236 



HISTOLOGY 



is generally smooth, but its under surface is indented by many connective 

 tissue papillae, which are particularly long and slender in the gums and 

 lips (Fig. 226). At the inner border of the lips at birth, there are free 

 papillary projections described as "true villi," but these later disappear. 

 Cilia are found on the oral, pharyngeal and oesophageal epithelia in the 

 embryo, but in the adult cilia persist only in certain parts of the pharynx. 



The tunica propria in the mouth, as is generally the case in the digestive 

 tract, has few elastic fibers. Some of its tissue is reticular, and in it, 

 lymphoid accumulations are frequent; they may extend into the sub- 

 mucosa. On the oral surface of the soft palate there is a layer of elastic 



Oblique sec- 

 tions of papillae. 



Hair shafts 

 -7 and sebaceous 

 "' glands. 



Artery. 



Bulb of a hair. 



Submucosa. Orbicular Mimetic 

 muscle. muscle. 



Corium. Epidermis. 



Epithelium. Tunica 

 propria. 



FIG. 226. VERTICAL SECTION THROUGH THB LOWER LIP OF A MAN OF NINETEEN YEARS. X 10. 

 Epidermis and corium constitute the skin; epithelium, t. propria, and submucosa form the oral 



mucous membrane. 



tissue between the propria and submucosa. A similar layer is found in the 

 cesophageal end of the pharynx. It increases in thickness upward, at the 

 expense of the submucosa, so that it forms a thick layer in the back of the 

 pharynx in contact with the muscles, among the fibers of which it sends 

 prolongations. This elastic layer, as the fascia pharyngobasilaris, is at- 

 tached to the base of the skull. 



In most of the oral region there is no sharp line of separation between 

 the propria and the submucosa. The latter may be a loose layer contain- 

 ing fat, and allowing considerable movement of the mucosa, or, as in the 

 gums and hard palate, it may be a dense layer binding the membrane 

 closely to the periosteum. In the submucosa are the branches of various 

 glands. On the inner border of the lips and the inner surface of the cheek, 



