1250 



THE ORGANS OF DIGESTION 



The stomach and intestine, with their mesenteries, undergo changes of position 

 determined by several growth factors, such as the elongation of the intestine, and 

 the development of such organs as the liver, pancreas, and spleen. Such devel- 

 opmental changes, with subsequent displacements, adhesions, and absorptions, 

 serve to form all the mesenteries, omenta, and peritoneal folds of the adult, so 

 that, while in the primitive condition the intestinal tube is suspended by a dorsal 

 mesentery and freely movable, certain portions of it become later, by secondary 

 adhesion, firmly connected with the parietes (retroperitoneal) or with other por- 

 tions of the tract. 



Rotation of Stomach and Intestine. The stomach rotates so that its greater 

 (dorsal) curvature with the attached dorsal mesogastrium is carried downward 

 and to the left, so that the right surface of the stomach is now directed backward 

 and the left surface forward (ventrad) a change in position which explains 

 why the left vagus nerve is found on the front of the 

 stomach and the right vagus on the back of it. As the 

 stomach rotates, the dorsal mesogastrium is necessarily 

 elongated; this elongation is, however, augmented in 

 further development, so that a large pouch, the bursa 

 omentalis or lesser sac is formed. The entrance to this 

 pouch constitutes the future foramen of Winslow. 

 The duodenum, developed from that part of the tube 

 which immediately succeeds the stomach, undergoes 



Septum transversum. 



Liver. 



Mesofiastrium 

 (ventral part). | 



Umbilical vein. 



Umbilical cord 



Aorta. 



Mesogastrium 

 ' (dorsal part). 



Stomach. 



Intestinal 



V-shaped loop. 

 Mesentery, 



- Colon. 



FIG. 970. The primitive mesentery of a six weeks' human embryo, half 

 schematic. (Kollmann.) 



FIG. 971. Final disposition 

 of the intestines and their vas- 

 cular relations. A. Aorta. H. 

 Hepatic artery. S. Splenic ar- 

 tery. M, Col. Branches of supe- 

 rior mesenteric artery. m, m'. 

 Branches of inferior mesenteric 

 artery. (Jonnesco.) 



little elongation. It is at first suspended by a mesentery (mesoduodenum) and 

 projects forward in the form of a loop. The loop is subsequently displaced 

 backward by the transverse colon, so that the right surface of the mesoduodenum 

 is swung back, and, adhering to the parietal peritoneum partly in front of the 

 right kidney, is obliterated; in this way the duodenum, together with the pancreas 

 which has invaded the dorsal mesoduodenum, become retroperitoneal. It is 

 further fixed in position by the liver and pancreas which arise as diverticula from 

 it. The liver, developing between the layers of the ventral mesogastrium, comes 

 to occupy the upper right portion of the abdominal cavity, and thus reduces the 

 entrance to the omental bursa to the small foramen of Winslow. 



The remainder of the alimentary canal becomes elongated, and as a consequence 

 the tube becomes complexly coiled on itself, and this elongation demands a 

 corresponding increase in the width of the intestinal attachment of the mesentery, 

 which becomes folded. 



