532 THE ARTERIES. 



to the left portion of the colic flexure, which it passes over, beneath the 

 peritoneum, from the terminal extremity of the viscusto the pelvic curvature, 

 where it meets the right artery ; in this manner it follows a course the 

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



colic (tVtGVll 



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

 exactly like that formed by the 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 the 

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

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

 rise to the suprasternal 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 the two vessels. 



First Aetery of the Small Colon (Figs. 271, 9 ; 272, 4). — This 

 branch, whose 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 of the Great Mesentery. — These are the 

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

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

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



E. The Anastomoses of 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 the 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 

 cceliac trunk can really pass from the duodenal artery into tlie branches 

 of the left fasciculus of the great mesenteric artery : then by the ileo-csecal 

 artery into the branches of the right fasciculus, and thence into the left 

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

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

 tion existing between the broncho-cesophageal and the coeliac trunks, through 

 the medium of the CBSophageal 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 the 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 



