118 TOPOGRAPHICAL ANATOMY OF THE 



basal part of the spleeu, the left kidney and the terminal part of the 

 great colon. In general terras, the pancreas is placed between the liver 

 and stomach on the one hand, and the dorsal sac of the csecum and 

 right dorsal colon on the other. 



The dorsal surface is largely covered by peritoneum, and is in con- 

 tact with a considerable area of the right kidney, the caudal vena cava, 

 the portal vein, the saccus ciecus of tlie stomach, the gastro-phrenic 

 ligament and the right lateral lobe and caudate process of the liver. 

 The ventral surface has only a limited peritoneal covering, which is 

 absent over the area that is adherent to the caecum and colon. 



Piercing the pancreas from its ventral to its dorsal surface is a short 

 passage, the jjortal ring (aunulus portarum), for the portal vein. 



The pancreas has two ducts, the larger of which, the pancreatic 

 duct (ductus pancreaticus), leaves the head of the gland, and immedi- 

 ately pierces the wall of the duodenum. When the time arrives to 

 examine the interior of the duodenum, it will be found that the pan- 

 creatic and bile ducts open into a common diverticulum. The 

 accessory pancreatic duct (ductus pancreaticus accessorius) also leaves 

 the head of the gland to pierce the wall of the duodenum immediately. 

 At a later stage in the dissection its opening will be found opposite to 

 that of the main duct. Both ducts are of considerable size and thin- 

 walled, and they intercommunicate within the substance of the 

 gland. 



The presence of two pancreatic ducts, and the termination of one of 

 them in common with the bile duct, can be accounted for by the mode 

 of development of the gland. The pancreas develops from dorsal and 

 ventral rudiments. The dorsal pancreas springs from the duodenum 

 opposite the bile duct ; while the ventral pancreas begins as two lateral 

 diverticula from the duodenal end of the bile duct. Some authorities 

 are of opinion that both ventral diverticula give origin to pancreatic 

 gland tissue, but others hold that only the right persists. In the horse, 

 the dorsal and ventral pancreas both retain their connection with the 

 gut ; and, consequently, in the adult there are two ducts opening into 

 the duodenum opposite each other, the ventral duct maintaining its 

 association with the bile duct.^ 



The double origin of the pancreas can also be adduced in explana- 

 tion of the occurrence of a portal ring, which is formed by the originally 



1 The various domestic niamnials afford interestin<^ illustrations of the possible 

 persistence or disappearance of the dorsal and ventral pancreatic ducts. In the 

 horse (as stated above) and in the dog both ducts persist ; in the ox and pig the 

 dorsal duct (opening into the duodenum independently) persists and the ventral 

 duct disappears ; and in the sheep the dorsal duct disappears and the ventral duct 

 (opening into the duodenum along with the bile duct) persists. 



