DEVELOPMENT OF THE ELASMOBRANCH LIVER 349 



shallow groove on the left hand side while on the right they form 

 a smooth somewhat convex surface. Posteriorly the median 

 hepatic pouch is continuous with a short segment of the gut which 

 in turn becomes attached to the yolk stalk. The para-archen- 

 teric grooves are still distinguishable and mark the plane of union 

 between the hepatic anlage and the gut (fig. 8, A, B and C,-P- 

 arch. g.) . Two parts can be distinguished in the median pouch, an 

 anterior one which projects a little in front of the anterior end of 

 the attachment of the lateral pouches, and a posterior part which 

 is directly continuous with the former and from which the lateral 

 pouches and the gall bladder take origin. Although these divi- 

 sions are not sharply marked off at present, they later become 

 quite distinct. The anterior one from its later history may be 

 called the pars hepatica mediana because it shares with the 

 lateral pouches or pars hepatica lateralis in the formation of 

 hepatic ducts and trabeculae. The posterior later develops into 

 a part of the ductus choledochus and may be called the pars 

 ductus mediana in distinction to the anterior and to the pars 

 ductus lateralis formed from the posterior portions of the original 

 hepatic diverticula. The upper surface of the posterior part 

 or pars ductus mediana of the median pouch lying on either side 

 of this dorsal connection with the gut already shows a peculiar 

 modeling indicative of the course which will be eventually taken 

 by the ductus choledochus (fig. 28) . There is a marked expansion 

 which extends from the right anterior angle of the median pouch 

 obliquely backward to the posterior left corner. The anterior, 

 i.e., right portion of this swelling is the more marked. From the 

 posterior edge of the middle pouch this expansion is continued 

 backward into the mid gut as a symmetrical lateral expansion of 

 the ventral part of the 'connecting piece' between the hepatic and 

 stomach anlagen above it to the yolk-stalk and overlying gut. 

 As seen from their position these lateral expansions are the 

 remains of the posterior ends of lateral hepatic diverticula or 

 pars ductus lateralis (fig. 8, C). Thus there can already be recog- 

 nized two distinct parts of the ductus choledochus : an anterior 

 asymmetric portion and a posterior part which is symmetrically 

 placed. 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 14, NO. 3 



