379 STOMACH AND INTESTINE. 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 coeliac axis, which springs from the upper part of the abdominal aorta. The remainder of the intestinal canal is furnished with arteries which are given off 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 cæcum, and the first two-thirds of the colon. The Fig. 277. Distribution of tke superior mesenteric artery to the small and large intestine. a, trunk of the superior mesenteric artery ; b, ileo¬ colic artery ; c, its iliac branch ; d, its colic branch ; e, right colic artery ; f 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 œ, cæcum; ac, 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 coeliac 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 cæcum. 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 (b, fig. 277.), which, when it has reached a dis¬ tance of about two inches from the cæcum, divides into two others ; of these the upper (d,fig• 277.)passes towards the cæcum,and the lower {c,fig. 277.) towards the ileum. Theileo- colic artery (b,fig. 277.), as the common trunk is named prior to its bifurcation, usually gives off from its right side one of rather smaller size, about three inches from the border of the bowel. The latter, which is called the arteria colica dextra, or right colic artery (e,fig. 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 off a large branch, the arteria colica media ( ffig. 277.), which passesupwards and backwards,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 off 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 the1!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,fig. 277.) of arterial arches ; from the convexity of which spring new trunks, to divide and inosculate in a similar manner. This arrangement, which prevails