144 



NORMAL HISTOLOGY. 



CHAPTER X. 



THE DIGESTIVE TRACT. 

 THE MOUTH. 



THE mucous membrane of the oral cavity consists of the epi- 

 thelial covering and the connective-tissue stroma or tunica propria ; 

 the deeper layers of the latter fade insensibly into the subjacent 

 tissues which unite the mucous membrane with the surrounding 

 deeper parts. The epithelium lining the entire oral cavity is of 

 the stratified squamous variety, continuous with the epidermis on 

 the one hand and with the covering of the pharynx on the other. 

 The tunica propria is composed of interlacing bundles of fibrous 



connective tissue containing elastic net- 

 works, and possesses numerous simple 

 papillae which encroach on the epithelial 

 layer, but do not appear on the free 

 surface of the mucous membrane. The 

 latter is broken in many places by the 

 openings of the ducts of the numerous 

 glands which occupy the submucosa 

 and deeper parts of the mucosa. . 



In the transition of the skin on the 

 lips, where the skin passes into the 

 mucous membrane, the epithelium is 

 greatly thickened, while the connective- 

 tissue layer decreases in thickness ; the 

 subepithelial papillae here become very 

 prominent. The hair-follicles disappear, 

 but the sebaceous glands still are present, 

 especially near the angles of the mouth and in the upper lip. The 

 mucous membrane covering the cheeks adheres tightly to the bucci- 

 nator muscle, and possesses small papillae ; that covering the gums 

 is dense, and contains numerous well-marked papillae beneath the 

 epithelium, the submucous tissue being closely united with the peri- 

 osteum. The portion covering the hard palate is thin and firmly 

 united to the periosteum, while that investing the soft palate, the 

 uvula, and the fauces is much thicker, less dense, possesses numerous 

 mucous glands, and, in many places, is so densely crowded with lym- 

 phoid cells that the entire mucous membrane assumes the appearance 

 of adenoid tissue. 



Section of oral mucous membrane of 

 child ; the surface of the fibrous tunica 

 propria is broken by minute papillae, 

 which contain the endings of the blood- 

 vessels and the nerves. The papillae 

 are covered by the stratified squamous 

 epithelium. 



