In other cases, also without pathological conditions, the proximal duct is the larger of the two and serves as the principal channel of pancreatic secretion, the canal of Wirsung being small. This is evidently a persistence and further development of the early embryonic relative condition of the two outgrowths above described (Fig. 190). On the other hand the duct of Santorini may not open at all into the duodenum, terminating in small branches which drain the proximal part of the head of the gland (Fig. 191). Schirmer has examined the arrangement of the pancreatic ducts in 105 specimens. In 56 of these the duct of Santorini passed from the main duct into the duodenum, opening upon a papilla situated 2.5 cm. above the common opening of the bile duct and canal of Wirsung. In 19 the duct of Santorini was well developed but did not open into the duodenum. In but 4 cases the duct of Santorini formed the only pancreatic duct, the lower opening being occupied by the bile duct alone (Fig. 192). We may assume in these cases failure of development of the distal outgrowth connected with the primitive hepatic bud, leaving only the proximal duodenal outgrowth to form the entire adult gland. Figs. 188 and 189 show the normal arrangement of the duodenal openings of the biliary and pancreatic ducts. Figs. 190 to 192 show schematically the variations in the relative development and the adult arrangement of the pancreatic ducts. =Diverticulum and Papilla Vateri.=--From what has been said regarding the embryonic union of the distal pancreatic outgrowth with the hepatic bud it will be easy to recognize the corresponding features in the arrangement of the adult duodenal termination of the common bile-duct and canal of Wirsung. The dilated interior of the duodenal papilla (diverticulum Vateri) corresponds to the embryonic segment between the intestinal opening of the primitive liver duct and the point when this duct gives off the distal larger pancreatic outbud (Figs. 186, 187, 188, 193 and 194). [Illustration: FIG. 194.--Adult human subject. Mucous membrane of pyloro-duodenal junction and of duodenum. (Columbia University Museum, No. 1840.)] The union of the pancreatic and biliary ducts to form the recess of the diverticulum Vateri, which then opens by a single common orifice into the duodenum, is better marked in some of the lower vertebrates than in man. [Illustration: FIG. 195.--Duodenum, with entrance of pancreatic and biliary ducts and well-developed diverticulum Vateri in the cassowary, _Casuarius casuarius_. (Columbia University Museum, No. 1821.)] Fig. 195 shows the proximal portion of the duodenum of the cassowary (_Casuarius casuarius_) with the biliary and pancreatic ducts and the diverticulum at their confluence in section.