THE PERITONEUM 



1251 



Rotation of the Intestine. At an early stage the small and large intestines are 

 attached to the dorsal wall of the abdomen by a common mesentery, the coils 

 of the small intestine falling to the right, while the large intestine lies on the left 

 side. 1 



The gut now becomes 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, 2 

 and the large intestine now forms an arch consisting of the ascending, transverse, 

 and descending portions of the colon the 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 (Figs. 968 and 9G9). The 



Cecum 



Vitclline Duct 



Fi<;. 972. Torsion of the umbilical loop. 

 Initial position. (Jonnesco.) 



FIG. 973. Torsion of the umbilical loop. 

 Acquired position. (Jonnesco.) 



intestine in its rotation twists the mesentery in a funnel-shaped manner, so that 

 the original right leaf of the mesentery of the small intestine has become the left, 

 and vice versa. The mesentery of the small intestine assumes the oblique attach- 

 ment characteristic of its adult conditions. All divisions of the large intestine 

 are at first freely movable, being suspended by a free mesocolon; but subsequently 

 the ascending and descending portions become fixed retroperitoneal structures 

 in consequence of adhesion of the opposed surfaces of the ascending and descending 

 mesocolons and of the dorsal parietal peritoneum. Occasionally the descending 

 mesocolon, more rarely the ascending, persists so that the bowel is more or less 

 movable in these divisions. The sigmoid colon usually remains movable through- 

 out life. 



The omental bursa, which at first reaches only as far as the greater curvature 

 of the stomach, grows downward as a double-layered, pouch-like fold, the interior 

 layer derived from the right leaf of the primitive mesogastrium, its exterior layer 



1 Sometimes this condition persists throughout life, and it is then found that the duodenum does not cross 

 from the right to the leftside of the vertebral column, but lirs entirely on the right side of the mesal plane, where 

 it is continued into the jejunum; the arteries to the small intestine (rami intestini tenuis) also arise from the 

 right instead of the left side of the superior mesenteric artery. 



2 Sometimes the downward progress of the cecum is arrested, so that in the adult it may be found lying im- 

 mediately below the liver instead of in the right iliac region. 



