SALIVARY GLANDS AND SALIVA. 209 



The Salivary Glands and the Saliva. 



The first of a series of changes to which the food is subjected 

 in the digestive canal, takes place in the cavity of the mouth ; 

 the solid articles of food are here submitted to the action of 

 the teeth (p. 51), whereby they are divided and crushed, and 

 by being at the same time mixed with the fluids of the mouth, 

 are reduced to a soft pulp, capable of being easily swallowed. 

 The fluids with which the food is mixed in the mouth consist 

 of the secretion of the salivary glands, and the mucus secreted 

 by the lining membrane of the whole buccal cavity. 



The glands concerned in the production of saliva, are very 

 extensive, and, in man and Mammalia generally, are presented 

 in the form of four pairs of large glands, the parotid, submax- 

 illary, sublingual, and numerous smaller bodies, of similar 

 structure and with separate ducts, which are scattered thickly 

 beneath the mucous membrane of the lips, cheeks, soft palate, 

 and root of the tongue. The structure of all these glands is 

 essentially the same. Each is composed of several parts, called 

 lobes, which are joined together by areolar tissue ; and each of 

 these lobes, again, is made up of a number of smaller parts 

 called lobules, bound together as before by areolar tissue. Each 

 of these small divisions, called lobules, is a miniature represen- 

 tation of the whole gland. It contains a small branch of the 

 duct, which, subdividing, ends in small vesicular pouches, 

 called acini, a group of which may be considered the dilated 

 end of one of the smaller ducts (Fig. 67). Each of the acini 



Diagram of a racemose or saccular compound gland : TO, entire gland, showing 

 branched duct and lobular structure ; n, a lobule detached, with o, branch of duct 

 proceeding from it (after 8harpey). 



is about ^j of an inch in diameter, and is formed of a fine 

 structureless membrane, lined on the inner surface and often 

 filled by spheroidal or glandular epithelium ; while on the out- 

 side there is a plexus of capillary bloodvessels. The accom- 

 panying diagram is intended to show the typical structure of 

 such glands as the salivary (Fig. 67). 



