616 THE ARTERIES. 



3. Anterior or Great Mesenteric Artery (Figs. 365, 366). 



The anterior mesenteric artenj, which almost entirely supplies the mass of 

 intestines with blood, is as remarkable for its volume as for its complicated dis- 

 tribution. This complexity, together with that of the intestine itself, gives rise 

 to some difficulty in the study of this vessel ; but this may be averted by adopting 

 the mode of description — as simple as it is methodical — resorted to in his lectures 

 by Lecoq. 



The anterior mesenteric arises at a right angle from the posterior aorta, at 

 the renal arteries, and at 2 or 2^ inches behind the coehac axis, from which it is 

 separated by the pancreas ; it is directed immediately downwards, enlaced by the 

 anastomosing nerves of the solar plexus, and divides, after a course of from 1 to 

 1^^ inches, into three fasciculi of branches, which are distinguished as left, right, 

 and anterior. The left fasciculus goes to the small intestine ; the right is dis- 

 tributed to the terminal portion of that intestine, the cascum, and the first portion 

 of the flexure formed by the large colon ; the anterior is carried to the second 

 portion of that flexure, and to the origin of the small colon. The order in which 

 these three fasciculi have been indicated will also be that followed in their descrip- 

 tion ; this has, as will be observed, the advantage of recalling to the memory the 

 regular succession of the various parts of the intestine, and consequently the 

 passage of the food in this hnportant portion of the digestive canal. 



A. Arteries of the Left Fasciculus (Fig. 366, 2). — These arteries 

 number from fifteen to twenty, and are named the arteries of the small 

 intestine {vasa intestini tenuis), because of their destination. All spring at 

 once from the anterior mesenteric artery, either separately, or several in common, 

 and pass between the two layers of the mesentery to gain the intestine. Before 

 reaching the small curvature of that viscus, each divides into two branches, which 

 go to meet corresponding branches from the neighbouring arteries, and to anasto- 

 mose with them by inosculation ; from this arrangement results a series of 

 uninterrupted arterial arches, the convexity of which is downwards, and which 

 exist for the whole length of the intestine, opposite, and in proximity to, its 

 concavity. From the convexity of these arches emanate a multitude of branches 

 that arrive at the inner curvature of the intestine, and the divisions of which pass 

 to each of the faces of that viscus, to rejoin and anastomose on its great cm'vature. 

 These divisions are situated beneath the peritoneum or in the muscular tunic, 

 and send the majority of their ramuscules to the mucous tunic, which is there- 

 fore distinguished by its great vascularity — a feature common to all the hollow 

 organs in the abdominal cavity. 



Such is the general arrangement of the arteries of the small intestine ; and it 

 remains to indicate some of their special characters. These are as follows : 1. 

 The longest arteries of the small intestine are the most posterior, as they follow 

 the development of the mesentery, by which they are sustained. 2. The anterior 

 arteries generally form two series of superposed arches, before sending their 

 divisions to the intestine. 3. The first reaches the duodenum and anastomoses 

 with the duodenal artery — a branch given off by the coeliac axis. 4. The last 

 communicates with the ileo-csecal artery — one of the branches of the right 

 fasciculus. 



' This trunk of the anterior mesenteric is usually, in old horses killed for dissection, the 

 Beat of a more or less voluminous aneurism, wliicli sometimes extends to the artery placed at 

 tlie origin of the branches of the riglit fasciculus, and it is not unfrequently met with in one 

 or the other section of the anterior mesenteric artery. 



