THE SALIVARY GLANDS. 



147 



serving for the lubrication of the oral mucous membrane. Such oral glands 

 include the labial, within the lips, the buccal and the molar, within the 

 cheeks. The labial glands are very numerous and constitute an almost 

 unbroken zone, something over a centimeter in width, that surrounds the 

 oral cleft just inside the margin of the red lip-area. They are alveo-tubular 

 in type, lie within the submucous layer, between the mucous membrane and 

 the muscle, and belong to the mixed mucous glands. The gland-cells, 

 although chiefly mucous in character, include limited peripheral groups of 

 serous cells arranged as demilunes beneath the basement membrane. The 

 buccal glands, smaller and more scattered, occupy the submucosa beneath 

 the buccinator muscle. They correspond in structure with the labial glands. 

 The same is true of the molar glands, several small groups on the outer 

 surface of the buccinator muscle, whose ducts pierce the cheek. 



THE SALIVARY GLANDS. 



The salivary glands include the parotid, the submaxillary and the sub- 

 lingual, all organs of some size, and elaborate secretions poured into the 

 oral cavity to assist in preparing the food for deglutition and further chemi- 



Artery . 



Intralobular i 

 duct >^ 



Duct 



Interlobular duct 



Interlobular 

 septum 



r- 



Duct 





FIG. 187. Section of small lobule of parotid gland. X 70- 



cal change. For the latter purpose, the parotid gland is of most importance 

 and in all animals maintains its character as a true (serous) salivary gland. 

 The others, the submaxillary and sublingual, are variably mixed glands, the 

 former sometimes and the latter never approaching the pure serous type. 



