284 RICHARD E. SCAMMON 



along on the lateral surfaces of lateral hepatic pouches have 

 formed a vascular plexus consisting of several large sinuses inter- 

 rupted by small lacunae. In the drawing the omphalo-mesenteric 

 veins, properly speaking, are represented in solid black and the 

 sinus venosus and the veins developed from it in stipple. The 

 posterior part of the omphalo-mesenteric veins may now be called 

 'hepatic-portal' veins, this being the term commonly used to 

 designate them in the adult, while the veins which are efferent 

 in their drainage will be designated by the term hepatic veins, 

 which is the name applied to them in works on adult anatomy. 



In the stage just described tubules have formed only on the 

 lateral surfaces of the hepatic pouches. Soon thereafter tubule 

 formation, takes place with great rapidity along the margins of 

 the pouches and from the pars hepatic medialis as well. The 

 latter process results in breaking up the clear passageway of the 

 blood along the left omphalo-mesenteric vein to the sinus venosus 

 and in place of this one discrete passage there are formed a number 

 of small irregular venous channels which pass from the posterior 

 portions of the omphalo-mesenteric veins (hepatic-portal veins) 

 in among the tubules and join the hepatic veins. 



At this time there is a marked growth of the posterior lobes 

 of the liver which brings about several changes in the position of 

 the venous trunks. These may be seen by comparing figures 

 11 B and 11 C which are graphic reconstructions of embryos 

 18 mm. and 41 mm. long respectively. The branches of the 

 early hepatic-portal vein which extend backward along the inner 

 surface of the posterior lobes assume more and more importance, 

 becoming in the later stage the posterior continuations of the 

 main trunks of the vein. The former main trunks which extended 

 forward are relatively reduced in size and appear as branches of 

 these posterior vessels. At the same time the sinus venosus 

 becomes more completely separated from the liver as the septum 

 transversum is formed and the lateral hepatic efferent trunks 

 converge towards the middle line. In so doing they take up 

 the two larger venous radicles which formerly lay medial to them 

 and represented the remains of the extreme anterior ends of the 

 former omphalo-mesenteric veins. Thus these vessels, as may 



