236 THE DIGESTIVE ORGANS. 



cornification of the layer analogous to the stratum corneum of the 

 skin is not complete (compare Skin). In the mucous membrane 

 the cells of even the most superficial layers contain nuclei, which, 

 although partly atrophied, still show chromatin, and as a conse- 

 quence are easily demonstrated. 



Beneath the epithelium lies a tissue of mesodermic origin, also 

 belonging to the mucous membrane and known as the mucosa or 

 stratum proprium (lamina propria, tunica propria), in which nu- 

 merous glands are situated. The mucosa consists of a fibrillar 

 connective tissue with few elastic fibers, and of adenoid tissue 

 containing numerous lymphoid cells ; essentially, therefore, a 

 diffusely distributed adenoid tissue with occasional lymph-follicles 

 imbedded in its substance. The mucosa presents numerous 

 papillae, which are either simple or compound (branched) eleva- 

 tions of the mucosa, varying in length and density, according to 

 their location and extending for variable distances into the over- 

 lying epithelium. As in the papillary layer of the corium (see 

 Skin), so also here the superficial layer of the stratum proprium 

 contains very fine elastic and connective-tissue elements which con- 

 tribute to the structure of the papillae. All these papillae contain 

 capillaries and arterioles which are derived from an arterial network 

 in the mucosa. The lymphatics are similarly arranged. 



At the red margin of the lips the papillae are unusually high 

 and are covered at their summits by a very thin epithelial layer 

 (Fig. 1 80). Besides the sebaceous glands which lie at the angles 

 of the mouth, and whose ducts open at the surface, there are here 

 no other glandular structures. In the mucosa of the. mucous 

 membrane of the lips and cheeks the papillae are low and broad ; 

 here also open the ducts of compound lobular, alveolar glands, the 

 glandulce labiates and buccales whose structure is similar to that of 

 the large salivary glands (see these). The gums possess very long 

 and attenuated papillae, covered by a very thin layer of epithelium, 

 therefore bleeding at the slightest injury. That part of the gum 

 covering the tooth has no papillae. The gums contain no glands. 

 The papillae of the hard palate are arranged obliquely, with their 

 points directed toward the opening of the mouth. The papillae of 

 the soft palate are very low and may even be absent. They are 

 somewhat higher on the anterior surface of the uvula. On the 

 posterior surface of the latter occur ciliated epithelia distributed in . 

 islands between the areas of stratified squamous epithelium. In 

 the soft palate and uvula are found small mucous glands. 



Under the mucous membrane there is a layer consisting princi- 

 pally of connective tissue and elastic fibers, the submucosa (stratum 

 submucosum, tela submucosa). In the mucous membrane of the 

 mouth the transition of the tissue of the mucosa into that of the 

 submucosa is very gradual. The submucosa of the hard palate is 

 closely connected with the periosteum and contains, especially at 

 its posterior portion, numerous glands. In other regions of the 



