1202 



EMBRYOLOGY. 



mesentery of the duodenum, in which the rudiment of the pancreas is enclosed, dis- 

 appears, and so this part of the gut becomes fixed to the posterior abdominal wall, 

 and the pancreas lies entirely behind the peritoneal membrane. The mesenteries 

 of the ascending and descending parts of the colon disappear in the majority 

 of cases, while that of the small intestine assumes the oblique attachment charac- 

 teristic of its adult condition. 



I Aorta. 



Anterior part of mesogastrium. ~& 



'Spleen. 

 'Mesogastrium. 

 -C'celiac axis. 



perior mesenteric 

 artery. 



';gj&?--Jnferior mesenteric artery. 



-llind-yut. 



FIG. 764. Abdominal part of alimentary canal and its attachment to the primitive or common mesentery 

 Human embryo of six weeks. (After Toldt.) (From Kollmann s Entwickelungsyeschichte.) 



Duodenum. 



Small 

 intestine. 



Yolk-stalk., 



Rectum. 



Yolk-stalk. 



Rectum. 



FIG. 765. Illustrating two stages in the development of the human alimentary canal and its mesentery. 

 The arrow indicates the entrance to the bursa omentalis. 



The small omentum is formed by a thinning of the mesoblast or anterior 



ill 



primitive mesentery, which attaches the lesser curvature of the stomach to the 

 anterior abdominal wall. By the subsequent growth of the liver this leaf of 

 mesoblast is divided into two parts, viz., the small omentum between the stomach 

 and liver, and the falciform ligament between the liver and the abdominal wall 

 and Diaphragm (Fig. 767). 



The anus is developed as a slight invagination of the epiblast a short distance 



