projections on the surface of the molars and crushed to a pulpy mass. Hygiene of the Mouth.--Food should simply be chewed and relished, with no thought of swallowing. There should be no more effort to prevent than to force swallowing. It will be found that if you attend only to the agreeable task of extracting the flavors of your food, Nature will take care of the swallowing, and this will become, like breathing, involuntary. The instinct by which most people eat is perverted through the "hurry habit" and the use of abnormal foods. Thorough mastication takes time, and therefore one must not feel hurried at meals if the best results are to be secured. The stopping point for eating should be at the _earliest_ moment after one is really satisfied.