

CHAPTER VI 



DIGESTION 



The Canal. The prospect presented by a widely open 

 mouth is too familiar to need description, but a few details 

 may be pointed out. The teeth are, or should be, thirty-two 

 in number. Starting from the middle line of either jaw, the 

 two first are incisors, with chisel-shaped cutting edges. If they 

 meet, as they ought to do, their edges are ground flat. The 

 third tooth is the canine, with a more or less pyramidal crown. 

 Then two premolars, or " milk-molars," as they are often 

 termed, because they are the only grinding teeth of the first 

 dentition. Twenty is the full complement of teeth in a child. 

 Lastly, three strong grinders the molar teeth. The third 

 molar, or wisdom-tooth, is evidently disappearing in the human 

 race. In civilized people, whose brains are large and jaws small, 

 it does not appear until about the twentieth year. Sometimes 

 it tries to squeeze through the gum of a jaw not large enough 

 to carry it, and causes trouble by becoming " impacted " 

 beneath the ascending ramus. Not infrequently it fails to 

 appear. It may be truly said that the increasing wisdom of the 

 human race is responsible for the postponement of its develop- 

 ment, although this is hardly the circumstance to which it 

 owes its name. A fold of mucous membrane the frenulum 

 linguse connects the under side of the tongue with the floor 

 of the mouth. On either side of this may be seen the opening 

 of a duct common to the submaxillary and sublingual salivary 

 glands. The opening of the duct of the parotid gland is not 

 so easy to find. It pierces the mucous membrane of the cheek 

 opposite to the base of the second molar tooth of the upper 

 jaw. The parotid gland lies just below the ear, behind the 

 jaw. The saliva which it secretes is a watery fluid containing 



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