72 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



are, throughout the buccal mucous membrane, a number of 

 smaller glands of similar structure contributing to the formation 

 of saliva. The parotid gland is situated just beneath and in 

 front of the lobe of the ear; the submaxillary beneath the 

 mandible about the center of the base of the submaxillary tri- 

 angle, and the sublingual beneath the mucous membrane of the 

 mouth, just lateral to the lingual frenum. 



FIG. 33. Cells of the alveoli of a serous or watery salivary gland. (Brubaker 



after Yeo.) 



A, after rest; B, after a short period of activity; C, after a prolonged period of 

 activity. 



The duct from the parotid, Stenson's duct, runs beneath the 

 mucous membrane of the cheek to a point opposite the second 

 upper molar tooth, where is its opening into the mouth. The 

 duct from the submaxillary, Wharton's duct, discharges the 

 secretion from that gland into the mouth by the side of the fre- 

 num of the tongue. The secretion from the sublingual reaches 

 the mouth by a number of small ducts (Rivinus) which open 

 also by the side of the frenum, and sometimes as well by a larger 

 duct, Bartholin's, which runs parallel with Wharton's and 

 empties near it. 



Histology. In structure the salivary glands have been shown 

 to be of the compound tubular variety, the secreting part being 

 tubular. The parotid is a serous gland, the other two are usually 

 said to be mucous, though they contain both serous and mucous 

 cells. The ducts subdivide into smaller ducts and tubes, until a 

 distinct tubule is distributed to every acinus and becomes the 



