CHAPTER XVIII. 



THE ORGANS OF DIGESTION. 



Development of the Liver. — The human liver, in its develop- 

 ment, repeats the forms met with in ascending the animal scale. 

 In Amphioxus the liver is merely a caecal diverticulum of the 

 digestive canal ; in amphibians the liver is a compound tubular 

 gland — the hepatic cells being arranged in cylinders round the 

 bile ducts. In birds and mammals the tubular arrangement is 

 lost and the lobular form substituted. 



7st aortic arch 



dorsal aorta 



I 



transuerse sinus 



left duct of Cuuier 



tpusi. menu-/ 



\cardium /Jung bud in mesentery 

 dorsal mesogast. 

 torn. 



art meso-card. 



con. arter. 

 pericard.' sinus uenosus. 



amnion 



w 



^^—uitelline uein 

 liuer bud 

 ^'yolk sac. 



•ventral mesentery 



septum transu. 



Fig. 212.— The Mesentery of the Fore-gut and its Contents, -viewed from the left 

 side (schematic). 



To understand the development of the liver, the condition of 

 parts at the commencement of the third week must be studied. 



