i86 



THE ENTODERMAL CANAL AND ITS DERIVATIVES 



which bear the same relation to each other and to new lobules as did the primary branches to 

 the first lobule. This process is repeated until thousands of liver lobules are developed. 



Until the 20 mm. stage the portal vein alone supplies the liver. The hepatic artery from 

 the cceliac axis comes into relation first with the hepatic duct and gall-bladder. Later, it 

 grows into the connective tissue about the larger bile ducts and branches of the portal vein, 

 and also supplies the capsule of the liver. 



The development of the ligaments of the liver is described on p. 200. 



Anomalies of the liver occur chiefly in connection with the gall-bladder and ducts. The 

 gall-bladder may be absent or two may be present. Duplications and absence of the hepatic 

 duct has been observed, also duplication of the cystic duct. In some animals (horse, elephant) 

 the gall-bladder is normally absent. 



f i 



V" 



b J 



Fig. 179. — Diagrams of three successive stages of the portal and hepatic veins in a growing liver, 

 a, Hepatic side; d, portal side; b and c, successive stage of the hepatic vein; e and/, successive stages of 

 the portal vein (Mall). 



THE PANCREAS 

 Two pancreatic anlages are developed almost simultaneously in embryos of 

 3 to 4 mm. The dorsal pancreas arises as a hollow outpocketing of the dorsal 

 duodenal wall slightly cranial to the hepatic diverticulum. At 7.5 mm. it is 

 separated from the duodenum by a slight constriction (Fig. 178 A). The ventral 

 pancreas develops in the inferior angle between the hepatic diverticulum and the 

 gut (Lewis) and its wall is continuous with both. With the elongation of the 

 ductus choledochus it is gradually separated from the intestine. 



The ventral pancreas may arise directly from the intestinal wall. In cases observed by 

 Debeyre, Helly and Kollmann, the anlage was paired and in other embryos a paired structure 

 is indicated. ' 



