THE ABDOMEN 



813 



The ventral and dorsal parts of the pcincreas join, and the dorsal diverti- 

 culum (duct of Santorini) and ventral diverticulum now communicate by 

 freeh- anastomosing branches. Thereafter the duodenal portion of the duct 

 of Santorini usually atrophies and disappears. It may, however, persist, and 

 open, as an independent duct, into the second part of the duodenum. The 

 duct of Wirsung is persistent, and constitutes the principed duct of the fully 

 developed pancreas. From its mode of development it necessarily opens into 

 the common bile-duct. 



The islands of Langerhans, which are characteristic of the pancreas, are 

 formed of cells derived from the walls of the original epithelial tubes. These 

 cells become differentiated, and by their multipUcation. they give rise to 

 isolated cell-groups, l>Tng in the mesodermic connective tissue between the 

 lobules of the gland, where they are soon permeated by bloodvessels. 



Pylorus 



Duct of Santorini 



Common Bile-duct^ 

 Orifice of 

 Common Bile-duct 

 and Pancreatic Duct. 



Duct of Wirsung 



Dorsal Pancreas 



- - Duodeno-jejunal Flejrare 



--•■ Superior Mesenteric Vessds 



Ventral Pancreas 



Fig. 350. — The Pancreas in Early Life. 



The development of the pancreas, as stated, proceeds within the meso- 

 gastrium. It occupies a mesial position at this stage, and is completely 

 invested by the mesogastrium. When, however, the stomach and duodenum 

 undergo partial rotation towards the right, the pancreas also turns on its 

 right side. The head of the gland incUnes towards the right, and occupies the 

 U-shaped curve described by the duodenum. The body and tail pass to the 

 left, the body coming to lie in front of the left kidney, and the tail appljong 

 itself to the spleen. The entire gland, therefore, now Ues across the dorsal 

 body-wall. 



The dorsal layer of the mesogastrium. covering the dorsal surface of the 

 pancreas, becomes absorbed, and consequently the pancreas of adult Ufe is 

 situated behind the peritoneum, and is therefore spoken of as being retro- 

 peritoneal. 



Structure of the Spleen. 



The spleen is the largest ductless gland in the body. It has 

 two coats, serous and fibrous, inseparably connected together. 

 The serous coat is formed by the peritoneum. The fibrous coat 

 or tunica -propria is composed of fibrous tissue, with a con- 

 siderable admixture of elastic tissue, and a certain amount of 



