408 



APPLIED ANATOMY. 



Third portion: In front are the superior mesenteric artery and root of the 

 mesentery; behind lie the vena cava, aorta, and left psoas muscle. Above, it lies 

 in contact with the pancreas. The termination of the duodenum is usually on the 

 left of the aorta, but Dwight (Journal of Anatomy and Physiology, vol. xxxi, p. 

 576) in fifty-four cases found it twenty-six times on the right of the aorta until just 

 before its terminal flexure. It was wholly on the right side six times, in front of the 

 aorta eleven times, and had crossed the aorta eleven times. 



Peritoneal Covering. First part: The pyloric half is almost completely 

 covered by peritoneum, but the distal half only on its anterior surface. Second part: 

 No peritoneum on its inner and posterior surfaces, and only on its outer and anterior 

 where not covered by the transverse colon. Third and fourth parts: The anterior 

 and left sides are covered by peritoneum except where crossed by the root of the 

 mesentery and superior mesentric vessels. 



JEJUNUM AND ILEUM. 



The jejunum is about 8j/ ft. long and the ileum about 12 J^ 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. 



Duodenojejunal Flexure and Fossae. The point of ending of the duo- 

 denum and beginning of the jejunum is marked by a sharp bend called the ditodeno- 



Duodenojojunal flexuic 



Middle colic artery 



Suspensory ligament or 

 muscle of Treitz 



Superior duodenal fossa 

 Inferior mesenteric vein 



Inferior duodenal fossa 

 Fourth portion of duodenum 

 Inferior mesenteric artery 



FK;. 420. The duodenojejunal flexure and duodenal fossa; the jejunum drawn to the right. 



jejunal 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). 



The small intestine decreases in size and thickness from its upper to its lower 

 end. The diameter of the jejunum is about 4 cm. (i^ in.) while that of the ileum 

 is about 3 cm. (i^ in.). 



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, nar- 

 rower, 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 



