Physiology of Digestion. 



141. The Mouth and its Glands. 



THE mUCOUS membrane of the cavity of the mouth, which becomes continuous 

 with the skin at the red margin of the lips, has a number of sebaceous glands 

 in the region of the red part of the lip. The buccal mucous membrane consists of 

 bundles of fine fibrous tissue mixed with elastic fibres, which traverse it in every 

 direction. Papillae simple or compound occur near the free surfaces. The 

 SUb-muCOUS tissue, which is directly continuous with the fibrous tissue of the 

 mucous membrane itself, is thickest where the mucous membrane is thickest, and 

 densest where it is firmly fixed to the periosteum of the bone and to the gum ; it 

 is thinnest where the mucous membrane is most movable, and where there are 

 most folds. The cavity of the mouth is lined by stratified squamous epithelium 

 (Fig. 115, 8), which is thickest, as a rule, where the longest papillae occur. 



All the glands of the mouth, including the salivary glands, may be 

 divided into different classes according to the nature of their secretions. 



1. The serous or albuminous glands [true salivary], whose secretion 

 contains a certain amount of albumin, e.g., the human parotid. 



2. The mucous glands, whose secretion in addition to some albumin, 

 contains the characteristic constituent mucin. 



3. The mixed [or muco-salivary\ glands, some of the acini secreting 

 albumin and others mucin e.g., the human maxillary gland (Heiden- 

 hain). The structure of these glands is referred to under the salivary 

 glands. 



Numerous mUCOUS glands (labial, buccal, palatine, lingual, molar) have the 

 appearance of small macroscopic bodies lying in the sub-mucosa. They are 

 branched tubular glands, and the contents of their secretory cells consist partly 

 of mucin, which is expelled from them during secretion. The excretory ducts of 

 these glands, which are lined by cylindrical epithelium, are constricted where 

 they enter the mouth. Not unfrequently one duct receives the secretion of a 

 neighbouring gland. 



The glands of the tongue form two groups, which differ morphologically and 

 physiologically. (1.) The mUCOUS glands (Weber's glands), occurring chiefly 

 near the root of the tongue, are branched tubular glands lined with clear trans- 

 parent secretory cells whose nuclei are placed near the attached end of the cells. 

 The acini have a distinct membrana propria. (2.) The serOUS glands (Ebner's) 

 are acinous glands occurring in the region of the circumvallate papillae (and in 

 animals near the papillae foliatse). They are lined with turbid granular epithelium 

 with a central nucleus, and they secrete saliva (Henle). (3.) The glands of Blandin 

 and Nuhn are placed near the tip of the tongue, and consist of mucous and serous 

 acini, so that they are mixed glands (Podwisotzky). 



The blood-vessels are moderately abundant, and the larger trunks lie in the 



