234 E. A. BAUMGARTNER 



is a wide cavity. On the external surface there is a sUght dorso- 

 ventral furrow, an indication of the beginning division into 

 lateral and medial rami. 



In an embryo approximately 9 mm. long the right side shows 

 a more marked lateral ramus. The medial still somewhat dorsal 

 ramus is to be seen (fig. 37) . Here the left side shows a marked 

 dorso-medial and a ventro-lateral prolongation. The outer 

 surface of both sides of the organ shows many projections, the 

 beginning of tubules from these main rami. The cystic duct 

 though slightly to the right shows more of a constriction from 

 that side. The anterior lip of the cystic evagination also is 

 very prominent. 



The rami are formed from the early hepatic ducts by a cau- 

 dalward constriction and by elongation. Mitotic figures are 

 to be seen at this stage but are more numerous in later ones. As 

 is true of fishes (Scammon '13) there is a relative and actual 

 reduction in the size of these ducts. 



In another 9 mm. embryo the development of the ducts is 

 seen to have progressed rapidly (fig. 38). Numerous mitotic 

 figures are to be seen in different sections indicating a rapid 

 growth of the ducts. There are distinct right and left hepatic 

 ducts which show a marked growth. There is a medial longitud- 

 inal ridge in the ventral wall of the ductus choledochus indi- 

 cating a caudalward progressing constriction and division (fig. 

 38). The cystic duct {D. cy.) is distinctly differentiated and 

 attached to the right of the beginning constriction in the common 

 duct. It extends ventrally and somewhat towards the right. 

 The right hepatic duct as seen in figure 38, and in a figure of a 

 model of the cavity of ducts (fig. 20) is divided into a lateral and 

 a dorso-medial ramus. The lateral ramus is further divided into 

 lateral dorsal and medial ventral branches. The left ramus also 

 has medial and lateral divisions. 



In embryos from 10 to 12 mm. in length, the trabeculae pre- 

 sent a confusing network. The epithelium of both the hepatic 

 ducts and trabeculae are heavily laden with yolk-granules, and 

 that of the ducts is not yet differentiated into a distinct columnar 

 type. However, the right and left hepatic ducts are clear. In 



