Anatomy, physiology and hygiene . is thrown into ridges. The cells cover-ing the surface of the mucous membrane are epithelial cells, and togetherconstitute the epithelium. Sometimes the mucous membrane is calledthe internal skin, from a similarity to the external skin. 2 Ordinarily, in health, there is just sufficient mucus to act as a lubri-cant. But in some, young children especially, whose tissues are verysensitive, an excess of mucus is readily induced by an irritation oi themucous membrane, through indigestible food, exposure of the skin tosudden changes in temperature, and by o
Anatomy, physiology and hygiene . is thrown into ridges. The cells cover-ing the surface of the mucous membrane are epithelial cells, and togetherconstitute the epithelium. Sometimes the mucous membrane is calledthe internal skin, from a similarity to the external skin. 2 Ordinarily, in health, there is just sufficient mucus to act as a lubri-cant. But in some, young children especially, whose tissues are verysensitive, an excess of mucus is readily induced by an irritation oi themucous membrane, through indigestible food, exposure of the skin tosudden changes in temperature, and by other means. This excess ofmucus may, by coating proper food, interfere with its digestion. On theother hand, if the mucous membrane is not torn, injured, or diseased,such an excess, by coating improper articles that have been swallowed,will generally prevent any injury that might otherwise result fromthem. 114 DIGESTION. 115. The Mouth is the commencement of the canal. Itconsists of the lips in front; a cheek on each side; a bony. Fig. Vertical Section through the Middle of the Pace, Neck, and Upper Vertebrae. 1, Cavity in the skull. 2, opening of left Eustachian tube. 3, the hard palate. 4, the soft palate. 5, muscular wall in front of tonsil. 6, muscular wall behind the tonsil. 7, the left tonsil. S, pharynx, or throat. 9, the epiglottis. 10, the hyoid bone. 11, oesophagus. 12, the cavity of larynx. roof, or hard palate, separating the mouth from the cavityof the nose, or nasal passages ; and the tongue below. In DIGESTION. 115 the back part of the mouth is the soft palate, or cur-tain, that separates the mouth from the pharynx, andwhich is raised in the act of swallowing. The mouthcontains the teeth, and is moistened by the saliva. 116. The Pharynx, or throat, is at the first bend of thealimentary canal downwards. It is, in general, funnel-shaped, with its upper portion,or roof, rounded like a buggy-top. It is slightly constrictedin front, on each side, by twomuscular p
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