SALIVA. 197 



is about two inches (5 centimetres) in length and passes from the gland, be- 

 neath the tongue, to open by a small papilla by the side of the frenum. 



The pure submaxillary saliva presents many important points of difference 

 from the secretion of the parotid. It may be obtained by exposing the duct 

 and introducing a fine silver tube, when, on the introduction of any sapid 

 substance into the mouth, the secretion will flow in large, pearly drops. This 

 variety of saliva is much more viscid than the parotid secretion. It is per- 

 fectly clear, and on cooling, it frequently becomes of a gelatinous consist- 

 ence. Its organic matter is not coagulable by heat. It contains a sulpho- 

 cyanide, but in very small quantity. 



The submaxillary gland pours out its secretion in greatest abundance when 

 sapid substances are introduced into the mouth ; but unlike the parotid saliva, 

 the secretion does not alternate on the two sides with alternation in mas- 

 tication. Although sapid articles excite an abundant secretion from the 

 submaxillary glands, they also increase the secretions from the parotids and 

 sublinguals ; and on the other hand, movements of mastication increase 

 somewhat the flow from the submaxillaries, and these glands secrete a certain 

 quantity of fluid during the intervals of digestion. The viscid consistence 

 of the submaxillary saliva renders it less capable than the parotid secretion 

 of penetrating the alimentary mass during mastication. 



Sublingual Saliva. The sublinguals, the smallest of the salivary glands, 

 are situated beneath the tongue, on either side of the frenum. In minute 

 structure they resemble the parotid and the submaxillary glands. Each gland 

 has a number of excretory ducts, eight to twenty, which open into the mouth 

 by the side of the frenum ; and one of the ducts, larger than the others, 

 joins the duct of the submaxillary gland near its opening in the mouth. 



The secretion of the sublingual glands is more viscid, even, than the sub- 

 maxillary saliva, but it differs in the fact that it does not gelantinize on cooling. 

 It is so glutinous that it adheres strongly to any vessel and flows with diffi- 

 culty from a tube introduced into the duct. Like the secretion from the 

 other salivary glands, its reaction is distinctly alkaline. Its organic matter is 

 not coagulable by heat, acids or the metallic salts. 



It has been shown that the sublingual glands may be excited to secretion 

 by impressions made by sapid substances upon the nerves of taste, although 

 the flow is always less than from the submaxillary glands. The great viscid- 

 ity of the sublingual saliva renders it less easily mixed with the alimentary 

 bolus than the secretions from the parotid or the submaxillary glands. 



Fluids from the Smaller Glands of the Mouth, Tongue and Pharynx. 

 Beneath the mucous membrane of the inner surface of the lips, are small, 

 rounded, glandular bodies, opening into the buccal cavity, called the labial 

 glands ; and in the submucous tissue of the cheeks, are similar bodies, called 

 the buccal glands. The latter are somewhat smaller than the labial glands. 

 Two or three of the buccal glands are of considerable size and have ducts 

 opening opposite the last molar tooth. These are sometimes distinguished as 

 the molar glands. There are also a few small glands in the mucous mem- 

 brane of the posterior half of the hard palate ; but the glands on the under 



