and their Relation to the Peritoneum, 



483 



are the same, the outgrowth determines its division into small intestine 

 and colon. 



The developmental changes which afterwards occur in the upper 

 part are so slight that they do not seem to demand further comment. 

 An exception may be made in the case of the duodenum, for owing to 

 the presence of the pancreas, the arteries in its neighbourhood are 

 more complicated. 



As far as the duodenum itself is concerned, it has been explained 

 why the hepatic artery should send branches to it ; the rationale of 

 its supply from the superior mesenteric is so obvious that it does not 

 seem to require notice. It would be hard to explain why parts of the 

 duodenum cease to have a mesentery, but the fact of the disappearance 

 of this serous fold can have no influence upon the sources of its blood 

 supply ; that was determined long before the mesentery became 

 obliterated. 



With regard to the arteries of the pancreas, one or two points 

 await solution. At first it may not be evident why it should be sup- 

 plied by the vessels of the duodenum and spleen. It is well recognised 

 that the pancreas commences as a caecal prolongation from the duo- 

 denum. In a human embryo about inches long the elongated 

 mesogastrium, i.e., great omentum, has not yet involved the transverse 

 colon; and when this membrane is lifted upwards, it may be seen 

 continuous with the mesoduodenum. The pancreas, already of con- 

 siderable size, stretches from the duodenum into the mesoduodenum, 

 and onwards into the mesogastrium,* where it applies itself to the 

 spleen, previously described as being between the layers of this mem- 

 brane. The splenic artery may be seen as a delicate streak in the 

 mesogastrium close to the pancreas, and is at this time one of its most 

 available sources of blood supply. It is evident that the fact of this 

 organ being at one time between the layers of the mesentery explains 

 why it should be supplied by its vessels, such as the splenic and 

 duodenal; it also explains why, as Haller (quoted by Cruveilhier, 

 vol. iii, p. 68) points out, the pancreas may have a large artery 

 (pancreatica suprema) arising from the cseliac axis, superior mesenteric, 

 or aorta. It will be remembered that the original vessels of the 

 mesentery are numerous, and that even the liver sometimes appro- 

 priated more than one; evidently the same is the case with the 

 pancreas. In conclusion, as regards the position of the pancreas 

 between the layers of the mesentery, it is permanent in some animals, 

 e.g., the hedgehog (see also sp. 780a and 781a, R. C. S. Museum). 

 The ultimate relations of this organ to the serous membrane may be 

 conveniently discussed a little further on. 



* July 6th, 1885. — This is exactly the anatomical relation which has been de- 

 scribed by Professor Anderson as existing in the seal (" Journal of Anatomy and 

 Physiology," xix, p. 228). 



VOL. XXXVIII. 2 M 



