Page:Encyclopædia Britannica, Ninth Edition, v. 7.djvu/240

222 DIGESTIVE ORGANS called frcenum linguce, is prolonged to the middle line of the under surface of the tongue. In its structure the mucous lining of the mouth consists of a stratified pavement epithelium, and a sub-epithelial fibro- vascular corium, possessing numerous vascular papillae. The mucous membrane of the gum is characterized by its density and toughness, due to the numerous strongly developed bundles of connective tissue in the corium, many of which are continued into the fibrous tissue of the periosteum, which covers the alveolar surface of the jaw. The free surface of the corium of the gum possesses numer ous broad papillae, and is covered by a stratified pavement epithelium similar to that in the lips and cheeks. The mucous membrane of the hard palate is also tense and tough, though not so much so as the gum ; and the fibrous fasciculi of its corium blend with the connective tissue of the subjacent periosteum. The mucous lining of the mouth is a sensitive membrane, and receives its nervous supply from the fifth cranial nerve. The mucous membrane of the mouth is specially modified on the dorsum of the tongue, in the interval between the circurn vail ate papillae and the epiglottis, and in the sub stance of the tonsils, by the development of collections of lymphoid tissue in the sub-epithelial connective tissue, isils. The Tonsils are two almond-shaped bodies, situated, one on each side of the posterior orifice of the mouth, in the fossa between the anterior and posterior pillars of the soft palate. Their normal size is not bigger than a hazel nut, but they are very apt to enlarge, grow inwards across the posterior aperture of the mouth, and diminish the size of that opening. The free surface is marked by several rounded holes, leading into e shallow pits or crypts, which I may be either simple or branched, in the substance of the tonsil. The pits are lined by the epithelial cover ing of the mucous mem brane, into which minute papillae project. In the sub- epithelial connective tissue Of the Walls Of the Crvpts Fl - I. Vertical section through one of , ,,. , PI the tonsils, to show a pit vertically IlUmerOUS follicles OI lym- divided, e, its epithelial lining; /,/, limrl ti ssiip nrp Qitintprl inrl lymph follicles; /, /, I, lymph cells dif- ptioict tissue are situated, ana f j use d hl the connective tissue . a , sma n lymph Cells are infiltrated in artery ending in capillary blood-vessels. i ,i Slightly magnified. great numbers m the con nective tissue between the follicles. Interspersed amidst the crypts are small racemose mucous glands. The tonsils are very vascular, and capillary blood-vessels are distributed in connection with the papillae, the lymphoid tissue, and the racemose glands The tonsillar veins form a plexus in relation to the attached surface of the tonsil. wtds of Mucous and Salivary Glands of the Mouth. The ducts oi e rauntli. numerous glands, engaged in secreting mucus and saliva, open on the free surface of the mucous membrane of the mouth. Their secretion not only keeps the mouth moist, and aids therefore in articulation, but by mingling with the food assists in mastication, deglutition, and the digestive process. Each gland is characterized by being divided into small lobules, and by possessing a duct or ducts, which branch off in an arborescent manner in the substance of the gland, and finally end in the minute lobules. They al belong to the compound racemose group of glands. The mucous glands of the mouth are situated beneath its mucous lining in the following localities : (a) labial glands in the upper and lower lips, but absent at the angles of the mouth ; (b) buccal glands, scattered on the inner surface o: the cheek from the lips to the opening of the parotid duct (c 1 ) palatine glands, on the oral surface of the hard palate in the uvula, on both surfaces of the soft palate, and iu th onsils ; (d} molar glands, close to the last lower molar tooth each side ; (e) lingual glands, extending backwards from he tip of the tongue along its margin, and also on its dorsum between the circumvallate papillae and epiglottis. The ducts of these mucous glands consist of a delicate nembrane lined by a single layer of columnar epithelial ells. The terminal branches of the ducts which enter ,he lobules end in a series of saccular dilatations, the acini, alveoli, or gland-vesicles, which contain rounded or polygonal secreting cells. A collection of such vesicles onns a lobule. The lobules are bound together by inter mediate connective tissue, in which the blood-vessels divide into a capillary network, that ramifies on the outer surface of the delicate membrane forming the wall of the gland- vesicles. The salivary glands of the mouth are the parotid, sub- naxillary, and sublingual glands. The parotid gland is the largest salivary gland, and occupies the parotid hollow between the lower jaw and the external ear. Its anterior border overlaps the masseter muscle, and the excretory duct emerges out of this border. A prolongation of gland sub stance, the soda parotidis, frequently accompanies the duct for a short distance. The excretory duct of the gland, called Stenson s duct, passes forwards superficial to the masseter muscle, then pierces the cheek, and opens on its inner surface opposite the second upper molar tooth. The duct is between 2 and 3 inches long, and about the thick ness of a crow-quill. The submaxillary gland is situated immediately below the lower jaw. The excretory duct of the gland, called Wharton s duct, runs forwards and opens on the floor of the mouth by the side of the framum linguae. The sublingual is the smallest of the salivary glands, and lies under the mucous membrane of the floor of the mouth, close to the fraenum linguae. It possesses from ten to twenty small excretory ducts, the ducts of Rivinus, some of which join Wharton s duct, though the greater number open directly on the floor of the mouth near the fraenum linguae. Structure. The ducts of the salivary glands branch and terminate in the lobules, each terminal duct ending in a series of saccular dilatations, the acini, alveoli, or gland- vesicles, the wall of which, formed apparently of a membruna propria, is continuous with the simple membranous wall of the terminal duct. The terminal ducts are lined by a layer of squamous epithelium, and the gland-vesicles contain the secreting cells. The blood-vessels are distributed in the interlobular con nective tissue, and form a capillary network on the wall of the gland-ducts, and on the wall of the gland vesicles. The Pharynx is an irregularly dilated canal, which forms rharyn a common passage, connecting the mouth with the oesophagus, and the nose with the larynx, so as to be sub servient to the processes both of deglutition and respiration. Its position and connections have been described under the heading ANATOMY. The wall of the pharynx consists of three coats- an external muscular and an internal mucous coat, and an intermediate fibrous membrane, which blends with the sub- mucous coat. The muscular coat consists of three pairs of circularly arranged muscles, the constrictors of the pharynx ; and of two pairs of longitudinally-arranged muscles, the etylo-pharyngei and plato-pharyngei, with occasionally a third pair, the salpingo-pharyngei. The constrictor muscles extend from the lateral wall to the middle line of the posterior wall of the pharynx, and are named from, below upwards the inferior, middle, and superior con strictors ; they lie on three different planes, so that the inferior constrictor overlaps the middle, and the middle the superior.

The mucous coat of the pharynx lines the canal, and is