288 SPLANCHNOLOGY. 



"because they are parallel to the rows of molar alveoli, are two 

 in number, superior and inferior ; they are situated in the cheek, 

 along the upper and lower borders of the buccinator. They dis- 

 charge by numerous orifices in the buccal membrane. The Labial 

 glands are placed under the mucous membrane of the lips, 

 especially of the upper one. The Lingual glands are found at the 

 base of the tongue, and partly along its sides. The Staphyline 

 are situated in the soft palate, and between its anterior and 

 posterior pillars, discharging into the mouth or isthmus faucium. 



Saliva, the fluid secreted by these glands, is clear, viscid, 

 colourless, and slightly saline in taste, with a specific gravity of 

 1-005. Alkaline in reaction, it consists of water with about 

 ■ one-half per cent, of solids, including fat, albumen, and a special 

 nitrogenous principle, ptyalin, or " animal diastase," which helps 

 to convert starchy material into grape sugar. Saliva also con- 

 tains alkaline and earthy salts, with a trace of sulphocyanide of 

 potassium. The secretion of the different glands varies ; that of 

 the parotid is most watery, while that of the submaxillary and 

 sublingual is viscid. The parotid secretes most abundantly during 

 mastication, and always in direct ratio to the dryness of the food ; 

 the others secrete equally, whether the aliment be dry or moist, 

 but appear to be influenced by its taste. The sight or thought 

 of food will frequently induce a secretion from the submaxillary 

 and sublingual glands. 



The food thus becomes saturated in the mouth with two fluids, 

 -mucus and saliva, both assisting in mastication and deglutition, the 

 Jatter in addition acting upon the starchy constituents of the food. 



TEETH. 



Teeth are objects implanted in and protruding from the maxil- 

 lary alveoli. They are characterised by the hardness and density 

 of their specific tissues. Like bone, these tissues consist of earthy 

 salts, with a basis of organic animal matter. They are harder 

 than bone, which contains about 67, while teeth contain 76 i, 

 23er cent, of earthy salts. One material physical difference 

 between a bone and a tooth is that the free portion of the latter 

 bears exposure and friction with impunity, while the former can 



