118 TOPOGRAPHICAL ANATOMY OF THE 



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

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

 and stomach on the one hand, and the dorsal sac of the cjecum 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 the 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 po'iial ring (annulus 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 mammals ati'ord interesting illustrations of the possible 

 persistence or uisappearance 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. 



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