THE DIGESTIVE TEACT. 589 



The epithelium is continuous with that of the skin, and is 

 stratified; the surface of the lips, however, appears smooth, 

 because the epithelial cover does not follow the curves of the 

 papillary elevations. The same peculiarity is found all over the 

 oral mucosa. The epithelium sends prolongations into the con- 

 nective tissue forming the racemose mucous glands, which, on 

 the inner surfaces of the lips, are very large, and visible to the 

 naked eye. Similar formations are found in the whole mucosa 

 of the oral cavity. 



The mucosa of the oral cavity is thickest on the hard palate, 

 especially its posterior portion, and intimately connected with 

 the subjacent periosteum. Very coarse bundles of fibrous con- 

 nective tissue, blending with the periosteum, compose the gums, 

 on which large papillae are also found. In the floor of the oral 

 cavity the connective tissue is comparatively loose, and the strat- 

 ified epithelial layer thin ; here and on the reduplications of the 

 mucosa (frenulum linguae, arcus glosso-palatinus, etc.) the pap- 

 illae are imperfectly developed. In the epithelial layer of the 

 soft palate and palatine arches bud-like formations are found, 

 similar to those of the circumvallate papillae of the tongue. 

 Many papillae contain terminal nerve-buds (Krause's bulbs), con- 

 nected with medullated nerve-fibers. Such structures are found 

 in larger numbers on the inner surface of the lips, and on the 

 anterior surface of the soft palate. 



(2) The tongue is a bulky mass of striped muscles. Its cover- 

 ing mucosa is smooth on the lower surface, while the upper is 

 abundantly provided with numerous large papillae, and in this 

 situation the stratified epithelial investment follows the papillary 

 curves. Three varieties of papillae are found on the tongue 

 viz. : filiform, fungiform, and circumvallate. 



(a) The filiform papillce, the most abundant, occur over the 

 entire upper and anterior surface of the tongue ; they are long 

 and slender (1-2 mm. in length), and composed of connective 

 tissue, dividing at the apex into a varying number of thread-like 

 offshoots. They are largest in the middle of the upper surface 

 of the tongue, especially toward the location of the circumvallate 

 papillae, while at the point and the lateral borders of the tongue 

 they become smaller. In children they are comparatively much 

 less developed than in adults. The stratified covering epithelium 

 produces hair-like elongations, which are composed of flat, horny 

 epithelial bodies corresponding to the projections of the connect- 

 ive tissue j such projections are wanting in children and on the 



