FROM TWELVE TO THIRTY-SIX SOMITES 181 
moses where branches meet, so that a complete ring of anas- 
tomosing columns of hepatic cylinders is rapidly formed around 
the center of the ductus venosus 
(Figs. 103 B and 104, ef. also Figs. 
119 and 120). But the anterior 
and posterior ends of the ductus 
venosus are not yet completely 
surrounded by the basket-work of 
liver substance, owing to the ab- 
sence of any part of the posterior 
diverticulum in its anterior por- 
tion, and of the anterior divertic- 
ulum in its posterior portion. 
The floor of the intestine be- 
tween the anterior and posterior 
liver diverticula is depressed; later 
it becomes separated from the 
intestinal cavity to form a tem- 
porary common bile-duct; which 
then receives the two primary di- 
verticula (Figs. 103B, 104 and 
187). 
The pancreas arises from a dor- 
sal and a pair of ventral primordia. 
The former is an outgrowth of 
the dorsal wall of the intestine 
immediately above the posterior 
liver diverticulum (Figs. 103 B 
and 104). At the 35s stage it is 
a solid thickening of the dorsal 
wall of the intestine of consider- 
able extent; a little later the base 
of the thickening is hollowed out, 
and the free margin sends off solid 
buds into the dorsal mesentery 
Fig. 104. — Reconstruction of the 
liver of the chick at the end of 
the fourth day of incubation. 
(After Hammar. ) 
du., Duodenum. L., Substance 
of liver. Other abbreviations as 
before. 
just behind the stomach. The ventral primordia arise from the 
posterior liver diverticulum in a manner to be described later 
(Chap. X). 
Mid-gut. At the 35s stage the mid-gut is still open to the 
yolk-sac. Its subsequent history is given in Chapter X. 
