618 THE ARTERIES. 



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 con- 

 cavity of the flexure which gives rise to the supra-sternal 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 Artery of the Small or Floating Colon (Figs. 283, 9 ; 366, 4).— 

 This branch, the calibre of which is often considerable, is inflected to the left, 

 downwards and backwards, to be placed in the colic mesentery, very near the 

 lesser curvature of the floating or small colon. It soon meets a branch of the 

 posterior mesenteric artery, with which it anastomoses by inosculation. 



D. Innominate Branches of the Great Mesentery. — These are the 

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

 the existence of which 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 multi- 

 plicity 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 communications between the anterior 

 mesenteric artery and the neighbouring trunks, which in case of need can main- 

 tain the circulation — as, for example, when the two intestinal arteries are com- 

 pletely obstructed. The blood from the cceliac axis can really pass from the 

 duodenal artery into the branches of the left fasciculus of the anterior mesenteric ; 

 then by the ileo-caecal 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 mesenteric artery. The communi- 

 cation existing between the broncho-cesophageal and the cceliac trunks, through 

 the medium of the oesophageal and gastric arteries, even allows a collateral 

 circulation to be formed, 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. Posterior or Small Mesenteric Artery (Fig. 366). 



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

 angle from the inferior face of the posterior aorta, from 4^ to 6 inches behind 

 the anterior mesenteric. It descends between the two layers of the colic 

 mesentery, and is soon inflected back in describing a curve upwards, to pass 

 above the rectum ; when near the anus, its terminal divisions enter the walls 

 of that intestine. 



In its course this artery gives off, at pretty regular intervals, thirteen or 

 fourteen branches, the foremost of which are the largest and longest ; they 

 originate from the convexity of the artery — that is from below, and either singly 

 or in clusters ; the latter disposition is the most common for the first four or 

 five. They descend into the mesentery, and arrive near the superior curvature 



( 



