The Salivary Glands are six in number, three on each side of the mouth. Their function is to secrete a fluid called saliva, which aids in mastication. The largest of these glands, the Parotid, is situated in front and below the ear; its structure, like that of all the salivary glands, is cellular. The Submaxillary gland is circular in form, and situated midway between the angle of the lower jaw and the middle of the chin. The Sublingual is a long flattened gland, and, as its name indicates, is located below the tongue, which when elevated, discloses the saliva issuing from its porous openings.
The Pharynx is nearly four inches in length, formed of muscular and membranous cells, and situated between the base of the cranium and the esophagus, in front of the spinal column. It is narrow at the upper part, distended in the middle, contracting again at its junction with the esophagus. The pharynx communicates with the nose, mouth, larynx, and esophagus.
The Esophagus, a cylindrical organ, is a continuation of the pharynx, and extends through the diaphragm to the stomach. It has three coats: first, the muscular, consisting of an exterior layer of fibers running longitudinally, and an interior layer of transverse fibers; second, the cellular, which is interposed between the muscular and the mucous coat; third, the mucous membrane, or internal coat, which is continuous with the mucous lining of the pharynx.
The Stomach is a musculo-membranous, conoidal sac, communicating with the esophagus by means of the cardiac orifice (see Fig. 28). It is situated obliquely with reference to the body, its base lying at the left side, while the apex is directed toward the right side. The stomach is between the liver and spleen, subjacent to the diaphragm, and communicates with the intestinal canal by the pyloric orifice. It has three coats. The peritoneal, or external coat is composed of compact, cellular tissue, woven into a thin, serous membrane, and assists in keeping the stomach in place. The middle coat is formed of three layers of muscular fibers: in the first, the fibres run longitudinally; in the second, in a circular direction; and in the third, they are placed obliquely to the others. The interior, or mucous coat, lines this organ. The stomach has a soft, spongy appearance, and, when not distended, lies in folds. During life, it is ordinarily of a pinkish color. It is provided with numerous small glands, which secrete the gastric fluid necessary for the digestion of food. The lining membrane, when divested of mucus, has a wrinkled appearance. The arteries, veins, and lymphatics, of the stomach are numerous.
The Intestines are those convoluted portions of the alimentary canal into which the food is received after being partially digested, and in which the separation and absorption of the nutritive materials and the removal of the residue take place. The coats of the intestines are analogous to those of the stomach, and are, in fact, only extensions of them. For convenience of description, the intestines may be divided into the small and the large. The small intestine is from twenty to twenty-five feet in length, and consists of the Duodenum, Jejunum, and Ileum. The Duodenum, so called because its length is equal to the breadth of twelve fingers, is the first division of the small intestine. If the mucous membrane of the duodenum be examined, it will be found thrown into numerous folds, which are called valvulæ conniventes, the chief function of which appears to be to retard the course of the alimentary matter, and afford a larger surface for the accommodation of the absorbent vessels. Numerous villi, minute thread-like projections, will be found scattered over the surface of these folds, set side by side, like the pile of velvet. Each villus contains a net-work of blood-vessels, and a lacteal tube, into which the ducts from the liver and pancreas open, and pour their secretions to assist in the conversion of the chyme into chyle. The Jejunum, so named because it is usually found empty after death, is a continuation of the duodenum, and is that portion of the alimentary canal in which the absorption of nutritive matter is chiefly effected. The Ileum, which signifies something rolled up, is the longest division of the small intestine. Although somewhat thinner in texture than the jejunum, yet the difference is scarcely perceptible. The large intestine is about five feet in length, and is divided into the Cæcum, Colon, and Rectum. The Cæcum is about three inches in length. Between the large and the small intestine is a valve, which prevents the return of excrementitious matter that has passed into the large intestine. There is attached to the cæcum an appendage about the size of a goose-quill, and three inches in length, termed the appendix vermiformis. The Colon is that part of the large intestine which extends from the cæcum to the rectum, and which is divided into three parts, distinguished as the ascending, the transverse, and the descending.
The Rectum is the terminus of the large intestine. The intestines are abundantly supplied with blood-vessels. The arteries of the small intestine are from fifteen to twenty in number. The large intestine is furnished with three arteries, called the colic arteries. The ileo-colic artery sends branches to the lower part of the ileum, the head of the colon, and the appendix vermiformis. The right colic artery forms arches, from which branches are distributed to the ascending colon. The colica media separates into two branches, one of which is sent to the right portion of the transverse colon, the other to the left. In its course, the superior hemorrhoidal artery divides into two branches, which enter the intestine from behind, and embrace it on all sides, almost to the anus.