The human embryo begins life with two ducts in the pancreas, these are the ventral duct and the dorsal duct. Normally, the two ducts will fuse together to form one main pancreatic duct; this occurs in more than 90% of embryos. In approximately 10% of embryos the ventral and dorsal ducts fail to fuse together, resulting in pancreas divisum. In utero, the majority of the pancreas is drained by the dorsal duct which opens up into the minor papilla. The ventral duct drains the minority of the pancreas and opens into the major papilla. In adults however, this situation is reversed whereby 70% of the pancreas is drained by the ventral duct. Therefore in pancreas divisum, where fusion of the ducts does not occur, the major drainage of the pancreas is done by the dorsal duct which opens up into the minor papilla.

This is the embryologic progression of the pancreas formation. The 4^th picture is a normal pancreas. The duct of santorini or minor papilla was closed and the dorsal pancreas drains into the ventral duct. In pancreas divisum, the last step (4^th picture) does not happen. The pancreas formation is halted at the 3rd picture.