380 



TEXT-BOOK OF EMBRYOLOGY. 



The Greater Omentum and Omental Bursa. A small part of the gut 

 caudal to the diaphragm is destined to become the stomach, and the portion of 

 the mesentery which attaches it to the dorsal body wall is known as the dorsal 

 mesogastrium (Fig. 301). The latter is inserted along the greater curvature of 

 the stomach and lies in the medial sagittal plane so long as the stomach lies in 

 this plane. When the stomach turns so that its long axis lies in a transverse 

 direction and its greater curvature is directed caudally (p. 337), the dorsal 

 mesogastrium changes its position accordingly. From its attachment along the 

 dorsal body wall it bends to the left and then ventrally to its attachment along 

 the greater curvature of the stomach. Thus a sort of sac is formed dorsal to 

 the stomach (Figs. 337 and 338). This sac is really a part of the abdominal or 



Stomach 



Yolk stalk 



Rectum 



FIG. 337. FIG. 338. 



FIG. 337. Diagram of the gastrointestinal tract and its mesenteries 



at an early stage. Ventral view. Hertwig. 

 FIG. 338. Same at a later stage. Hertwig. 

 The arrow points into the bursa omentalis. 



peritoneal cavity and opens toward the right side. The ventral wall is formed 

 by the stomach, the dorsal and caudal walls by the mesogastrium. The cavity 

 of the sac is the omental Tmrsa (bursa omentalis) ; the mesogastrium forms the 

 greater amentum (omentum majus) . The opening from the bursa into the general 

 peritoneal cavity is the epiploic foramen (foramen of Winslow). (Fig. 314.) 



From the third month on, the greater omentum becomes larger and gradually 

 extends toward the ventral abdominal wall, over the transverse colon, and then 

 caudally between the body wall and the small intestine (Figs. 339 and 340). 

 The portion between the body wall and intestine encloses merely a flat cavity 

 continuous with the larger cavity dorsal to the stomach. From the fourth 

 month on, the omentum fuses with certain other structures and becomes less 

 free. The dorsal lamella fuses with the dorsal body wall on the left side and 



