Page:Encyclopædia Britannica, Ninth Edition, v. 7.djvu/243

DIGESTIVE ORGANS 225 occasion a longitudinal shortening and transverse constric tion of the stomach. By the action of the muscular coat the food is churned about in the stomach, so as to become thoroughly intermingled with the gastric juice. The con traction of the sphincter pylori closes the pyloric orifice, and prevents the passage of the food into the duodenum, before it is converted into chyme. The submucous coat consists of the areolar variety of connective tissue, and lies immediately subjacent to the oblique layer of the muscular coat. The mucous or internal coat lines the cavity of the stomach, and is continuous with the mucous membrane of the oesophagus and duodenum. It is a soft, pulpy membrane, of a pink colour, which becomes redder during digestion, owing to turgescence of the blood-vessels. At the pyloric end it is often stained yellow or green with bile, and in old people it has a brown colour, from formation of pigment. In the empty stomach it is thrown into folds or rugae, which have usually a longitudinal direction, but when distended the rugae are obliterated, and the surface of the mucous membrane is smooth. This membrane is commonly said to be thicker at the pyloric end than in the fuudus ; but Brinton, who had opportunities of examining the stomach of healthy young adults immediately after death, found the cardiac mucous membrane to be more than twice as thick as the pyloric. He ascribes the thinning of the cardiac mucous membrane to the effects of post mortem digestion, owing to the gravitation of the gastric juice, in the recumbent position of the dead body, into the fundus of the stomach. If the free surface of the gastric mucous membrane be examined with a pocket lens it will be seen to be pitted with shallow depressions or alveoli, polygonal in form, and varying from y^jth to ^-^th inch in diameter. In the sides and bottom of each of these pits numerous rounded orifices may be seen, which are the mouths of the gastric secreting glands. If vertical sections be now made through ths mucous membrane, these glands will be seen to be tubular in form. In the human stomach the tubular glands are, for the most part, simple, almost straight cylinders, and possess an average length of ^Vth inch, and a breadth of about -ji-jjth inch. They are somewhat dilated at their orifices, and at their closed ends give rise to coecal pouches. For about the upper fourth or fifth of their length the tubes are lined by a single layer of columnar epithelium, continuous with the columnar epithelium covering the free surface of the gastric mucous membrane. In the rest of the gland-tube Brinton found two kinds of cells. The one,"the so-called peptic cells, about y^V^jth mcn i 11 diameter, and of an ovoid or somewhat polygonal form, lay next to the wall of the gland. The other kind, somewhat cubical in form, lined the very narrow central canal of the gland, and formed an axial layer, which was continuous above with the columnar epithelium lining the upper end of the tube. It is in the dog and cat, however, that the structure of the gastric mucous membrane has especially been studied, and two kinds of glands have been described. The one, situated especially in the region of the pylorus, consists for the most part of simple tubes, which may, however, branch at their deeper end ; they have been called the mucus glands. They are lined by a columnar epithelium, the cells of which at the deeper end of the gland are more cubical in form, and have a clouded granular appearance. The other kind of gland is situated in the remaining part of the gastric mucous membrane, and consists of tubes which divide usually into four branches ; they have been named the peptic glands. The cellular lining of these peptic glands closely corresponds with the dimorphous arrangement in the human stomach already referred to. Heidenhain of a cat, to show the tubular peptic glands, c, columnar epithelium near the gland mouth; p, peptic cells; m, interglandular muscular band; v, vessels surrounding tubular gland; mm, muscularis mu- COS32 ; SOT submucous coat. states that in a fasting dog the glands are shrunken, and the axial cells are transparent, whilst during digestion the peptic glands are swollen out and the cells are clouded and granular. The gastric glands are separated from each other by slender pro longations of the muscularis mu- cosse. and by the vascular inter- glandular connective tissue, which is soft and delicate, and contains a small proportion of lymphoid corpuscles diffused in it. In some localities the lymphoid tissue may be collected into solitary follicles, forming the lenticular glands of the stomach. Beneath the glands is a well-defined muscularis mu- cosce, arranged in two layers, which gives off bundles that pass between the gastric glands. The gastric mucous membrane is highly vascular; small arteries enter it from the submucous coat, and terminate in a capil lary plexus, situated in the inter- glandular connective tissue sur rounding the gastric glands ; a vascular capillary ring surrounds the orifice of each gland. The pyloric valve is the name given to the circular fold, situated at the junction of the stomach and duodenum, which surrounds the pyloric orifice. This fold is covered on its free surface by mucous membrane, which incloses the submucous coat and the circular layer of the muscular coat, but not the longitudinal layer, or the serous coat. That portion of the mucous membrane which covers the gastric surface of the valve possesses the structure of the mucous membrane of the stomach ; whilst that which covers the duodenal surface is studded with villi, and possesses the structure of the intestinal mucous membrane. The arteries of the stomach form arches along the greater and lesser curvatures, and anastomose in the anterior and posterior walls of the stomach. The veins of the stomach are rootlets of the portal vein. The lymphatics are numer ous, and form a superficial and a deep set. The nerves of the stomach are derived from the epigastric plexus of the sympathetic and from the pneumogastric nerves. The Intestinal Canal, Intestine, Gut, or Boivel, is situated intestinal in the abdominal cavity, and extends from the pyloric canal, opening, or gate, of the stomach to the orifice of the anus. In it the chyme becomes mingled with the bile, the pan creatic fluid, and the secretions of the intestinal glands, and is converted into chyle. In it also the absorption of the chyle takes place, and the insoluble part of the food is passed onwards to be excreted in the form of fseces. The intestine is the longest division of the alimentary canal, and measures on an average about 25 feet. It is primarily divided into two parts, called small intestine and large intestine ; the length of the small is about 20 feet, that of the^ large about 5 feet. The Small Intestine is the upper of the two divisions of Small the canal, and consists of a convoluted, almost cylindrical intestine. tube, which reaches from the pylorus to the caecum, or commencement of the large intestine. It is subdivided into three portions, named duodenum, jejunum, and ileum. The Duodenum is the commencement of the small intestine, and has received its name from its length being regarded as about equal to the breadth of twelve fingers. It forms the shortest and widest of the three sub-divisions of the small bowel ; it curves, in the form of a horse-shoe, from the pylorus to opposite the left side of the body of