THE PERITONEUM 



1247 



The alimentary tube, now in its simplest form, is nearly straight and may be 

 divided into three portions: (a) the foregut between the pericardium and noto- 



Midbrain. 

 Cerebellum.-* ^^ ! iQptic vesicle. 



Buceopharyngeal 

 membrane. 



Pharynx. - 

 Auditory pit."' 



Aortic bulb. 



Stomach. L 



Cloacal dilatation- 4- 

 of hind-gut. 



Allantoic stalk 

 Umbilical vein 



Stomodseum. 



Ventricle 

 /' of heart. 



.. Liver. 



^Mid-gut and yolk 

 stalk. 



^Hind-gut. 



Allantois. 

 -Umbilical artery. 



FIG. 964. Human emfiryo, about fifteen days old. Brain and heart represented from right side; alimentary 

 canal and yolk sac in mesal section. (After His.) 



chord; (6) the midgut, opening directly into the yolk sac; and (c) the hindgut, 

 contained within the caudal fold. The passage between the midgut and the 



(Esophagus. 



Bile duct. 



V-shaped loop 

 of mid-gut. 



Vitello-intestinal duct: 

 Cloaca. 



Pancreas. 



ng. 



^Trachea. 



Lung. 

 (Esophagus. 



Stomach. 



FIG. 965. Front view of two successive stages in the development of the alimentary canal. (His.") 



yolk sac is at first relatively wide, but it is subsequently narrowed and lengthened 

 to become the tubular vitelline duct (to wholly disappear eventually). 



