File:Anatomy, physiology and hygiene (1900) (14592651727).jpg

Identifier: anatomyphysiolog00walk (find matches)
Title: Anatomy, physiology and hygiene
Year: 1900 (1900s)
Authors: Walker, Jerome, 1845-
Subjects: Physiology Health
Publisher: Boston, Allyn and Bacon
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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se roots and cause 1 From various causes, such as sickness, hereditary peculiarities, orlack of proper tooth-forming food, the appearance of the teeth may bedelayed till one year of age, or even longer. Babies are sometimes bornwith teeth. 2 The first permanent teeth appear behind the posterior milk molars,before any of the milk teeth are shed, viz., at six years, so that a childof six has twenty-four teeth, —twenty temporary and four permanent. DIGESTION. 125 their absorption, the temporary teeth being eventuallyshed as little conical crowns, with convex bases. Teeth are classified as ificisors, canines, bicuspids, andmolars. In the first or temporary set, there are in eachjaw four incisors, two canines, and four molars. In thesecond or permanent set, there are in each jaw the samenumber of incisors and canines, four bicuspids, and sixmolars. The bicuspids 1 replace the molars of the tempo-rary set. The teeth of the permanent set are larger andmuch stronger than those of the first.
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Fig. 57.Section of Jaws, showing the Temporary and Permanent Teeth. The incisors, or cutters, are in the front of each jaw,and have chisel-like edges for use in cutting or biting food.Adjoining the incisors are the canines,2 which are some- 1So called, because they have two cusps or points upon their crowns.2 The upper canines are sometimes called eye tooth, the lower onesstomach teeth, though they have no peculiar relation to these organs. 126 DIGESTION. what pointed at the edges, like the teeth of dogs. Theyassist the incisors in dividing the food. The bicuspidsare between the canines and molars. They are shorterand thicker than the canines, and assist the molars incrushing the food. The remaining teeth are the molars,1or grinders. These teeth pulverize the food, and areespecially adapted for the purpose, their grinding sur-faces being broad and irregular. This grinding actionis effected by the pressure of the lower jaw against thestationary upper jaw, with lateral, rotary, and upwa

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