DEVELOPMENT OF THE FECUNDATED EGG. 513 



A protuberance is formed upon this common trunk which 

 serves for a vascular blood gland, or the liver (glycogenic 

 portion of the liver, see pp. 232 and 265) ; so soon as the 

 liver is formed around the common trunk of the umbilical 

 and mesenteric veins, each of these veins sends into this 

 glandular protuberance, or rather pouch, vascular ramifica- 

 tions ; those which come from the mesenteric veins form the 

 afferent hepatic veins, and those which come from the com- 

 mon trunk form the efferent hepatic veins. In this way, 



Fig. 147. Diagram of the development of the omphalo-mesenteric, umbilical, 

 and portal veins.* 



and as more clearly indicated in the Fig. 147 (B), the mesen- 

 cenc vein and its afferent hepatic veins form the portal sys- 

 tem, whose veins ramify in the liver and whose subsequent 

 union comprises the efferent hepatic veins; finally, these 

 Utter conduct to the common and free trunk beyond the 



* A. Period corresponding with the close of the primary and commencement 

 of the second circulation. 1, Common trunk of the omphalo-mesenteric veins. 

 2, Right omphalo-mesenteric vein. 3, The left. 4, Common trunk of the um- 

 bilical veins in process of formation. 5, The right umbilical vein. 6, The 

 left. 



B. Formation of the liver. 1, Permanent mesenteric vein (future portal 

 vein). 2, 3, Representing the place of the atrophied omphalo-mesenteric veins. 

 5, Right umbilical vein undergoing a process of atrophy. 6, Permanent umbili- 

 cal vein. 7, Canal of Cuvicr (duct us Cuvieri). 8, Anterior or superior cardinal 

 veins. 9, Posterior or inferior cardinal veins, or jugular veins. 10, Liver, with 

 the afferent and efferent veins. 



C. Formation </' the venaporfa and canalis Arantii sen ductus venosus (per- 

 fected state of the placental circulation). 1, Remains of the omphalo-mesenteric 

 (omphalo-mesaraic) vein. 13, Mesenteric vein (portal vein). 6, Umbilical vein. 

 4, Ductus venosus sen canalis Arautii. 12, Afferent hepatic veins. 11, Efferent 

 hepatic veins. (Kulliker.) 



