BODY CAVITIES, DIAPHRAGM AND MESENTERIES 



193 



The mesentery of the intestine is carried out into the umbilical cord between the 

 Hmbs of the intestinal loop. When the intestine elongates and its loop rotates, 

 the caecal end of the large intestine comes to he cranially and to the left,' the small 

 intestine caudally and to the right, the future duodenum and colon crossing in 

 close proximity to each other (Fig. 179). On the return of the intestinal loop 

 into the abdomen from the umbiHcal cord, the caecal end of the colon lies to the 

 right and the transverse colon crosses the duodenum ventrally and cranially 

 (Fig. 203 A). The primary loops of the small intestine he caudal and to the left 

 of the ascending colon (Fig. 203 B). There has thus been a torsion of the mesen- 

 tery about the origin of the superior mesenteric artery as an axis. From this focal 



Lesser omentum 



•Slomach 



Dorsal mesogaslriiim. 



Ccccuni 



Alesi'iitti \ 

 Alesorci'lHni 



Iliac mesocolon 

 A B 



Fig. 203. — Diagrams showing the development of the mesenteries in ventral view (modified after 

 Tourneux). * Cut edge of greater omentum; a, area of ascending mesocolon fused to dorsal body wall; 

 b, area of descending mesocolon fused to dorsal body wall. Arrow in omental bursa. 



point the mesentery of the small intestine and colon spreads out fan-like. The 

 mesoduodenum is pressed against the dorsal body wall, fuses with its peritoneal 

 layer, and is obhterated (Fig. 202) . Since the transverse colon lies ventral to the 

 duodenum it cannot come into apposition with the body wall; where its mesentery 

 crosses the duodenum it fuses at its base with the surface of the latter and of the 

 pancreas. Its fixed position now being transverse instead of sagittal, the mesen- 

 tery is known as the transverse mesocolon. The mesentery of the ascending colon 

 is flattened against the dorsal body wall on the right and fuses with the peritoneum 

 (Fig. 203). Similarly, the descending mesocolon is apphed to the body wall of 

 the left side. There are thus left free : (1) the transverse mesocolon ; (2) the mesen- 

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