STOMACH AND INTESTINE. 



379 



to allow of the much quicker destruction of 

 their poisonous properties by a more or less 

 perfect oxidation. 



Arteries of the intestines. We have seen 

 that the stomach and duodenum are supplied 

 with arterial blood by means of various twigs 

 derived from the three branches of the ccehac 

 axis, which springs from the upper part of 

 the abdominal aorta. The remainder of the 

 intestinal canal is furnished witli arteries which 

 are given oft' by two large branches of the 

 abdominal aorta. These branches are named, 

 from their position and distribution, the 

 superior and the inferior mesenteric. 



The superior mesenteric artery (a, fig. 277.), 

 the longer of these two branches, is distributed 

 over that large segment of the intestine which 

 is formed by the lower part of the duodenum, 

 the whole of the jejunum, ileum, and ccecum, 

 and the first two-thirds of the colon. The 



Fig. 217. 



Distribution of tke superior mesenteric artery to the 

 small and large intestine. 



a, trunk of the superior mesenteric artery ; b, ilco- 

 colic artery ; c, its iliac branch ; d, its colic branch ; 

 e, right colic artery, /, middle colic artery; g, 

 arches formed by the anastomosis of the branches 

 to the small intestine ; p, pancreas ; du, duodenum ; 

 j, jejunum; i, ileum ; c a, caecum ; a c, ascending 

 colon ; t c, transverse colon ; d c, descending colon. 



trunk of the vessel comes off from the aorta, 

 at a point which about corresponds to the 

 upper border of the second lumbar vertebra. 

 It is separated from the cceliac axis by the 

 pancreas ; and hence is distant about a third 

 of an inch from the origin of the latter vessel. 

 From this commencement, it passes down- 

 wards and forwards, crossing over the termi- 

 nation of the duodenum, so as to reach the 

 upper part of the mesentery. It now con- 

 tinues downwards between the two layers of 

 this fold of peritoneum, which it occupies near 



its attachment to the posterior wall of the 

 abdomen. Hence its length and direction 

 correspond to those of the attached border of 

 the mesentery itself ; and are such, as to 

 conduct it downwards and obliquely towards 

 the left side, to a termination that corresponds 

 to the end of the ileum, or the commencement 

 of the coecum. But the branches given off to 

 these latter segments of the intestine by the 

 trunk of the vessel are so large, and so directly 

 continuous with its previous course, that it is 

 only in a very arbitrary and limited sense that 

 we can speak of it as ending in this situation. 

 The arrangement of the larger or primary 

 branches of the superior mesenteric artery- 

 is liable to great variation, but is generally as 

 follows. 



The trunk of the superior mesenteric artery 

 is directly continuous with a large vessel (I), 

 fig. 277.), which, when it has reached a dis- 

 tance of about two inches from the ccecum, 

 divides into two others ; of these the upper 

 (d,fig. 27'7.)passes towards the ccecum, and the 

 lower (c,fig. "277.) towards the ileum. Thez'fco- 

 cofic artery (b, fig. 277.), as the common trunk 

 is named prior to its bifurcation, usually gives 

 off from its right side oneof rather smaller size, 

 about three inches from the border of the bowel. 

 The latter, which is called the artcria colica 

 dextra, or right colic artery (e,ftg. 277.), often 

 arises by a separate trunk from the superior 

 mesenteric. It takes a course almost horizon- 

 tally outwards, or towards the right side, 

 lying underneath the single layer of perito- 

 neum which covers in the ascending colon, so 

 as to reach this part of the large intestine at or 

 near the middle of its height. Finally, at a dis- 

 tance of little more than an inch from its 

 entering the mesentery, the trunk of the supe- 

 rior mesenteric artery gives oft' a large branch, 

 the arteria colica media (f,fig. 277.), which 

 passes upwards and back wards, enters between 

 the two layers of the transverse meso-colon, 

 and is distributed to the transverse colon, 

 which it reaches at the middle of its posterior 

 border. Besides these named branches, the 

 superior mesenteric gives oft' numerous arte- 

 ries (at g, fig. 277.), of almost equal size, 

 which have not received any special designa- 

 tion. These twenty or thirty branches leave 

 the left side of the artery, at various points 

 between the lower border of the duodenum 

 and the origin of the ileo-colic artery ; and 

 pass outwards, or to the left side, towards 

 their distribution on the small intestine. 



The further course of all these branches 

 towards the small and large intestine affords 

 a remarkable ; instance of an arterial ana- 

 stomosis ; such as is almost unparalleled in 

 the whole of the body for the freedom and 

 frequency of its communications, and the 

 size of the^vessels by which they are effected. 

 Each of the primary branches just alluded to 

 bifurcates : and its two resulting branches 

 unite with those above and below them, so 

 as to form a set (g,/g.277.) of arterial arches ; 

 from the convexity of which spring new 

 trunks, to divide and inosculate in a similar 

 manner. This arrangement, which prevails 



