370 RICHARD E. SCAMMON 



pouch and breaks up into five large tubules, the largest of which is 

 directed posteriorly. 



In an embryo of 20.6 mm. (H.E.C. 1494, No. 28, Normal 

 plate series) the hepatic ducts are so completely formed that 

 their origin from pouches and tubule groups would hardly be 

 surmised from the reconstruction of them seen in figure 50. The 

 pars ductus mediana is not separable from the more posterior 

 part of the ductus choledochus and the left part of the pars he- 

 patica mediana and the left lateral pouch form together one duct, 

 the left hepatic, which arises from the lateral surface of the ductus 

 choledochus and curves first laterally and then backward. The 

 distinct angle between the transverse and longitudinal parts of 

 the duct is the point of union of the two elements which form it. 

 The right medial hepatic ramus arises at the union of the left 

 hepatic duct with the ductus choledochus. Immediately to the 

 left of this is a smooth narrow segment of the left hepatic duct 

 which lies between two branches of the left vitelline vein. To the 

 left of this segment lies a dorsal duct, the left medial ramus, 

 and below and lateral to it is the anterior left ramus. These 

 represent the anterior left and left medial tubule clusters respec- 

 tively. The small tubules which are seen in the anterior view of 

 the model arising between these two ducts are probably derived in 

 part from both tubule groups which, it will be remembered, were 

 somewhat fused in earlier stages. 



The right hepatic duct is much shorter than the left. It takes 

 origin from the anterior end of the ductus choledochus and curves 

 backward at once. A very large dorsal ramus arises from its 

 upper surface just distal to its connection with the ductus chole- 

 dochus. This is the anterior right hepatic ramus and corresponds 

 to the tubule group of the same name in younger embryos. Aside 

 from this and one small tubule arising from the anterior surface, 

 the proximal part of the right hepatic duct is smooth. ■ Near its 

 distal end it gives off several minor tubules. The dorsal ones 

 represent the dorsal posterior tubule cluster while the ventral 

 ones are derived from the ventral posterior tubule cluster as is 

 also the most distal part of the duct itself. By this stage all the 

 minor hepatic rami are established and no new tubules arise from 



