350 TEXT-BOOK OF EMBRYOLOGY. 



directly continuous with the septum transversum, it is later attached to the 

 liver. In other words it passes between the liver and the lesser curvature of the 

 stomach and also extends along the duodenal portion of the gut for a short 

 distance (Fig. 263). As the stomach turns to the left the ventral mesentery is 

 also drawn toward the left and comes to lie almost at right angles to the sagittal 

 plane of the body, forming the lesser omentum (omentum minus) or the hepato- 

 gastric and hepatoduodenal ligaments of the adult (Figs. 303 and 304). 



The Mesenteries. So long as the intestine is a straight tube, the dorsal 

 mesentery lies in the medial sagittal plane, its dorsal attachment being practi- 

 cally of the same length as its ventral (intestinal) attachment. As development 

 proceeds, the intestine elongates much more rapidly than the abdominal walls, 

 and the intestinal attachment of the mesentery elongates accordingly. When 

 the portion of the intestine to which the yolk stalk is attached grows out into the 

 proximal end of the umbilical cord (p. 307) , the corresponding portion of the 

 mesentery is drawn out with it (Fig. 263). When the intestine returns to the 

 abdominal cavity and forms the primary loop, with the caecum to the right side 

 (p. 308), its mesenteric attachment is carried out of the medial sagittal plane. 

 This results in a funnel-shaped twisting of the mesentery (Figs. 299 and 300). 

 The portion of the mesentery which forms the funnel is destined to become the 

 mesentery of the jejunum, ileum, and ascending and transverse colon, and is 

 attached to the dorsal body wall at the apex of the funnel (Fig. 299, 300, 304). 

 This condition is reached about the middle of the fourth month. 



Up to this time the mesentery and intestine are freely movable, that is, they 

 have formed no secondary attachments. From this time on, as the intestine 

 continues to elongate and forms loops and coils, the mesentery is thrown into 

 folds, and certain parts of it fuse with other parts and with the body wall. 

 Thus certain parts of the intestine become less free or less movable within the 

 abdominal cavity. 



The duodenum changes from the original longitudinal position to a more 

 nearly transverse position and, with its mesentery the mesoduodenum fuses 

 with the dorsal body wall, thus becoming firmly fixed. Since the mesoduode- 

 num fuses with the body wall, the duodenum has no mesentery in the adult. 

 The pancreas, which is primarily enclosed within the mesoduodenum, also 

 becomes firmly attached to the dorsal body wall (compare Figs. 301 and 302). 



The mesentery of the transverse colon, or the transverse mesocolon, which 

 lies across the body ventral to the duodenum (Figs. 300 and 304), fuses with the 

 ventral surface of the latter and with the peritoneum of the dorsal body wall. 

 In this way the dorsal attachment of the transverse mesocolon is changed from 

 its original sagittal direction to a transverse direction (Figs. 302 and 303). The 

 mesocolon itself forms a transverse partition which divides the peritoneal cavity 

 into two parts, an upper (or cranial) which contains the stomach and liver, and 



