CHAPTER VII 

 MASTICATION, INSALIVATION AND DEGLUTITION 



Physiological anatomy of the organs of mastication The teeth Enamel of the teeth 

 Dentin Cement Pulp-cavity Superior maxillary bones Inferior maxilla Tem- 

 poro-maxillary articulation Muscles of mastication Saliva Parotid saliva Sub- 

 maxillary saliva Sublingual saliva Secretions from the smaller glands of the mouth, 



tongue and pharynx Mixed saliva General properties and composition of the saliva 



Uses of the saliva Deglutition Mechanism of deglutition Protection of the poste- 

 rior nares during the second period of deglutition Protection of the opening of the 

 larynx and uses of the epiglottis in deglutition. 



INORGANIC alimentary substances, with few exceptions, are introduced 

 in the form in which they exist in the blood and require no preparation 

 or change before they are absorbed ; but organic nitrogenous substances 

 are always associated with more or less matter possessing no nutritive 

 properties, from which they must be separated ; and even when pure, 

 they undergo certain changes before they are taken up by the blood. 

 The non-nitrogenous matters also undergo changes in constitution or 

 in form preparatory to absorption. 



MASTICATION 



In order that digestion may take place in a perfectly natural manner, 

 it is necessary that the food, as it is received into the stomach, should 

 be so far comminuted and incorporated with the liquids of the mouth 

 as to be readily acted on by the gastric juice ; otherwise, gastric diges- 

 tion is prolonged and difficult. 



Physiological Anatomy of the Organs of Mastication. In the adult, 

 each jaw is provided with sixteen teeth, all being about equally 

 developed. The canines, so largely developed in the carnivora but 

 rudimentary in the herbivora, and the incisors and molars, so fully 

 developed in the herbivora, are, in man, of nearly the same length. 

 Each tooth presents for anatomical description a crown, a neck and a 

 root. The crown is the portion not covered by the gums ; the root is 

 the portion embedded in the alveolar cavities of the maxillary bones ; 

 and the neck is the portion, sometimes slightly constricted, between the 

 crown and the root and covered by the edge of the gum. Each tooth 

 presents on section several distinct structures. 



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