Page:Encyclopædia Britannica, Ninth Edition, v. 7.djvu/241

live tissue; <?, racemose gland; d, its duct; a, artery ending in a capillary plexus on the gland vesicles. X 40. continuous through the several openings with the mucous membrane lining the Eustachiam tubes, nose, mouth, larynx, and oesophagus. The epithelium covering the mucous membrane of the nasal part of the pharynx is columnar and ciliated over a considerable surface, but elsewhere the pharyngeal epithe lium is tesselated and stratified: and in the latter localities, vas- cular papillae project into the epithelial layers. Small race mose glands lie be neath the mucous membrane, which is pierced by their ducts to open on the sur face (fig. 2); they are most numerous _ , . . FIG. 2. Vertical section through the mucous mem- Ill the nasal part OI brane of the pharynx, to show the racemose the pharynx. Col- F. lunds : , 0>e epithelium; rt, subjacent connec- lections of lymphoid tissue are found in the sub-epithelial connective tissue, more especially in the nasal part of the pharynx, Avhere it forms a mass, extending across the posterior and upper wall, between the openings of the two Eustachian tubes, which Luschka has called the phai-yngeal tonsil. The arteries of the pharynx are derived from the external carotid or some of its branches. The motor, sensory, and sympathetic nerves unite to form the pharyngeal plexus situated behind the middle constrictor muscle. The Soft Palate forms an inclined plane, which pro jects, downwards and backwards into the pharynx, from the posterior border of the hard palate. It is less dependent at the sides than in the mesial plane, where it forms an elongated body, the uvula. Its anterior or oral surface is smooth, and gives origin on each side to a fold, which curves downwards to the side of the root of the tongue, to form the anterior pillars of the palate or fauces. Its posterior or pharyngeal surface, also smooth, gives origin on each side to a fold, which, springing from the base of the uvula, curves downwards and backwards to be lost in the side-walls of the pharynx; this pair of folds forms the posterior pillars of tlierjalate or fauces. The soft palate is complex in structure, and consists of muscles, mucous membrane, glands, blood and lymph vessels, and nerves. The muscles of the soft palate are arranged in two groups, those which elevate and make it tense, and those which constrict the fauces. The mucous membrane of the soft palate is continuous with that of the mouth and pharynx. The epithelium covering the anterior or oral surface is a stratified pavement epithelium. That on the posterior or pharyngeal surface is in infancy a laminated cylindrical and ciliated epithelium, with isolated areas of pavement epithelium, but in adults it is a laminated pavement epithelium. Numerous racemose mucous glands lie beneath the mucous membrane, but much more abundantly on the oral than on the pharyngeal aspect. Collections of lymphoid tissue, similar to those found in the tonsils, are also met with. The arteries are branches of the internal maxillary, facial, and ascending pharyngeal. The veins of the soft palate often assume a dilated character, and are continuous with the pharyngeal veins. Lymphatics are also distributed beneath the mucous membrane. The (Esophagus] or Gullet, is an almost cylindrical tube, about 9 or 10 inches long, which transmits the food from 223 the pharynx to the stomach. It commences in the neck opposite the body of the sixth cervical vertebra, where it is continuous with the pharynx. It passes down the lower part of the neck, traverses the cavity of the thorax, pierces the diaphragm at the eesophageal opening, enters the abdomen, and becomes continuous with the cardiac end of the stomach close to that opening. Structure. The wall of the oesophagus consists of three coats, named, from without inwards, muscular, submucous, and mucous coats. The muscular or external <:oat is divided into two layers, an external and an internal. The external layer is com posed of fibres arranged longitudinally in the wall. The internal layer consists of fibres arranged in a series of rings around the tube, which lie sometimes horizontally, at others obliquely. The muscular coat in the upper fourth of the oesophagus is red, and its fibres are transversely striped; in the second fourth numerous non-striped fibres are mingled with the striped; whilst in the lower half the coat consists exclusively of non-striped fibres. By the contraction of the fibres of the muscular coat the food is propelled down wards into the stomach. The subnmcous coat connects the muscular and mucous coats with each other. It consists of bundles of white fibrous tissue intermingled with elastic fibres, and the nerves and blood-vessels passing to the mucous coat ramify in it. The mucous or internal coat lines the interior of the tube, and is continuous above with the mucous lining of the pharynx, and below with that of the stomach. When the oesophagus is empty it is thrown into longitudinal folds. Its free surface is covered by a thick layer of stratified squamous epithelium, which terminates abruptly at the car diac orifice of the stomach in an irregular line. Projecting into the epithelium are multitudes of minuteconical papillae. Opening on the surface of the membrane are the ducts of numerous small racemose glands similar to those in the pharynx (fig. 2). Collections of lymphoid tissue, form ing solitary follicles, are also found in the mucous membrane. The deep surface of the mucous membrane consists of a layer of non-striped muscular tissue, the bundles of which run longitudinally; it forms the muscular layer of the mucous coat, or muscularis mucosce. The oesophagus is supplied with blood by the inferior thyroid artery, the cesophageal branches of the thoracic aorta, and the ascending branch of the coronary artery of the stomach. The nerves are derived from the pneumo- gastrics. which form plexuses containing nerve-cells, not only in the muscular coat, but in the muscularis mucosse. A network of lymphatic vessels also occurs in both the mucous and submucous coats. ABDOMINAL CAVITY AND PEEITONETJM. As the remaining por tions of the alimentary canal are situated in the abdominal cavity, it will be advisable, before describing their anatomy, to give an ac count of the form and boundaries of that cavity, of its division into regions, and of the general arrangement f the peritoneum, which constitutes its lining membrane. The Abdominal Cavity, Abdomen, or Belly, is the largest of the Abdom three great cavities of the body. It occupies about the lower two- thirds of the trunk, and extends from the diaphragm above to the pelvic floor below. As its walls, except in the pelvic region, aro chiefly formed of muscles and of fibrous membrane, they are much more distensible than those of the thorax, and permit considerablo modifications to occur in the size of the viscera contained within the cavity. The abdomen is elongated in form; its vertical diameter is greater than either the transverse or the antero -posterior diameter. The superior boundary is formed by the concave vault of the diaphragm, and by the seven lower pairs of ribs and costal cartilages; in this boundary occur the opening through which the oesophagus passes into the abdomen, and also the apertures for the transmission of the great blood-vessels, the nerves, and the thoracic duct. The inferior boundary is formed by the levatores ani and coccygei muscles, and the pelvic fascia; in relation to this boundary

are the termination of the rectum and anal orifice, the termination