ALIMENTARY TRACT AND ITS APPENDAGES 321 



vessels that empty into the meatus, and thus appear as branches 

 of the latter. 



The gall-bladder is a very early formation, arising from the 

 hindermost portion of the posterior hepatic diverticulum, as a 

 distinct bud about the stage of 68 hours (Fig. 103), and forming 

 a pyriform appendage at 84 hours. It may reasonably be re- 

 garded as derived from the most posterior portion of the prim- 

 itive hepatic gutter, an interpretation that agrees with the 

 condition found in more primitive vertebrates. 



At the stage of 68 hours (cf. Fig. 103B), the anterior and 

 posterior diverticula proceed from a common depression of the 

 ventral wall of the duodenum, the ductus choledochus. By 

 means of an antero-posterior constriction, the latter becomes 

 much more clearly defined as development proceeds (Fig. 187); 

 there arise from it also the right and left ventral primordia of 

 the pancreas (see below), so that it receives at this stage four 

 main ducts, viz.: the right and left ventral pancreatic diverticula 

 and the cephalic and caudal hepatic diverticula. On the sixth 

 day these four ducts obtain independent openings into the duo- 

 denum and the common bile duct thus ceases to exist. The 

 relations thus established are practically the same as in the 

 adult. 



As the caudal hepatic diverticulum grows out it carries the 

 attachment of the gall-bladder with it, so that the latter is then 

 attached to the caudal diverticulum, which is thus divided in 

 two parts, a distal or ductus hepato-cysticus, and a proximal or 

 ductus cystico-entericus. That portion of the liver arising from 

 the cephalic diverticulum is thus without any connection with 

 the gall-bladder. There seem, however, to be anastomoses 

 between the ductus hepato-cysticus and the original cephalic 

 duct (ductus hepato-entericus) in the adult, lying in the com- 

 missure of the liver; the embryological origin of these appears, 

 however, to be unknown. In the course of the development, 

 the openings of the two original ducts into the duodenum come 

 to lie side by side instead of one behind the other, and the original 

 cephalic duct (ductus hepato-entericus) appears to be derived 

 mainly from the left lobe, and the ductus cystico-entericus mainly 

 from the right lobe of the liver. The actual distribution is, how- 

 ever, by no means so simple; the mode of development of the 

 lobes of the liver (see below) would explain a preponderant dis- 



