THE DIGESTIVE SYSTEM 



321 



part of the ventral mesentery disappears in ontogenesis. The anterior 

 portion which connects stomach, Hver and ventral body wall only is 

 retained. With the differentiation of the successive regions of the ahmen- 

 tary canal corresponding portions of the dorsal mesentery are recognized 

 as mesogaster, mesentery, mesocolon, and mesorectum. The mesenteries 

 serve not only as means of attachment of the intestine to the body wall, 

 but also as a passage for the blood vessels of the alimentary canal. In 

 the adult the mesenteries become very complex in relations as the result 

 of the elongation of the intestine, formation of omenta, and local adhesions. 

 As the stomach develops its greater curvature it rotates on its long 

 axis so that its left side becomes ventral and the right side dorsal. As a 



MESOGASTER 



GREATER OMENTUM ,' 



STOMACH 



DUODENUM-- 



-CAECUM — 

 APPENDIX- 

 SMALL INTESTINE- 

 COLON 



YOLK STALK 



Fig. 268. — Diagrams illustrating the development of the mesenteries and omentum 

 in the human embryo. An arrow marks the opening (foramen of Winslow) of the 

 greater omentLun. (Redrawn after Hertwig.) 



result the dorsal mesogaster is stretched to the left and a pouch or bursa 

 between the mesogaster and the right side of the stomach is formed. 

 The pancreas and spleen which lie in the dorsal mesogaster are also car- 

 ried over to the left side of the body where they form adhesions with the 

 dorsal body wall. As the sacculation of the mesogaster progresses, dorsal 

 and ventral layers become distinguishable. The two-layered sac thus 

 formed grows ventrally and posteriorly between the viscera and the ventral 

 wall of the abdomen as an apron-like membrane, the greater omentum. 

 Much of the original cavity of the omentum is lost through the fusion of 

 dorsal and ventral layers. In the region of the stomach, however, the 

 cavity persists as the bursa omentalis, which opens by the foramen 

 epiploicimi into the coelom of the right side. The omentum becomes the 

 seat of deposit of considerable fat and serves as a blanket to keep the 

 viscera warm. 



