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to the left portion of tlio colic iVxuiv, which it passes over, IK-IK nth tin- 

 peritoneum, from the terminal extremity of the viscus to the pelvic curv;itinv, 

 where it meets tho right artery; in this manner it follows a conrsr tli<- 

 inverse of that pursued by the aliment, and whence its name of retroijrmlr 

 colic artery. 



Considered collectively, the two colic arteries represent a loop or flexure 

 exactly like that formed by tho large colon itself. They proceed parallel to 

 each other, and finish, after being slightly separated, by uniting to form a 

 parabolic curve. This arterial loop occupies a deep position on tho 

 intestinal loop, being found on the inferior face of the first and fourth 

 sections of the large colon, in tho concavity of the flexure which gives 

 rise to the suprasterual and diaphragmatic curvatures, and on the superior 

 plane of the second and third portions of the viscus. 



A considerable number of collateral branches escape perpendicularly 

 from this arterial loop, and pass into the membranes of the intestine ; 

 some of them establish a transverse communication between tho two vessels. 



FIRST ARTERY OP THE SMALL COLON (Figs. 271, 9 ; 272, 4). This 

 branch, whoso calibre is often considerable, is inflected to the left, 

 downwards and backwards, to be placed in the substance of the colic 

 mesentery, very near the lesser curvature of the floating or small colon. It 

 soon meets a branch of the small mesenteric artery, with which it anasto- 

 moses by inosculation. 



D. INNOMINATE BRANCHES OP THE GREAT MESENTERY. These are the 

 twigs sent to the lymphatic glands, supra-renal capsules, mesentery, and 

 pancreas, and whoso existence it is sufficient merely to mention. Among 

 those supplied to the pancreas, there is one of somewhat considerable volume. 



E. THE ANASTOMOSES OP THE GREAT MESENTERIC ARTERY. The 

 multiplicity and calibre of these anastomoses assure, in the most favourable 

 manner, the circulation of the blood in the intestinal mass, which, by reason 

 of its great mobility, is exposed to displacements capable of inducing more or 

 less extensive compression. Not only do these anastomoses unite the 

 different branches destined to the same portion of the viscera, be it the small 

 intestine, the caecum, or the large colon ; but they also establish communica- 

 tions between the great mesenteric artery and tho neighbouring trunks, 

 which in case of need can maintain the circulation : as, for example, when the 

 two intestinal arteries are completely obstructed. The blood from the 

 coeliac trunk can really pass from tho duodenal artery into tho branches 

 of the left fasciculus of the great mesenteric artery : then by the ilco-ctecal 

 artery into the branches of the right fasciculus, and thence into the k-ft 

 colic artery, which, finally, transmits it to tho first artery of tho small colon, 

 as well as to the arches of the small mesenteric artery. Tho communica- 

 tion existing between the broncho-oesophageal and the cosliac trunks, through 

 tho medium of the cesophageal and gastric arteries, even allows a collateral 

 circulation to be formed, and which would be capable of supplementing the 

 posterior aorta, supposing that vessel tied behind the trunk that distributes 

 blood to the bronchi and oesophagus. 



4. Small Mesenteric Artery. (Fig. 272.) 



This artery carries blood to tho small colon and rectum, and arises at a 

 right angle from the inferior face of the abdominal artery, from 4 to 

 6 inches behind the great mesenteric. It descends between the two layers 

 of the colic mesentery, and is soon inflected back in describing a curve 



