372 RICHARD E. SCAMMON 



that structure. This process, illustrated in figures 22, 23, 24, 

 25 and 54, is brought about in part at least by the growth of the 

 internal yolk sac and is discussed in more detail in the section 

 upon the development of the gall bladder. A distinct forward 

 arch appears in the proximal portion of the main hepatic ducts 

 so that instead of entering the ductus choledochus at right angles 

 to its longitudinal axis as in younger stage, they extend backward 

 on either side of it for a short distance and then join with it very 

 obliquely. This arch may be partially brought about by the 

 hepatic ducts being forced forward by the same agency as that 

 influencing the cystic apparatus at this time but probably it is 

 also due in part to the actual shifting backward of the ostia of the 

 hepatic ducts along the ductus choledochus. 



Up to the stage represented by the embryo of 20.6 mm., the 

 hepatic ducts were described with little difficulty for they pursue 

 much the same course in all the specimens which were examined. 

 However, the reduction in size of the distal end of the ductus 

 choledochus and the shiftings which it and the hepatic ducts 

 undergo modify considerably the position of some of the minor 

 ducts and to varying degrees in different specimens. This applies 

 particularly to the anterior left and right lateral rami and the 

 left and right medial rami. The posterior dorsal rami remain 

 fairly constant in position at the juncture of the transverse and 

 posterior parts of their respective trunks, and the posterior ven- 

 tral rami, while giving rise to new short minor sprouts in their 

 course, seem fairly regular. 



Of the several types observed in embryos and specimens of 

 the pup stage, the commonest and simplest one is that in which 

 rotation of the ductus choledochus is present but not extreme 

 a,nd in which the embryonic arrangement of the rami is to a 

 large extent retained. This form is illustrated by the graphic 

 reconstruction of two embryos, one 28 mm. and one 41 mm. in 

 length illustrated in figures 21 and 22. 



The variants from this type so far as observed have been such 

 as might be expected from farther rotation of the anterior part 

 of the ductus choledochus. If this process is extreme all those 

 rami which arise from the anterior surface of the pars hepatica 



