THE PANCREAS 



1195 



receiving branches all along, which enter nearly at right angles. It is largest in 

 the head of the pancreas (diameter about 3 mm.) where it turns obliquely down- 

 ward. As it approaches the duodenum, it is joined by the common bile duct, the 

 two running side by side. They pass obliquely through the wall of the duodenum 

 for a distance of about 15 mm. (usually causing a fold of the mucosa, the plica 

 longitudinalis duodeni). They terminate finally, usually by a common aperture, 

 but sometimes separately, on the duodenal papilla major, as described in connec- 

 tion with the interior of the duodenum. The common aperture is somewhat nar- 

 row, but just preceding this the duct is frequently dilated, forming what is called 

 the ampulla of Vater. 



The accessory pancreatic duct (duct of Santorini) is nearly always present 

 (figs. 922, 957), but variable. This duct is small, and lies within the head of the 

 pancreas. At its left end, it usually joins the main duct in the neck of the pan- 

 creas. From here it extends nearly horizontally across to the upper part of the 

 descending duodenum and, piercing its wall, usually ends upon the small papilla 

 minor, about 2 cm. above and slightly ventral to the papilla major. The relations 

 of the ducts are explained later under development. 



Fig. 957. — The Pancreas and its Ducts, Dissected from Behind. 



Duct of pancreas Accessory duct of Santorini Common bile-duct 



Blood-vessels. — The pancreas receives blood chiefly from the splenic artery through its 

 pancreatic branches, and from the superior mesenteric and hepatic by the inferior and superior 

 pancreatico-duodenal arteries, which form a loop running around, below, and to the right of 

 its head. 



The blood is returned into the portal vein by means of the splenic and superior mesenteric 

 veins. 



Lymphatics. — The lymphatics terminate in numerous glands which lie near the root of the 

 superior mesenteric artery, above and below the neck of the pancreas. AU the lymphatics 

 drain ultimately into the coeliac glands. 



Nerves. — These are branches of the coeliac plexus which accompany the arteries entering 

 the gland. The main part of the coeliac plexus lies behind the gland. 



Minute anatomy. — In many respects, the pancreas resembles the salivary glands in struc- 

 ture, hence its German name 'Bauchspeicheldrtise' ('abdominal salivary gland'). The 

 gland proper is racemose (or tubulo-racemose) in structure, the secreting cells characteristically 

 granular and 'serous' in type. The thin-walled 'intercalary ducts,' often invaginated to 

 form 'centroacinar' cells, are characteristic. The lobules are very loosely joined by areolar 

 tissue, and there is no distinct fibrous capsule around the gland. The most important of the 

 distinctive characters of the pancreas is the presence throughout the gland of numerous small 

 interlobular cell-masses of varied form and size — the islets of Langerhans (fig. 959). These have 

 no ducts, but are richly supplied with blood-vessels. They are ductless glands of great import- 

 ance in sugar metabolism, and their removal or disease produces diabetes. While derived 

 embryologically from the same entodermal anlage which gives rise to the pancreas gland 

 proper, they apparently have no direct connections with it in the adult. The question as to 

 the possible metamorphosis of acini into islets, or vice versa, under certain conditions (e. g., 

 hunger) in the adult has been much disputed. Bensley, however, has recently presented strong 

 evidence against this view. 



Development of the pancreas. — The pancreas has its origin in three entodermal buds, one 

 of which (the dorsal anlage) grows from the dorsal portion of the duodenum, the other two 

 (ventral anlages) from either side of the bile-duct. Of the two latter, only that growing from 

 the right side of the bile-duct needs further consideration, as the other soon disappears. The 

 dorsal anlage grows at first more rapidly than the ventral, which arises from the bile-duct. In 

 their further growth both the dorsal and ventral anlages become lobed, these lobes dividing 

 further to form the ducts and the alveoh of the gland. By about the end of the second month 

 the distal end of the ventral portion comes in contact with the dorsal portion at a short distance 



