Henry Gray (18251861). Anatomy of the Human Body. 1918.
mesogastria are now directed backward, and the left forward. In this way a pouch, the bursa omentalis, is formed behind the stomach, and this increases in size as the digestive tube undergoes further development; the entrance to the pouch constitutes the future foramen epiploicum or foramen of Winslow. The duodenum is developed from that part of the tube which immediately succeeds the stomach; it undergoes little elongation, being more or less fixed in position by the liver and pancreas, which arise as diverticula from it. The duodenum is at first suspended by a mesentery, and projects forward in the form of a loop. The loop and its mesentery are subsequently displaced by the transverse colon, so that the right surface of the duodenal mesentery is directed backward, and, adhering to the parietal peritoneum, is lost. The remainder of the digestive tube becomes greatly elongated, and as a consequence the tube is coiled on itself, and this elongation demands a corresponding increase in the width of the intestinal attachment of the mesentery, which becomes folded.
FIG. 983 Front view of two successive stages in the development of the digestive tube. (His.) (See enlarged image)
FIG. 984 The primitive mesentery of a six weeks human embryo, half schematic. (Kollmann.) (See enlarged image)
FIG. 985 Abdominal part of digestive tube and its attachment to the primitive or common mesentery. Human embryo of six weeks. (After Toldt.) (See enlarged image)
At this stage the small and large intestines are attached to the vertebral column by a common mesentery, the coils of the small intestine falling to the right of the middle line, while the large intestine lies on the left side. 1
The gut is now rotated upon itself, so that the large intestine is carried over in front of the small intestine, and the cecum is placed immediately below the liver; about the sixth month the cecum descends into the right iliac fossa, and the large intestine forms an arch consisting of the ascending, transverse, and descending portions of the colonthe transverse portion crossing in front of the duodenum and lying just below the greater curvature of the stomach; within this arch the coils of the small intestine are disposed (Fig. 988). Sometimes the downward
Note 1. Sometimes this condition persists throughout life, and it is then found that the duodenum does not cross from the right to the left side of the vertebral column, but lies entirely on the right side of the median plane, where it is continued into the jejunum; the arteries to the small intestine (aa. intestinales) also arise from the right instead of the left side of the superior mesenteric artery. [back]