424 



ARTERIES. 



the superior mesenteric vein, and is surrounded by the superior mesenteric plexus 

 of nerves. Its branches are the 



Inferior pancreatico-duodenal. Ileo-colic. 



Yasa intestini tenuis. . Colica dextra. 



Colica media. 



The inferior pancreatico-duodenal is given off from the superior mesenteric 

 below the pancreas, and is distributed to the head of the pancreas, and the trans- 

 verse and descending portions of the duodenum ; anastomosing with the pancrea- 

 tico-duodenal artery. 



Fig. 225. The Superior Mesenteric Artery and its Branches. 



The vasa intestini tenuis arise from the convex side of the superior mesenteric 

 artery. They are usually from twelve to fifteen in number, and are distributed to 

 the jejunum and ileum. They run parallel with one another between the layers of 

 the mesentery ; each vessel dividing into two branches, which unite with a similar 

 branch on each side, forming a series of arches, the convexities of which are 

 directed towards the intestine. From this first set of arches branches arise, which 

 again unite with similar branches from either side, and thus a second series of 

 arches is formed ; and from -these latter, a third, and even a fourth or fifth series 

 of arches is constituted, diminishing in size the nearer they approach the intes- 

 tine. From the terminal arches numerous small straight vessels arise which 

 encircle the intestine, upon which they are minutely distributed, ramifying between 

 its coats. 



