DIGESTION 



173 



long and enters that cavity behind the second upper molar tooth* 

 The saliva secreted by this gland is largely of a serous variety, that 

 is, it is thin, albuminous, and highly lubricating. The submaxillary 



FIG. 78 



FIG. 79 



The stomachs of four sorts of birds: A, pelican; B, tanager; C, hawk; D, ostrich; oe, esoph- 

 agus; dm, chemical stomach; r, constrictor muscle; m, under part of stomach (reservoir); pm, 

 antrum pylori. (Haller.) 



gland, weighing about 8 gm., sends its product into the mouth by 

 Wharton's duct, which ends on both sides of the frenum linguae. The 

 sublingual gland opens by numerous small ducts (those of Rivini, from 

 ten to twenty in number), directly 

 into the mouth in various places. 

 Besides these three major glands 

 there are numerous others situated 

 about the mouth-cavity. The pro- 

 duct of these glands is largely of a 

 mucous sort, whereas the submax- 

 illary gland secretes both kinds of 

 saliva in nearly equal proportions. 



Mixed saliva as it pervades the 

 walls of the mouth is an opalescent, 

 somewhat glairy liquid, tasteless, 

 and with a specific gravity of about 

 1005. Its chemical reaction is nor- 

 mally alkaline; but when not, the 

 acidity is due to fermentation of bits of food in the mouth. In addition 

 to the organic constituents of saliva (mucin, alkali-albumin, a globulin, 

 serum-albumin, and ptyalin, which is the proper enzyme of saliva), this 



The nerve-endings in the salivary glands: 

 I, I, section in a column of cells; H, demi- 

 lune-cell; n, n, nerve-fibers. (Retzius.) 



