THE MOUTH 



331 



a shallow median furrow (Philtrum), the lower a rounded prominence, the chin 

 (Mentum). The inner or oral surface is covered with mucous membrane which is 



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commonly more or less pigmented. The small papillse on this surface show 

 on their summits the openings of the ducts of the labial glands. Small folds of 

 mucous membrane which pass from the lip to the gum represent the frsenula labii 



