472 



Anatomy nnd Dcvclopiiiont of Veins of Chclonia 



earlier; in fact, it appears to occur, according to Hochstetter, before the 

 right vein has been broken np by the hepatic tubules. The postabdom- 

 inals now open into the iliacs instead of into the postcardinals. 



The backward shifthtg of the point where the vmhiticaJ reins enter the 

 liver, and the formation of the first anlage of the left hepatic revehent 

 vein. Embryo of about 12 mm. — Both umbilical veins, as we have seen, 

 now send branches through the liver to the common hepatic vein (Fig. 6). 

 The portion of the left umbilical vein in the body-wall craniad of its 

 hepatic branch has completely degenerated. The right vein, on the 

 other hand, still retains for a short time its connection with the sinus 



VERTEBRAL VEIN 

 CHORDA 



MESONEPHROS 

 SUBCARDINAL 



RIGHT HEPATIC 



MESENTERIC PORTAL 

 GALL BLADDER 



POSTCARDINAL 



UBCARDINAL 

 GENITAL GLAND 



PANCREAS 

 LEFT UMBILICAL 

 EDIAN VEIN 



RIGHT UMBILICAL 



Fig. 8. Cross section of a 13 mm. embryo of Kinosternon pennsylvaniciim. 



venosus, or, more accurately speaking, with the terminal portion of the 

 common hepatic vein (Fig. 6). Before, however, the 12.5 mm. stage is 

 reached there is no longer any direct connection between the umbilical 

 veins and the sinus venosus, so that all of the blood from these veins 

 must pass through the liver in order to reach the heart. 



The continued backward growth of the folds of the lateral body-walls 

 that go to form the dorsal pericardium causes more and more of the 

 umbilical vein of each side to lie l)etween the liver and the heart. In 

 the case of the left vein, this results in a shifting backward of the point 

 where this vein enters the liver and a consequent atrophy of the vein 

 craniad of this point. The left umbilical vein does not form an entirely 

 new path through the liver ; on the contrary, only that portion marked X 



