THE LATER DEVELOPMENT OF THE CHICK 333 



the stomach region. This is the region where the great veins 

 are converging toward the heart (ductus venosus, ductus 

 Cuvieri, see below). The anterior liver diverticulum appears 

 some hours before the posterior, and as it grows forward it lies 

 to the left, the later posterior diverticulum then extends 

 rather toward the right side, and although it becomes the 

 larger, it does not grow as far forward as the anterior diver- 

 ticulum. During the third and fourth days both diverticula 

 branch and anastomose, forming a network of liver tissue 

 (Fig. 123, B] around the large vein (ductus venosus). The 

 liver soon enlarges enormously and early becomes very vas- 

 cular, through the development of vessels connecting with 

 the ductus venosus, directly among the meshes of the liver 

 substance. 



The bile duct and gall-bladder arise from the short ventral 

 region of the gut between the two liver diverticula; this re- 

 gion grows out carrying with it the openings of the diverticula, 

 which thus come to open into a common chamber, the ductus 

 choledochus or common bile duct. The gall-bladder develops 

 in connection with the duct of the posterior liver diverticulum. 

 The common bile duct is a transitory structure, and when it 

 disappears the two liver (bile) ducts again open separately into 

 the gut. 



About the same time and in the same general region as the 

 liver, the pancreas develops, from three separate diverticula. A 

 dorsal median diverticulum grows out, directly opposite the pos- 

 terior liver diverticulum, about the end of the third day. Right 

 and left ventral pancreatic diverticula appear later, pushing 

 out from the walls of the ductus choledochus close to the gut- 

 wall. When the ductus choledochus disappears these pan- 

 creatic rudiments open separately into the gut. As these 

 diverticula enlarge they branch distally and by a budding proc- 

 ess form the glandular units of the organ. The bodies of the 

 three rudiments finally join, forming a common gland, al- 

 though their ducts remain opening separately near the two 

 bile ducts. 



