174 



DIGESTION 



fluid contains several inorganic salts, notably potassium sulphocyanate. 

 The quantity of saliva secreted in twenty-four hours in health appears to 



FIG. 80 



FIG. 81 



Section of salivary gland: a, alveolus; 6, connective tissue which will be seen to penetrate 

 the gland dividing it into lobes; c, points to the center of a lobe; d, septum between lobes; 

 e, gland duct lined by columnar epithelium. (Bates.) 



be rather more than a liter, the variation being large. Probably the three 

 large glands, parotid, submaxillary, and sublingual, secrete the saliva 



into the mouth only during masti- 

 cation. The other glands (the 

 buccal, labial, lingual, and molar) 

 are relied upon to keep the mouth, 

 pharynx, and tongue moist, a con- 

 dition necessary to mucous mem- 

 branes. 



The teeth are the organs by 

 which the food that is in need of 

 it is cut and ground into fine 

 pieces, or a paste, preparatory 

 to being swallowed and digested 

 farther on in the alimentary 

 canal. They are developed in 

 two sets. On rare occasions a 

 third set may be started. 

 The temporary set consists of 



Molars 



Canine 



The temporary teeth. The numbers denote 

 the respective times of their eruption in months. 

 (Hall.) 



twenty teeth, half of them in 

 each jaw. Beginning in the mid- 

 dle line on either side of each jaw 

 are two incisors, one canine, and 

 two molars. These break through the gums nearly in pairs at in- 

 tervals between the end of the first half-year after birth and the begin- 



