Physiology of Digestion. 



Fig. 150. 



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 seba- 

 ceous 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. 150), 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 

 Cells of stratified squamous acini secreting an albuminous fluid and others mucin, e.g., the 



epithelium detached from human maxillary gland. 



corpuscles * ^ && 1V3Ty Numerous mucous glands (labial, buccal, palatine, lingual, molar) 

 P ' 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 transparent 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 foliatae). They are lined with turbid granular epithelium with 

 a central nucleus, and secrete saliva. (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 sub-mucosa, 

 whilst the finer twigs penetrate into the papillae, where they form either a capillary network or 

 simple loops. 



The larger lymphatics lie in the sub-mucosa, whilst the finer branches form a fine network 

 placed in the mucosa. The lymph-follicles also belong to the lymphatic system ( 197). On 

 the dorsum of the posterior part of the tongue they form an almost continuous layer. They are 

 round or oval (1-1*5 mm. in diameter), lying in the sub-mucosa, and consist of adenoid tissue 

 loaded with lymph-corpuscles. The outer part of the adenoid reticulum is compressed so as to 



