TRANSVERSE SECTIONS 



117 



Dnephroi and the posterior cardinal veins are connected with the mesonephric sinu- 

 soids. To the median side of the right mesonephros shows the right subcardinal vein. From the 

 dorsal attachment of the liver there is continued down into this section a ridge on the dorsal 

 body wall just to the right (left of figure) of the mesentery. In this ridge lies a small vein 

 which connects cranially with the liver sinusoids, caudally with the right subcardinal vein. 

 As it later forms a portion of the inferior vena cava, the ridge in which it lies is termed the 

 plica vencK caves or caval mesentery. The right dorsal lobe of the liver contains a large blood 

 space into which opens the portal vein. The duodenum has curved ventral to the position 

 occupied by the stomach in the previous section. There is given off from it ventrad and to 

 the right the hepatic diverticulum. In the sections higher up small ducts from the liver tra- 

 beculae may be traced into connection with it. In the left ventral lobe of the liver, a large 

 blood space indicates the position of the left umbilical vein on its way to the ductus venosus. 



Mvoft 



Dorsal aorta 



R. post, cardinal 

 Vein 



R. umbilical 

 Vein 



Spinal cord 



L. post, cardinal 

 Vein 



Mesonephros 

 Upper I'imb bud 



Mesentery 



Dorsal pancreas 

 LviTelline vein 



Duodenum 

 L.umbHical Vein 



Distal end 

 hepatic diverticulum 



FIG. 108. Transverse section through the dorsal pancreas of a 6 mm. pig embryo. X 26.5. 



Transverse Section through the Dorsal Pancreas (Fig. 108). At this level the 

 upper limb buds still show, the mesenephroi are larger and marked by their large glomeruli. 

 The right posterior cardinal vein is broken up into mesonephric sinusoids. The vein in the plica 

 venae cavae will, a few sections lower, connect with the right subcardinal vein. The anlage of 

 the dorsal pancreas is seen extending from the duodenum dorsad into the mesenchyme of the 

 mesentery. It soon bifurcates into a dorsal and right lobe, of which the latter is slightly 

 lobulated. Ventro-lateral to the duodenum, the anlage of the ventral pancreas is seen cut 

 across. It may be traced cephalad in the series to its origin from the hepatic diverticulum. 

 To the right of the ventral pancreas (left of figure) lies the portal vein (portion of right vitelline). 

 To the left of the dorsal pancreas is seen the remains of the left vitelline vein. The ventral 

 lobes of the liver are just disappearing at this level. In the mesenchyme which connects 

 the liver with the ventral body wall lie on each side the umbilical veins, the left being the 

 larger. Between the veins is the extremity of the hepatic diverticulum. The body wall is 

 continued ventrad to form a short umbilical cord. 



