238 



CHORDATE ANATOMY 



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 ahmentary 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 

 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. 



/MESOGASTER 



'GREATER OMENTUM < 



^1^^^ 



|t~-CAECUM-^ 

 j/ APPENDIX--^ j 



SMALL INTESTINE 

 '/-COLON 



•YOLK STALK 



ESOPHAGUS - 



CURVATURE 

 STOMACH 



'— GREATER OMENTUM 



COLON 



CAECUM ^j 

 VPPENDIX -■!^ 



SMALL INTESTINE' 



Fig. 222. — Diagrams illustrating the development of the mesenteries and omentum 

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

 greater omentum. (Redrawn after Hertwig.) 



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 epiploicum into the coelom 

 of the right side. The omentum becomes the seat of deposit of con- 

 siderable fat and serves as a blanket to keep the viscera warm. 



The Liver 



The functions of the Hver are diverse. During early ontogenesis, it 

 forms red blood corpuscles. Later in life, it becomes an agent in the 

 eUmination of blood cells. It transforms both sugar and protein into a 

 polysaccharid, glycogen, which it stores in its cells for later use. It also 



