The above relations of this first portion of the duodenum to the peritoneum confer upon it a mobility which approaches that of the stomach ; while its close proximity to the gall-bladder explains that discoloration by bile which is generally seen in the dead intestine,— as well as the adhesion and ulceration of its parietes, hich so frequently occur in the course of disease of the liver or gall-bladder.
The second, the descending or vertical por tion, which is rather less than three inches long, passes downwards, and slightly inwards, to the right side of the third lumbar vertebra. Above it is the right lobe of the liver. In front it is crossed by the right extremity of the transverse colon. Behind it is the inner border of the right kidney-, together with a variable extent of its anterior surface, and its emulgent vein. On its right side is the ter mination of the ascending colon. On its left it is intimately connected: with the head of the pancreas. Every one of these anatomical relations has more or less pathological im portance.
The partial covering of peritoneum received by this portion of the duodenum may be traced, from the front of the great omentum, to the anterior surface of the intestine ; and around its external or right side, to the wall of the abdomen. Here it is fixed to the right kidney, by an attachment that is sometimes termed the ligamentum duodeni renale. The posterior and left surfaces of the intestine, which are devoid of this serous membrane, are connected with the neighbouring organs by a loose areolar tissue, that concedes to the tube a considerable degree of distention and movement.
The third or inferior transverse portion is about five inches in length. In its course across the spine it lies upon the structures already named. Above it is the lower border of the pancreas. In front of it is the pos terior or attached border of the transverse meso-colon,— the superior lamina of which covers it above, the inferior below, so as to leave an uncovered space along the line of their bifurcation. Anteriorly to this double proces of peritoneum, is the large and moveable transverse colon which it serves to attach. And close to the commencement of the mesentery the end of the duodenum is crossed by the superior mesenteric artery and nerves.
Owing to this very partial covering of serous membrane, the inferior transverse portion of the duodenum is even less mobile and dilatable than either of the preceding. And, from the position of the pancreas above the intestine, distention of the latter chiefly affects its inferior surface, which may thus be rendered so convex and bulging as to cover the aorta to within a very short dis tance of its bifurcation.
Hence the duodenum becomes most fixed in the second and third divisions of its course. Its fixation and curvature may together assist in delaying the passage of its contents, and in facilitating that admixture of the biliary and pancreatic secretions to which its attachment perhaps chiefly refers. Its use as a rneans of fixing the stomach has already been suffi ciently alluded to. Its comparative immunity from hernia is explained by its site.
The jejunum and ileum.— Below the duo denum, the small intestine is loosely attached to the posterior wall of the belly by means of a double lamina of peritoneum which is called the mesentery (pkos middle, &repo', intestine.) Behind, this fold is fixed to the cellular tissue that covers the aorta and vena cava, by a line of attachment which is not quite vertical, but descends from the end of the duodenum to the commencement of the cmcum, passing very obliquely across the spine from the left to the right side of the lumbar vertebr. In front, its tvi-co split to enclose the bowel, around which they become continuous with each other. Its antero-posterior depth between these spinal and intestinal borders is about three or four inches ; but tapers away suddenly at its com mencement and termination. We may, per haps, gain a better idea of the peculiar shape of this process of peritoneum by iniagining it as a very. obtuse triangle of some flexible material. Such a triangle we may suppose fixed to the spine by a truncated apex of three inches in length. While its broad base, which is about twenty fcet long, is attached to the intestine, where it is plaited so as to occupy the lea.st possible space.