Salivary Glands, those glands which secrete the saliva, the principal of which are the parotid, the submaxillary, and the sublingual, disposed in pairs. The parotid, the largest gland, weighing from half an ounce to an ounce, is immediately below and in front of the ear and the zygomatic arch, reaching down as low as the angle of the lower jaw. Its outer surface, slightly lobulated, is covered by the skin and fascia, and its inner surface extends deeply into the neck by two processes, one of which dips behind the styloid process and beneath the mastoid process of the temporal bone and the sterno-mastoid muscle, and the other is situated in front of the styloid process. The external carotid artery passes through the substance of the gland. It is also traversed by the posterior auricular, transverse facial, temporal, and internal maxillary arteries, by a venous trunk formed by the union of the temporal and internal maxillary veins, and by a branch connecting this trunk with the jugular vein. The facial nerve and its branches and the great auricular nerve pass through it from before backward. The internal carotid artery and internal jugular vein lie close to its deep surface.
The duct of the parotid gland (the duct of Steno) is about 2 1/2 in. long, opening on the inner surface of the cheek by a small orifice opposite the second molar tooth of the upper jaw; it is dense, of considerable thickness, and its canal is about the size of a crow quill, composed of an external fibrous and internal mucous coat, lined with columnar epithelium. The gland is supplied with blood by branches of the external carotid artery, and with nerves from the carotid plexus of the sympathetic, the facial, the superficial temporal, the auri-culo-temporal, and great auricular nerves; and its lymphatics terminate in the superficial and deep cervical glands. The submaxillary gland is situated below the lower jaw, within and just in front of the angle, lying upon the mylo-hyoid, hyo-glossus, and stylo-glossus muscles, and is separated from the parotid by the stylo-maxillary ligament. It is irregular in form, and weighs about two drachms. It is relatively smaller in the herbivora than in the carnivora, being in the latter larger than the parotid. The facial artery lies imbedded in a groove in its posterior and upper border. Its duct (Wharton's) is about 2 in. long, much thinner than that of the parotid, and opens by a narrow orifice by the side of the fraenum of the tongue.
The gland is supplied with blood by branches of the facial and lingual arteries, and its nerves are derived from the submaxillary ganglion, from a branch of the inferior dental, and from the sympathetic. The sublingual gland is the smallest, weighing about a drachm. It is situated in the floor of the mouth at the side of the fraenum linguae, in contact with the inner surface of the lower jaw, close to its symphysis. Its excretory ducts are from 8 to 20 in number, very short, and open on the crest or projection formed by the gland itself. One or more join to form a duct known as the duct of Bartholine, which opens into Wharton's duct. The gland is supplied with blood from the sublingual and submental arteries, and with nerves from the gustatory nerve. - These three pairs of glands are of the kind called conglomerate, consisting of numerous lobes composed of smaller lobules connected together by areolar tissue, vessels, and ducts. There are other small glands lying in and beneath the mucous membrane of the mouth, such as the labial and buccal glands, the follicular glands of the tongue, and certain glandular bodies in the mucous membrane of the pharynx. (See Pharynx.) Prof. Dalton obtained pure parotid saliva from the human mouth by introducing a silver tube into the duct, and arrived at many important facts regarding its functions.
In one observation 480 grains of the secretion flowed from the tube in 20 minutes. The secretion takes place most rapidly during mastication, and on that side of the mouth where the mastication is performed, as has been shown by Colin and confirmed by Dalton. The flow is also active upon the sight or perception of the odor of food, and also from the influence of the imagination. Bernard has shown that galvanization of the small root of the fifth pair of nerves, and of the facial, immediately produces profuse secretion from the parotid. Parotid saliva is clear and limpid, and differs in composition somewhat from that of the submaxillary and sublingual glands. It contains organic matter, sulpho-cyanide of sodium, phosphate of lime, chlorides of potassium and sodium, and carbonate of soda. The function of parotid saliva is now generally regarded as chiefly to assist in mastication and deglutition. Pure submaxillary saliva was first studied as a distinct fluid by Bernard. It is more viscid than that from the parotid, but is perfectly clear, and on cooling becomes gelatinous. Its organic matter is not coagulated by heat.
Bernard regards the function of submaxillary saliva as exclusively connected with gustation or tasting, and says its secretion only takes place under the stimulus of the gustatory nerves. The secretion of the sublingual is more viscid than that of the submaxillary, but does not gelatinize on cooling. Like the secretion from the other salivary glands, it is decidedly alkaline. Its organic matter is not coagulated by heat, acids, or metallic salts. The functions and properties of the mixed saliva of all the glands of the mouth are stated in the article Digestion.