DEVELOPMENT OF THE ALIMENTARY TUBE AND APPENDED ORGANS. 353 



mass. A communication is established between the two ducts, and the dorsal 

 duct (Santorini) usually disappears, leaving the ventral (Wirsung) as the per- 

 manent duct opening into the ductus choledochus. In a general way it may be 

 said that the ventral anlage gives rise to the head, the 'dorsal anlage to the body 

 and tail of the pancreas (compare Figs. 316 and 317). 



As the pancreas grows into the dorsal mesentery it comes to lie in the 

 dorsal mesogastrium between the greater curvature of the stomach and the 

 vertebral column, and since the dorsal mesogastrium at first lies in the medial 

 sagittal plane, the pancreas is similarly situated. After the sixth week, how- 

 ever, as the stomach changes its position (p. 337), the pancreas is carried along 



Inf. vena cava 



Mesonephros 



Greater omentum 

 (dorsal mesentery) 



Duodenum 



Right side 



Liver 



Left side 



Fig. 318.— From a transverse section through the region of the duodenum of a pig 

 embryo of 14 mm. Photograph. 



-with the mesogastrium and comes to lie in a transverse plane, with its head to 

 the right and embedded in the bend of the duodenum, and its tail reaching to 

 the spleen on the left. The organ as a whole is at first movable along with the 

 mesentery, but when it assumes its transverse position it lies close to the dorsal 

 abdominal wall. The mesentery then fuses with the adjacent peritoneum 

 (see p. 382), and the pancreas is firmly fixed. 



The connective tissue of the pancreas is derived from the mesodermal tissue 

 of the mesentery. As the processes or buds which form the ducts and terminal 

 tubules grow out from the primary masses, they penetrate the mesodermal 

 tissue and are surrounded by it. Groups of tubules form lobes and lobules, 

 and the entire gland is surrounded by a capsule of connective tissue. 



