Page:Encyclopædia Britannica, Ninth Edition, v. 7.djvu/247

229 DIGESTIVE ORGANS 229 in two layers from witnout inwards. The outer layer con sists of longitudinal fasciculi, which are not as a rule dis tributed uniformly in the wall, but in the caecum and colon are collected into three longitudinal bands, which start from the cfecum, where it is joined by the appendix vermiformis, and extend along the colon to the rectum. As these bands are not so long as the colon itself, they occasion the puckerings which separate the sacculi, so that when the bands are cut through the sacculi disappear. The colon then becomes more elongated and cylindriform. In the appendix vermiformis the longitudinal layer is not collected into bands, but arranged uniformly along the wall. In the rectum, also, the longitudinal layer is spread uniformly along the wall, and forms a well-defined red-coloured layer. The inner layer of the muscular coat consists of circular fasciculi distributed around the wall of the large intestine. In the rectum this layer increases in thickness, and in proximity to the anus forms a circular muscle, the sphincter ani interims, which is a strong band, about half an inch broad, around the lower end of the rectum. In the large, as in the small intestine, the muscular coat occasions the peristaltic movements, and its increased thickness in the rectum is for the purpose of expelling the fieces. The submucous coat has similar relations and structure to the corresponding coat in the small intestine. The mucous or internal coat is not thrown into valyulse conniventes, but presents a series of well-marked permanent ridges, lying transversely or somewhat obliquely to the long axis of the gut, and corresponding internally to the constric tions, which, on the outer surface of the colon, separate the sacculi from each other. The mucous membrane of the large intestine is covered by a layer of columnar epithelium. It is devoid of villi, and consists of a glandular and a muscular layer. The secreting glands of the glandular layer have the form and structure of the Lieberkiihuian glands of the small intestine (fig. 7) ; they open on the free surface of the mucous coat, and, owing to the absence of villi, their mouths are more closely set together than is the case with the corresponding glands in the small intestine ; the tubular glands are separated by a retiform tissue with lymphoid corpuscles. Solitary glands, similar to those in the small intestine, are also present, but no Peyer s patches. The muscularis mucosse resembles generally that of the small intestine. Of the blood-vessels of the large intestine, the arteries are principally derived from branches of the superior and inferior mesenteric arteries, but the lower end of the rectum receives the h;emorrhoidal branches of the internal iliac and the pudic. The veins which correspond to these arteries for the most part join the superior and inferior mesenteric veins, and are consequently rootlets of the portal. But the veins which belong to tbe middle and inferior hsemorrhoidal arteries forma plexus about the anal orifice, which partly joins the superior hajmorrhoidal vein, and through it the portal vein, and is partly connected through the middle and inferior Iraemorrhoidal veins with the internal iliac vein, and through it with the inferior vena cava. The veins about the anus are very apt to become varicose, and to form the excrescences termed haemorrhoids or piles. The lymph vessels are arranged as in the small intestine, except that they are not prolonged into villi. Nervous plexuses with ganglion cells are fcund in both the muscular and submucous coats. They proceed from the superior and inferior mesenteric plexuses, but the rectum receives branches from the hypogastric plexus, and from the third and fourth sacral spinal nerves. The LIVER is the biggest of the abdominal viscera, and the largest gland in the body. It is the organ in which the secretion of bile takes place, and is the chief seat in the body of the formation of glycogen, a substance like dextrin, which readily undergoes conversion into sugar. It lies in the costal zone of the abdomen, fills up the greater part of the right hypochondrium, and extends, through the epigastrium, into the left hypochondrium. In its long or transverse diameter it averages about 12 inches, in its antero-posterior diameter about 6 inches, in the vertical diameter of its thickest part about 3 inches. Relatively to the size of the body the liver is bigger and heavier iu the foetus than in the adult ; soon after birth the relative weight declines, and that of the left lobe diminishes much more rapidly than the right lobe. Frerichs states that the relative weight of the healthy liver fluctuates in adults between o^-th and ^th of that of the body, and the absolute weight varies from 1 8 to 4 6 pounds avoird. During the digestion of the food the liver increases both in size and weight, partly from the greater quantity of blood flowing through it, and partly from the new material in the secreting cells ; whilst after a long fast it becomes smaller and lighter. For descriptive purposes the liver may be regarded as having two surfaces, two borders, and two extremities. The superior or diaphragmatic surface is smooth and convex, aud attached to the diaphragm by the falciform ligament. The posterior or vertebral border is comparatively thick, and attached by the coronary ligament to the diaphragm. The anterior border of the liver is unattached, thin, and attenuated, and is marked by a deep notch, opposite the anterior edge of the falciform ligament, which lodges the round ligament of the liver. Of the two extremities of the liver the rigid is thick and massive, and lies deep in the right hypochondrium, in con tact with the diaphragm ; the left is thin and attenuated, and overlaps the oesophageal opening and fundus of the stomach. The inferior or visceral surf ace of the liver is much more complex in form than the upper. The longitudinal or umbilical fissure, continuous with the notch in the anterior border of the liver, and much nearer to the left than the right extremity of the gland, divides it into a large right FIG. 8. Under surface of the liver. R, right lobe; L, left lobe ; Q, lobus qtind- ratus; S, lobus Spigelii ; C, lobus caudatus : p, pons hepatis; //.longitudinal fissure; t, transverse fissure; cf. caudate fissure; vf, fossa for vena oava; kf, fossa for right kidney; G, gall bladder in its fossa; u, obliterated umbilical vein; v, obliterated ductus venosus; IV, inferior vena cava; h, h, hepatic veins; P, portal vein; A, hepatic artery; D, bile duct; c, coronary ligament; II and rl, left and right lateral ligaments ; s, suspensory ligament ; r, round ligament. and a small left lobe. In the anterior part of the fissure the round ligament, formed by the obliteration of the umbilical vein of the fcetus, is lodged ; whilst the posterior part contains a slender fibrous cord formed by the oblitera tion of a vein of the foetus, named ductus venosus. Tha longitudinal fissure is often bridged across by a band cf