This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The jejunum is about 8 1/2 ft. long and the ileum about 12 1/2 ft. They are bound to the spinal column by the mesentery, which extends from the left side of the body of the second lumbar vertebra to the right sacro-iliac joint.
The point of ending of the duodenum and beginning of the jejunum is marked by a sharp bend called the duodeuojejunal flexure. The beginning of the jejunum passes downward, forward, and usually toward the left. If the transverse colon is thrown upward and the jejunum is pulled sharply to the right, a folded edge of peritoneum containing some muscular fibres is seen passing from the flexure to the parietal peritoneum. This is called the suspensory ligament or muscle of Treitz. The fossa which is behind it is the superior duodenojejunal fossa of Treitz while that below is the inferior duodenal fossa. Below the fossa runs the inferior mesenteric artery and near the left edge of the ligament runs the inferior mesenteric vein. Into the fossae, if abnormally large, the intestines may enter and produce a retroperitoneal hernia. If the constricting band, which is the ligament of Treitz, is cut, there is danger of dividing the inferior mesenteric vein (see Fig. 420).
Fig. 420. - The duodenojejunal flexure and duodenal fossa; the jejunum drawn to the right.
The walls of the jejunum are thicker, redder, and more vascular than those of the ileum and the valvulae conniventes are better developed. The ileum is thinner, narrower, paler and, particularly when diseased, the large Peyer's patches can be seen.
The intestinal coils, while not constant in position, are most apt to be as follows: The commencement of the jejunum is in the upper left portion of the abdomen. The ileum is more in the right lower quadrant of the abdomen. According to Treves, the intestine from six to eleven feet from its commencement has the longest mesentery and is apt to be found in the pelvis. The lower end of the ileum is also usually found in the pelvis, and rises over its brim to join the caecum.
There is no certainty, however, of finding a definite piece of the small intestine under any special point on the surface, because the varying distention and movements cause frequent changes of position.
In the embryo the vitello-intestinal duct passes from the umbilicus to the lower end of the small intestine. Normally this disappears, but sometimes a portion of it remains and there is found, one to three feet above the ileocaecal valve, a finger-like projection from the side of the ileum, 5 to 7.5 cm. (2 to 3 in.) long. This is called Meckel's diverticulum, and may become the site of disease the same as the rest of the ileum. From its extremity a fibrous band may run to the umbilicus. This has been in rare instances the source of strangulation, causing intestinal obstruction. One such case has been under our care (Fig. 421).
Peyer's patches (noduli lymphatici aggre-gati) are most numerous in the lower portion of the ileum. They are ulcerated in typhoid cases and are frequently the site of perforations. These patches are from 1 to 2.5 cm. (1/2 to 1 in.) wide and 2.5 to 7.5 cm. (1 to 3 in.) long. When affected in typhoid fever they can readily be seen through the intestinal walls. By holding the intestine up against the light both Peyer's patches and the valvulae conniventes can readily be seen.
The perforations in typhoid fever occur usually within three feet of the ileo-caecal valve, though occasionally they may occur, as we have seen, in the appendix, or higher up in the small intestine, or even in the large intestine.
Fig. 421. - Meckel's diverticulum. (From author's sketch).