Frank A. Stromsten 



469 



present it is found further craniad and opens into the common hepatic 

 vein. As sliown by Fig. G, one of tlicse bi-anches is given off from the 

 mesenteric portal almost directly opposite the opening of the gastric 

 vein. This branch persists in the adult form where it functions as the 

 chief lateral branch of the mesenteric portal, the right hepatic advehent 

 branch of Fig. 1. It is possible that the other l)ranches are also retained, 

 in part at least, as branches of the mesenteric portal of the adult, but it 

 is not possible to trace their subsequent development with certainty. 



The right omphalo-mesenteric vein has split still further craniad than 

 in the previous stage, so that, as shown in Fig. G, there is a small portion 



VERTEBRAL VEIN 

 "J^-^. - \ - CHORDA 



RIGHT HEPATIC— f 



MESENTERIC PORTAL 



GALL BLADDER 

 RIGHT UMBILICAL 



POSTCARDINAL 

 AORTA 

 ESONEPHROS 



--STOMACH 



GASTRIC VEIN 



LEFT UMBILICAL 

 INTESTINE 



Fig. 7. Cross-section of a 12 mm. embryo of Kinosternon pennsylvanicum, 

 at the level where the postcava enters the liver, showing the curved anasto- 

 mosis (A) between the hepatic and mesenteric portal veins and the opening 

 of the gastric vein into the mesenteric portal. The portal vein of Bojanus is 

 not yet formed. 



(Z) of the left branch next to the common hepatic vein that is not yet 

 broken up into sinusoids. A part of this short, wide stem is retained in 

 the adult as the terminal portion of the left hepatic revehent vein, the 

 other part of this hepatic vein is, as we shall see, developed from the 

 umbilical vein. A part of the left revehent vein, therefore, as well as 

 nearly the entire anlage of the right hepatic vein, is split off from the 

 right omphalo-mesenteric vein. 



Further changes in the derivatives of the omphalo-niesenterics. — The 

 right hepatic and the mesenteric portal veins are becoming more and 

 more separated. The curved anastomosing branches which were so promi- 

 nent in the 12 mm. stage begin to break up in the 13 mm. stage at the 



