THE PANCREAS. 



1737 



surface it sends a series of branches into the upper part of the body and tail. The 

 hepatic runs along the top of the front of the head and neck, doing the same. In the 

 groove between head and neck the gastro- duodenal sends the superior pancreatico- 

 duodenal across the front of the gland, supplying chiefly the head. The superior 

 mesenteric artery, just after its origin, sends from its right the inferior pancreatico- 

 duodenal. This vessel gives off a larger branch running to the right to meet the 

 superior pancreatico-duodenal on the front of the head, and sends a smaller branch 

 to the left along the lower surface. Sometimes the two branches which meet across 

 the head enclose it by a similar anastomosis behind. The veins follow in the main 

 the arteries. They are all tributaries of the portal system, and some open directly 

 into the portal vein. The lymphatics are many. Most of them run to the cceliac 

 and splenic plexuses. A small group of lymph-nodes is situated on the front of the 

 head. 



The nerves, composed chiefly of non-medullated fibres, are from the solar 

 plexus, by way of the cceliac, splenic, and superior mesenteric plexuses. 



FIG. 1465. 





Section of injected pancreas, showing intralobular capillary net-works; also convolutions of islands of 



Langerhans. X 50. 



Development. The human pancreas develops from two separate anlages, a 

 dorsal and a ventral one. The former, which appears by the fourth fcetal week, is 

 a direct outgrowth from the primitive duodenum. The ventral anlage, slightly later 

 in its formation, develops as two outgrowths, one from each side of the early bile- 

 duct, and is therefore not strictly a direct derivative from the gut. The left ventral 

 outgrowth soon disappears, leaving the right one connected with the bile-canal. 

 This close association is retained throughout life, as evidenced by the intimate rela- 

 tions between the common bile and pancreatic ducts. The dorsal pancreas rapidly 

 grows, elongates, and soon becomes the chief part of the organ, opening by an in- 

 dependent canal the duct of Santorini into the duodenum. The repeated division 

 of the duct and the proliferation and extension of the terminal compartments pro- 

 duce the system of excretory passages and glandular tissue of the organ. The ven- 

 tral pancreas, which has meanwhile increased more slowly, and in consequence of the 

 changes in the gut has suffered displacement to the left and behind, grows towards 

 the dorsal gland, with which it soon inseparably fuses. The head of the fully formed 



