The mesentery extends from the left side of the body of the second lumbar vertebra to the right sacro-iliac joint. It is from 15 to 20 cm. (6 to 8 in.) long at its root and spreads out like a fan, to be attached to the small intestine. It is comparatively thick, especially toward its root, and contains the superior mesenteric artery and veins, nerves, and lymphatics. The mesenteric lymphatic nodes are numerous, from 130 to 150 (Quain) in number. They are frequently involved in carcinoma and tuberculosis, and may form masses which may be mistaken either for independent tumors or outgrowths from other organs. They are sometimes inflamed, and even cause abscess, being mistaken for appendix disease. They become calcareous and by the Rontgen rays may cast shadows which have been mistaken for calculi of the urinary organs.

The mesentery has its vessels sometimes ruptured by violence or blocked by emboli or thrombi. This is likely to cause gangrene of the intestine to which they are distributed. In abdominal operations the greatest care is to be taken not to injure these vessels, and in hemorrhage the least possible amount of ligation is to be done. Obstructions of a mesenteric branch may necessitate the resection of that part of the small intestine which it supplies.

It is particularly important to bear in mind the direction of the mesenteric attachment on account of its influence in directing the course of the blood in cases of hemorrhage. The small intestines are attached at the root of the mesentery like the leaves of a book to its back. Bleeding originating from the right and upper quadrants of the abdomen will pass over the intestines and tend to gravitate toward the right iliac fossa. Bleeding originating from the left and lower quadrants tends to pass under the intestines toward the left iliac fossa. In searching the abdomen through a large median incision for the source of a concealed hemorrhage, the intestines are first to be pushed down and to the left, and the right side of the abdominal wall lifted with retractors. This will expose to view the upper surface of the small intestines, the ascending and transverse colon, the right kidney, liver, stomach, and head of the pancreas. Should additional search be necessary the small intestines are to be raised and turned upward and to the right (Fig. 422), being brought out of the wound if necessary. This will expose the under side of the small intestines and mesentery, the sigmoid flexure, descending colon, left kidney, spleen, and tail of the pancreas, with the left end of the stomach and left lobe of the liver above. The intestines are never to be turned downward to the right nor upward to the left.

The mesentery attains its greatest length, according to Treves, from 6 to 11 feet below the duodenum, where it measures 25 cm. (10 in.) In hernia the mesentery is lengthened to allow of the descent of the gut. Rarely openings are present in the mesentery which may allow the entrance and strangulation of a coil of the intestine.

Fig. 422. - The mesentery is seen running downward toward the right sacro-iliac joint; the index finger is below it and the other three fingers above. The small intestines have been raised on the hand and turned upward thus exposing the pelvis and entire left lower half of the abdomen for examination.