DIGESTION. 231 



INSALIVATIOST. 



The act of mastication is much assisted by the saliva which is secreted 

 by the salivary glands in largely increased amount during the process, 

 and the intimate incorporation of which with the food, as it is being 

 chewed, is termed insalivation. 



The Salivary Glands. 



The human salivary glands are the parotid, the subm axillary, and 

 the 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. 



Structure. The salivary glands are compound tubular glands. They 

 are made up of lobules. Each lobule consists of the branchings of a 



Fia. 174. Section of submaxillary gland of dog. Showing gland cells, 6, and a duct, a. in sec- 

 tion. (Kolliker.) 



subdivision of the main duct of the gland, which are generally more or 

 less convoluted towards their extremities, and sometimes, according to 

 some observers, sacculated or pouched. The convoluted or pouched 

 portions form the alveoli, or proper secreting parts of the gland. The 

 alveoli are composed of a basement membrane of flattened cells joined 

 together by processes to produce a fenestrated membrane, the spaces of 

 which are occupied by a homogeneous ground-substance. Within, upon 

 this membrane, which forms the tube, the nucleated salivary secreting 

 cells, of cubical or columnar form, are arranged parallel to one another 

 inclosing a central canal. The granular appearance frequently seen in 

 the salivary cells is due to the very dense network of fibrils which they 

 contain. "When isolated, the cells not unfrequently are found to be 

 branched. Connecting the alveoli into lobules is a considerable amount 

 of fibrous connective tissue, which contains both flattened and granular 

 protoplasmic cells, lymph corpuscles, and in some cases fat cells. The 

 lobules are connected to form larger lobules (lobes), in a similar man- 

 ner. The alveoli pass into the intralobular ducts by a narrowed portion 



