DIGESTION 97 



little beside salt and a weak ferment. It serves to moisten 

 the food as it is being crushed by the molar teeth. The sub- 

 maxillary and sublingual secretions contain, in addition to the 

 ferment, ptyalin, mucus which the tongue mixes with the 

 masticated food as it forms it into a bolus suitable for swallow- 

 ing. The dorsal surface of the tongue is covered by papillae, 

 which rasp the food against the palate. Of these the greater 

 number are pointed, or filiform. The remainder are flat-topped, 

 or fungiform. The two varieties may be distinguished with a 

 lens, especially on the sides of the tongue. Usually the fungi- 

 form papillae are the redder. In fever, when the tongue is 

 densely furred, they stand out as bright red spots. The back 

 of the tongue is crossed by a V-shaped row of papillae of larger 

 size, each surrounded by a slight fossa and a vallum, and hence 

 termed " circumvallate." Very minute organs of sense 

 taste-bulbs stud the mucous membrane which lines the fosse. 



The hard palate ends in a muscular curtain the soft palate 

 the central portion of which the uvula depends lower than 

 the rest. On either side the soft palate splits into two folds ; 

 the anterior, continued to the side of the tongue ; the posterior, 

 to the pharynx. 'These folds, since they bound the gateway 

 into the pharynx, which is known as the " fauces," are termed 

 the " pillars of the fauces." The tonsil lies between the 

 anterior and posterior pillars of the fauces, but does not appear 

 as a prominence unless inflamed or enlarged. 



The pharynx hangs as a bag from the base of the skull. It, 

 like all the rest of the alimentary tract, is lined by mucous 

 membrane. " Mucous membrane " is not a happy term. It 

 does not denote that the epithelium secretes mucus. It may or 

 may not possess this property. Nor does it imply that it has 

 a different origin from the skin that it arises from hypoblast, 

 the inner layer of the rudiment from which the embryo grows. 

 The term is applied to all internal, and therefore moist, 

 surfaces, whether they arise from hypoblast, as in the case 

 of the lining of the greater part of the alimentary tract, or 

 whether they are involutions of epiblast as in the case of 

 the mouth and also of the extreme lower end of the alimentary 

 tract. Almost the whole of the alimentary canal is, in the 

 first instance, a tubular cavity in the interior of the embryo, 

 lined by hypoblast. This cavity communicates with the 



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