THE ESOPHAGUS, STOMACH AND INTESTINE 



171 



The Stomach. -The stomach appears in embryos of 4 to 5 mm. as a 

 laterally flattened, fusiform enlargement of the fore-gut caudal to the lung 

 anlages (Figs. 177 and 178). Its epithelium is early thicker than that of 

 esophagus and is surrounded by a heavy layer of splanchnic mesoderm. 

 It is attached dorsally to the body wall by its mesentery, the greater 

 omentum, and ventrally to the liver by the lesser amentum (Fig. 190 B}. 

 The dorsal border of the stomach both bulges locally to form the fundus, 

 and also grows more rapidly than the ventral wall throughout its extent, 

 thus producing the convex greater curvature. The whole stomach be- 

 comes curved and its cranial end is displaced to the left by the enlarging 



Pharynx 

 Root of tongue 



Thyreoid 

 Tip of tongue 



Rathke's pouch 

 Trachea 

 Stomach 



Liver 

 Dorsal pancreas 



Hepatic diverli- 

 culum 



Yolk stalk 



Allantois 



Mesonephric duct 



Cloaca 



Hind-gut 



FIG. 177. Median sagittal section of a 5 mm. human embryo, to show the digestive canal 



(modified after Ingalls). X 14. 



liver (Fig. 168). This forms a ventral concavity, the lesser curvature, and 

 produces the first flexure of the duodenum. 



The rapid growth of the gastric wall along its greater curvature also 

 causes the stomach to rotate upon its long axis until its greater curvature, 

 or primitive dorsal wall, lies to the left, its ventral wall, the lesser curvature, 

 to the right (Fig. 201). The original right side is now dorsal, the left 

 side ventral in position, and the caudal, or pyloric end of the stomach is 

 ventral and to the right of its cardiac, or cephalic end. The whole organ 

 extends obliquely across the peritoneal cavity from left to right (cf . Fig. 

 138). The change in position progresses rapidly and is already completed 

 early r in the second month (12 to 15 mm.). The rotation of the stomach 

 explains the asymmetrical position of the vagus nerves of the adult organ, 



