362 RICHARD E. SCAMMON 



The mesial surfaces of the lateral pouches are smooth except 

 for some minor fissures and the gutter like spaces between them 

 and the pars mediana are occupied by mesenchyma and the vitel- 

 line veins. The lateral surface of each pouch is almost obscured 

 by the numerous hepatic tubules which arise from it. The dorsal 

 growth of the pouches so evident in early stages has now come to 

 an end and their dorsal margins hardly extend above the ventral 

 surface of the stomach as is seen in figures 41 and 42. A number 

 of large trunk-tubules arise from them. As in the pars hepatica 

 mediana all the tubules of the lateral pouches tend to gather in 

 certain fairly well defined groups. These consist, on either side, 

 of an anterior and a posterior group, and the latter is less definitely 

 subdi\'ided into a dorsal and a ventral cluster. The tubules of 

 the anterior groups spring from the dorsal half of the anterior 

 part of the lateral pouch leaving a ventral area below which is 

 smooth or occupied only by small tubules in the process of forma- 

 tion. The posterior group is much larger and its two subdivi- 

 sions occupy the entire posterior half and hinder margin of the 

 pouch. As will be seen from figure 41, these groups are not com- 

 pletely separated, as small and less developed tubules intervene 

 in some places. The formation of these minor tubules continues 

 until a much later period. The tubule groups of the anterior 

 part of the left lateral pouch and of the left side of the pars 

 hepatica mediana lie much closer together than those of the 

 opposite side. 



This early arrangement of the hepatic tubules into groups is of 

 much importance for, as has been stated, while the main hepatic 

 ducts are produced b}^ the elongation and narrowing of the 

 caliber of the lateral pouches, each group of tubules becomes iso- 

 lated by the formation of a common stalk which later develops 

 into one or more rami of the minor hepatic ducts. The arrange- 

 ment of the tubule groups is expressed in tat)ular form in table 1 . 



A reconstruction, illustrated in figures 43, 45 and 46 of an em- 

 bryo but 0.5 mm. longer than the preceding but which resembles 

 in general anatomy the average embryo of 18 mm., shows more 

 clearly the process of duct formation. The common bile duct is 

 now three times as long as its greatest diameter and the pars due- 



