DIGESTION. 145 



The glands embedded in the mucous membrane covering the tongue, 

 lips, cheek, palate, and pharynx are for the most part lined with epithelial 

 cells which contain a highly refracting matter similar to, if not identical with, 

 that found in the cells of the submaxillary and sublingual glands. 



Nerve-supply. Histologic investigation has demonstrated that the 

 cells and blood-vessels of the salivary glands are supplied with nerve-fibers 

 directly from ganglion cells situated in their immediate neighborhood. 

 Thus the cells and blood-vessels of the submaxillary and sublingual glands, 

 receive nerve-fibers from the submaxillary, sublingual and superior cervical 

 ganglia, while the cells and blood-vessels of the parotid gland receive nerve- 

 fibers from the otic and the superior cervical ganglia. From their ultimate 

 distribution it may be inferred that some of the ganglion cells and fibers 

 influence the production of the secretions (secretor nerves), while others 

 influence the caliber of the blood-vessels causing either constriction or dilata- 

 tion (vaso-constrictor and vaso-dilatator nerves). (Fig. 67.) The secretor 

 fibers penetrate the basement membrane enclosing the gland acinus and 

 finally terminate between and on the surface of the secretor cells. The 

 vaso-motor fibers terminate between and on the muscle cells in the walls of 

 the blood-vessels. 



The local ganglion cells, however, are in anatomic relation with nerve- 

 trunks coming directly from the medulla oblongata and the spinal cord. 

 As they enter the ganglia, their terminal branches arborize around and 

 closely invest the cells of the ganglia and come into intimate histologic and 

 physiologic connection with them. The nerve-fibers coming from the 

 central nerve system are known as pre-ganglionic fibers, while those coming 

 from the ganglia are known as post-ganglionic fibers. Through the inter- 

 mediation, therefore, of the ganglion cells, the secretor cells of the salivary 

 glands and the blood-vessels surrounding them are brought into relation 

 with the central organs of the nerve system and become susceptible of being 

 influenced by them. 



The Parotid Saliva. The parotid saliva, as it flows from the orifice of 

 Stenson's duct, is clear, limpid, free from viscidity, distinctly alkaline in 

 reaction, with a specific gravity of 1.003. Chemic analysis shows that it 

 consists of water, a small quantity of protein matter, a trace of a sulpho- 

 cyanogen compound, and inorganic salts. The secretion is increased during 

 mastication, and especially on the side engaged in mastication. Dry food 

 causes a larger flow than moist food. The situation of the orifice of the 

 parotid duct is such that as the secretion is poured into the mouth it is at 

 once incorporated with the food by the movements of the lower jaw, and 

 thus fulfils the physical function of softening and moistening it. 



The Submaxillary Saliva. The submaxillary saliva is clear, slightly 

 viscid, alkaline in reaction, and has a specific gravity of 1.002. It consists 

 of water, protein matter (mucin), and inorganic salts. 



The Sublingual Saliva. The sublingual saliva is clear, extremely 

 viscid, and strongly alkaline in reaction. It consists of water, protein 

 matter (chiefly mucin), and inorganic salts. 



The small racemose glands embedded in the mucous membrane on 

 the inner surface of the cheeks and lips, on the hard and soft palate, and on 



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