THE DIGESTIVE SYSTEM. 1 67 



Salivary Ducts in Our Mouths. If the inside of one's cheek be 

 examined by the use of a hand mirror, the opening of the duct from the 

 parotid gland may be seen opposite the second molar of the upper jaw. 

 It usually looks like a pink and white spot, resembling a wound of a 

 bee sting. Sometimes saliva may be seen issuing from it. 



Action of the Salivary Glands. The salivary glands 

 pour into the mouth a liquid which they manufacture from 

 materials taken from the blood. In structure the gland 

 may be compared to a bunch of grapes^ the grapes repre- 

 senting the little cavities, with a wall of cells that make 



Mucous Membrane 



Duct of Gland 



Secreting Cells 



Fig. 57. Diagram of a Salivary Gland. (.After Landois and Stirling.) 



the saliva. From these cavities the liquid passes into the 

 individual duct, represented by the stem of a single grape ; 

 many of these unite to form the main stem, which corre- 

 sponds to the main duct. A rich network of capillaries 

 surrounds the gland ; when the gland is at work it receives 

 more blood ; the liquid part of the blood (plasma) soaks 

 out through the capillary walls and surrounds the gland ; 

 it is now called lymph ; from the lymph the gland directly 

 obtains its material. 



