482 Mr. C. B. Lockwood. Arteries of the Abdomen 



a human embryo, an inch or an inch and a-half long, the stomach is 

 almost vertical. It has been remarked before that the space behind 

 it corresponds to the lesser cavity of the peritoneum. The communi- 

 cation between this and the greater sac lies between the right border 

 of the stomach and lesser omentum and the posterior wall of the 

 abdomen. Now at this early stage of development the liver is of 

 enormous size, and nearly fills the abdominal cavity, descending as 

 low as the pubes. In consequence its transverse fissure occupies an 

 exceedingly low position. Afterwards the relative size of the liver 

 diminishes, and it may be said to retreat beneath the ribs and costal 

 cartilages. It seems reasonable to argue tbat when the liver makes 

 this ascent it must needs take the lesser omentum, pylorus, and 

 hepatic artery up with it; and it would further follow that the 

 stomach would become more nearly horizontal, and the hepatic artery 

 acquire an upward direction. It is these events which cause the 

 Foramen of Winslow to assume its permanent appearance and posi- 

 tion. 



Three important arteries, the gastric, splenic, and hepatic, have 

 been passed in review. From the details of their development princi- 

 ples of wide applicability may be deduced. 



First. That they were originally derived from the dorsal aorta for 



the supply of the mid-gut. 

 Second. That they reach their destination by passing through the 



mesentery. 



Third. That they participate in all the changes the mesentery 

 undergoes. 



Fourth. That if an organ is developed in the mesentery or from 

 the gut, it obtains, part at least, of its vascular supply 

 from the vessels of the mesentery, or from those of the 

 gut from which it sprung. 



The attempt may now be made to apply these principles to the 

 remainder of the human alimentary canal. Before discussing in 

 detail the arteries of the intestines and their appendage, the pan- 

 creas, the development of these organs requires a passing notice. 

 The formation of the large and small intestines has been fully 

 described elsewhere {e.g., Balfour, Gegenbaur, Quain, &c). Reca- 

 pitulated as briefly as possible, it may be stated that in human 

 embryos an inch long the alimentary canal forms a loop extending 

 from the stomach to the pelvis. The convexity of this loop is 

 situated in the large aperture which afterwards becomes the um- 

 bilicus; its concavity is fastened to the spine by a considerable 

 mesentery. A small protrusion appears about the middle of the 

 intestine, and marks the commencement of the caecum and vermiform 

 appendix. As the calibre of the upper and lower parts of the bowel 



