8l2 A MANUAL OF ANATOMY 



epithelial cells, the neck being Uned by polyhedral cells. In the 

 larger ducts a connective- tissue coat is superadded to the basement 

 membrane, which is now covered by columnar epithelium. The 

 duct of Wirsung, though of comparatively large size, has a thin 

 wall destitute of muscular fibres, and composed of two coats — 

 external fibrous and internal mucous. The mucous coat is smooth 

 and covered by columnar epithelium. 



Varieties — (i) Small Pancreas. — This consists in a permanent detachment 

 of the unciform process, or that part of the pancreas which extends along the 

 tipper aspect of the third part of the duodenum and has the superior mesenteric 

 vessels in front of it. (2) The head of the pancreas may surround the second 

 part of the duodenum more or less completely. (3) Accessory Pancreas. 

 When an accessory pancreas is present it is usually met with in the wall of the 

 upper part of the duodenum, but it may be found in the wall of the stomach. 

 (4) The duct of Wirsung sometimes opens into the duodenum independently 

 of, but close to, the common bile-duct. 



Blood-supply. — The pancreas derives its arteries from (i) the 

 pancreatic branches of the splenic artery, one of which accom- 

 panies the principal duct from left to right, and is known as the 

 artetia pancreatic magna; (2) the superior pancreatico- duodenal of 

 the gastro-duodenal from the hepatic ; and (3) the inferior pancre- 

 atico- duodenal of the superior mesenteric. 



The veins are (i) the pancreatic veins, which open into the splenic 

 vein, and (2) the pancreatico-duodenal vein, which terminates in 

 the superior mesenteric vein. All the pancreatic venous blood 

 eventually passes into the portal vein. 



Lymphatics. — These commence as Ijonphatic clefts around the 

 alveoli, and pass chiefly to the cceliac glands. Some of them, how- 

 ever, terminate first in the superior mesenteric glands in contact 

 with the upper part of the superior mesenteric artery. 



Nerves. — ^These are derived from offshoots of the hepatic, splenic, 

 and superior mesenteric plexuses, and accompany the arteries. 

 They are chiefly composed of non-medullated fibres. 



Development or the Pancreas. — The tubular portion of the pancreas is of 

 entodermic origin, but its connective tissue and vascular elements are developed 

 from mesoderm. 



The pancreas is developed from two entodermic diverticula — dorsal and 

 ventral. The dorsal diverticulum is an evagination of the entoderm of the dorsal 

 wall of the duodenal portion of the primitive gut. The ventral diverticulum 

 springs from the primitive hepatic diverticulum close to the ventral wall of the 

 duodenum, which diverticulum subsequently forms the common bile-duct. 

 The dorsal diverticulum extends between the two layers of the mesogastrium, 

 where it comes into relation with the developing spleen. This diverticulum 

 gives off lateral epithelial tubes, which ramify freely, and so build up an acino- 

 tubular gland. The acini appear as enlargements of the walls of the terminal 

 tubes. By means of the ramifications of the dorsal diverticulum, the greater 

 part of the head, body, and tail of the adult pancreas are formed. 



The ventral diverticulum, which is small, gives rise to ramifying epithelial 

 tubes, like the dorsal diverticulum, and these form the lower part of the head 

 of the adult pancreas. The ventral diverticulum, an evagination, as stated, 

 from the future coinnion bile-duct, gives rise to the principal duct of the 

 pancreas, or duct of Wirsung, and the dorsal diverticulum forms the accessory 

 pancreatic duct, or duct of Santorini. which consequently opens directly into 

 the duodenum. 



