596 



THE BLOOD-VASCULAR SYSTEM 



(4) The splenic or terminal branches, five to eight or more in number, are given off from the 

 splenic as it lies in the heno-renal hgament, and, entering the spleen at the hilum, are distributed 

 in the way mentioned in the description of that organ. 



THE SUPERIOR MESENTERIC ARTERY 



The superior mesenteric artery [a. mesenterica superior] is given off from the 

 front of the aorta a little below the coeliac, which it nearly equals in size; some- 

 times it forms a common trunk with the coeliac. Lying at first behind the pan- 

 creas and splenic vein, it soon passes forward between the lower border of that 

 gland and the upper border of the inferior portion of the duodenum, and, crossing 

 in front of the duodenum, enters the mesenterj^, in which it runs from left to' right, 

 in the form of a curve with its convexity to the left, to the caecum, where it 

 anastomoses with its ileo-colic branch. Its vein lies to its right side above, having 



Fig. 482.— The Superior Mesenteric Artery and Vein. 

 (The colon is turned up, and the small intestines are drawn over to the left side.) 



Left colic artery 

 Superior mes- 

 enteric artery 

 and vein 



Jejunum 



Middle colic 

 artery 

 Inferior pancre- 

 atico-duodenal 

 artery 



Right colic 

 artery 



Ileo-colic artery - 



Small 

 intestines 



previously crossed obliquely in front of the artery from left to right. It is sur- 

 rounded by the mesenteric plexus of nerves. The accessory portion of the head 

 of the pancreas dips in behind the vessel. 



The branches of the superior mesenteric are, in their primitive order: — 

 (1) the inferior pancreatico-duodenal; (2) the intestinal arteries; (3) the ileo- 

 colic; (4) the right colic; and (5) the middle colic. 



(1) The inferior pancreatico-duodenal [a. pancreatico duodenalis inferior] arises either from 

 the superior mesenteric as that ve.s.sel emerges from the contiguous margins of the pancreas 

 and inferior part of the duodenum or from its first intestinal branch. Crossing behind the 

 superior mesenteric vein, it courses upward and to the right between the head of the pancreas 

 and the duodenum, and beneath the ascending layer of the transverse meso-colon, to anas- 

 tomose with tlie superior pancreatico-duodenal. 



(2) The intestinal artnries [aa. intcstinales] arise from the convex side of the superior 

 mesenteric, and, varying from twelve to sixteen in number, radiate in the mesentery, where 



