and their Relation to the Peritoneum. 



487 



the transverse mesocolon would consist of only two layers, which 

 would embrace the gut and its artery. The paper which has been 

 mentioned was written, and specimens were shown, to demonstrate 

 that this was what took place. If this evidence is true, the usual 

 accounts of the relations of the transverse mesocolon and its contents 

 require to be modified. 



It may be remembered that a little while ago it was said that it 

 would be convenient to defer the final stages of the development of 

 the pancreas. When this organ was last spoken of it lay between the 

 folds of the mesogastrium just before this membrane was attached to 

 the spine (Diagram 5) . In consequence, the fossa between the meso- 



Diagram 8. 



The letters as before. To show the last stage in the disappearance of the fossa 

 between the omentum and transverse mesocolon. 



gastrium and the mesentery of the transverse colon intervened between 

 it and the spine. It is clear that if the highest part of the peritoneal 

 loop which forms this fossa was withdrawn, the pancreas would 

 naturally apply itself to the spine (Diagrams 6 and 7). That this is 

 what occurs need not be repeated, and as the under surface of the 

 mesogastrium is continuous with the left surface of the mesoduodenum, 

 the drawing out of the one causes the disappearance of the other. 



All the arteries of the alimentary canal from the stomach to the 

 rectum have now been discussed, and I have maintained that — 



First. All of them, even the splenic and hepatic, were originally 

 derived from the dorsal aorta for the supply of the 

 mid-gut. 



Second. That they reach their destinations by passing through the 

 mesentery. 



