DEVELOPMENT OF THE LIVEE AND PANCKEAS. 



1255 



hepatic vein, and the capillary network 



constitute the bile-ducts within the liver. Adjacent trabeculse become arranged into the 

 form of a lobule, each with a vascular channel in its interior, which communicates with 

 the vascular network in the surface of the lobule by capillary intervals between adjacent 

 trabeculse. 



The central vein becomes a tributary of 

 becomes the terminal 

 distribution of branches 

 of the portal vein. 



The proximal portion gtomach 



Spleer _ ^ 



/ iaphragm 

 --Spleen 

 Line crosses 

 mesogastrium 



-Pancreas 



Superior mesen- 



Small intestine^ VWV (^^^^ teric artery 



Superior mesen- 



CEsophagus 



Ventral mesentery 

 Liver 



Ventral mesentery 

 Bile-duct 

 Stomach 



Duodenum 



teric artery 



Small 

 intestine 



Vitelline 

 duct 



Caecum 



Inferior mesenteric artery 



Rectum 



i -Colon 



Inferior mesen- 

 teric artery 



Rectum 



The mesentery 



Aorta 



FIG. 977. Two DIAGRAMS TO ILLUSTRATE THE DEVELOPMENT OF THE 

 INTESTINAL CANAL. 



The figure to the right shows the rotation of the intestinal loop around the 

 superior mesenteric artery. In both figures the parts are supposed to be 

 viewed from the left side. 



of the original hollow 

 diverticulum becomes 

 the bile-duct, and the 

 gall-bladder and cystic 

 duct are formed by an 

 evagination from it. 



As the liver increases 

 in size, it begins to pro- 

 ject down from the in- 

 ferior part of the septum 

 transversum into the 

 ventral mesentery, so 

 that now, instead of 

 being situated within the 

 septum, it looks like an 

 appendage of its inferior 

 surface. In other words, 

 the septum begins to 

 differentiate into two 

 parts an inferior, the 

 liver, and a superior, 

 which constitutes the 



greater portion of the diaphragm, both of these having been at first one continuous mass. 

 In the course of development the separation of the two becomes more marked, and finally 

 is complete everywhere except at the coronary and lateral ligaments behind, and at the 

 falciform ligament in front, where they are still connected. 



As the liver separates off from the future diaphragm, and descends into the abdomen, 



I lies between the layers of the ventral mesentery a fold which connects the stomach 

 and duodenum with the anterior abdominal wall. 

 f\ This is divided by the liver into two parts a 



\^%M\ lower, stretching from the front (lesser curvature) 



\ ija of the stomach to the liver, which becomes the 



\ *.-M-stomach lesser omentum ; and an upper, stretching from 

 the liver to the diaphragm and anterior wall of 

 / jjj the abdomen, which forms the falciform ligament. 



ft / ' *^r 2. Pancreas. The pancreas is developed at 



Hepatic ducts ^^\ '(ji a veI 7 ear ly period in man (being present in 



Gall-bladder < NJ\ \ k^^^^ embryos of 5 mm.) from two outgrowths from 



"* *iu^sJ ^^h s rowth the alimentary canal, a dorsal and a ventral. 

 Pancreas ^^N ^ "^^ The dorsal rudiment is an outgrowth from 



ventral growth '~^~'"&/ i "-Duodenum ^ e d orS al aspect of the intestine, anterior to the 



origin of the hepatic outgrowth. The ventral 

 rudiment grows at a later stage from the root 



^^"\ I of the hepatic bud in the form of two ventral 



offshoots, one on either side. That on the left 

 FIG. 978,-DiAGRAM OP THE ORIGIN OF THE side however, soon disappears. 



LIVER AND PANCREAS. Through the rotation of the duodenum around 



its long axis, the dorsal and ventral rudiments 



approach one another and become fused, and their ducts open on the left side of the 

 duodenum. The connecting stalk between the ventral rudiment and the hepatic bud 

 becomes the main duct of the pancreas, while the connexion of the dorsal outgrowth 

 with the duodenum remains as the accessory pancreatic duct. In embryos of the fifth 

 week, a large dorsal pancreatic rudiment is present, and also a smaller ventral rudiment, 

 ich opens into the duodenum in common with the bile-duct, and lies on the right of 





