DIGESTION. 



pouches, around which a delicate network of blood-vessels 

 is arranged: they empty into the mouth by means of 

 little tubes, or 

 ducts. The flow 

 from these glands 

 is at all times suf- 

 n'cient to maintain 

 a soft and moist 

 condition of the 

 tongue and mouth; 

 but when they are 

 excited by the pres- 

 ence and taste of 

 food, they pour 



forth the Saliva FlG - 20- STRUCTURE OP A SALIVARY GLAND. 



more freely. Even the mere thought of food will at 

 times cause the saliva to flow, as when the appetite is 

 stimulated by the sight or smell of some savory article ; so 

 that the common expres- 

 sion is correct that " the 

 mouth waters" for the fa- 

 vorite articles of food. 

 Anxiety and grief prevent 

 its flow, and cause "the 

 tongue to cleave to the 

 roof of the mouth." In 

 the horse and other ani- 

 mals, that feed upon dry 

 and coarse fodder, and re- 



-i -t FIG. 21. THE HEAD OP A HORSE, showing the 



quire an abundant SUp- large salivary gknd (a), its duct (6), the 



ply of saliva, we find large 



salivary glands, as well as powerful muscles of mastication. 



16. The mingling of the saliva with the food seems a 



simple process, but it is one that plays an important part 



1 6. Importance of the process ? The first place ? The second ? The third ? 



