MOUTH CAVITY. 155 



layers. When there are many layers the superficial cells are 

 flattened, as in stratified epithelium. Under the epithelium 

 there is a connective-tissue layer, the tunica propria or stratum 

 proprium. Under this is a firm connective-tissue coat, the tela 

 submucosa or stratum submucosum. This combines the mucosa 

 with the underlying parts. 



A. MOUTH CAVITY. 

 1. Mucous Membrane of the Mouth Cavity. 



The epithelium of the mouth cavity is a stratified pave- 

 ment-epithelium. It is not, as a rule, corneous, and the 

 stratum granulosum and stratum lucidum are usually absent. 



The tunica propria consists of interlacing bundles of con- 

 nective-tissue fibres, among which are many elastic fibres. On 

 the surface the tunica propria forms so-called papillce, of which 

 the highest are found in the red border of the lips and in the 

 gums (Plate VIII.). At the border of the lips we find seba- 

 ceous glands, but these are absent elsewhere in the mucous 

 membrane. 



Everywhere in the tunica propria we find the ducts of 

 mucous glands (glandulse buccales, palatine, et labiales), whose 

 bodies lie in the submucosa. These are branched tubular 

 glands whose ducts are lined usually with stratified epithelium. 

 The details of their structure will be discussed with the larger 

 glands of the mouth cavity. 



The tela submucosa is a firm connective- tissue layer pos- 

 sessing only very few elastic fibres. On the gums the mucosa 

 is attached firmly to the underlying structures. Elsewhere it 

 is more loosely connected with the submucosa. The blood- 

 vessels form two plexuses more or less parallel to the sur- 

 face. The deeper, which consists of larger vessels and wider 

 meshes, lies in the submucosa ; the upper is made up of a fine 

 meshwork of small vessels which are derived from the deeper 

 layer and is situated in the tunica propria. From these net- 

 works fine branches proceed to the papillae, where a capillary 

 plexus is formed. The lymph-vessels follow a course very 



