BOOK IV. 



PART I. 



Organs of Mastication and Deglutition. 

 CHAPTER I. 



OF THE MOUTH. 



THE Mouth (Cavum Oris) occupies the space in the inferior 

 part of the face, between the upper and the lower jaw. It is 

 separated from the nose by the palatine processes of the supe- 

 rior maxillary and palate bones, and by the soft palate, which 

 is continued backwards from them. It extends from the lips, 

 in front, to the soft palate and pharynx behind, and its floor is 

 formed by the mylo-hyoid muscles. 



The anterior and lateral periphery of the mouth is constituted 

 by the muscles of the lips and cheeks, covered externally by 

 common skin, and internally by the lining membrane of the 

 mouth. The cavity of the latter is divided into two portions, 

 by the projection of the teeth and of the alveolar processes of 

 the upper and under jaws; these two portions, when the teeth 

 are complete, are separated from each other while the mouth 

 is closed. The anterior portion, which is sometimes called the 

 vestibule of the mouth, varies its size very considerably in 

 mastication, and has its parietes extremely moveable. The ca- 

 paciousness of the posterior admits also of much change, by the 

 motions of the tongue and by. the depression of the lower jaw. 



The whole cavity of the mouth is lined by a membrane, con- 

 tinued over the lips from the skin, and, in many respects, strong- 

 ly resembling the texture of the latter; it is, however, much 



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