396 Obstruction of the Mesenteric Arteries. 



grow into and obstruct the art. colica ventr., or one of the 

 art. coecales, or the ramus iliacus; if a thrombus in the art. ileo- 

 coecocolica grows centrally, it may spread into the art. colica 

 dors., or into one of the arteries of the jejunum. In such cases, 

 according to the observation of the authors, obstruction of the 

 branch occurs in the following manner: The blood current 

 moves the free floating end of the thrombus and eventually 

 presses it into the opening of one of the branches of the main 

 trunk. If the terminal free end has once been pressed into an 

 opening, then closure is intensified, because there is a decreased 

 blood pressure peripherally and an increased blood pressure 

 centrally. However, if a sufficient collateral circulation is estab- 

 lished, the blood pressure again may become evenly balanced in 

 front of and behind the obstruction, and the thrombotic plug 

 may again become free. 



In the larger mesenteric vessels thrombosis may bring 

 about embolic closure of smaller branches. Since such emboli 

 are, as a rule, small, and since they therefore obstruct only 

 smaller arteries, they do not, as a rule, produce any serious 

 disturbances of circulation, either alone or in connection ^\dth 

 the primary thrombus. Only if arranged in arteries one above 

 the other, like the floors of a building, might emboli become dan- 

 gerous. No doubt every thrombus does not necessarily lead to 

 embolus formation. On the other hand, thrombosis in other 

 organs or in the aorta, may lead to embolism in the mesenteric 

 arteries. 



The effect upon the circulation in the intestines of obstruc- 

 tion of the mesenteric arteries depends mainly upon the size 

 and the number of the obstructed vessels, upon the seat and the 

 degree of stenosis and upon the size of the anastomoses which 

 connect neighboring vessels with those that are thrombosed. 



The arteria mesenterica anterior sive cranialis (Fig. 40 h.) supplies all por- 

 tions of the intestines with blood, except the oral portion of the duodenum, which 

 is supplied by the art. ccEliaca, and the middle and caudal third of the small colon 

 (socalled abdominal portion) of the rectum, which get their blood from the art. 

 mesent. posterior, s. caudalis (n). The arteria mesent. ant. forms a short, strong 

 trunk, only a few centimeters long ; this gives off, in front and somewhat to the left, 

 the art. colica dorsalis (d), which supplies all upper branches of the colon, and the 

 art. col. media («), which supplies the cranial third of the small colon. The two 

 last named arteries usually arise from a common trunk (c) ; somewhat more backward 

 and to the left arise the 17-20 jejunales (i), which supply the small intestines. 

 In this manner the main trunk becomes thinner and is now known as the art. ileo- 

 ccecocolica (/) ; it is two to four cms. long; it first gives off the arter. colica ven- 

 tralis (g), which supi)lies the lower branches of the colon; the remaining portion, 

 the art. ileo-coecalis, divides into the art. coecalis (l), lateralis (A) and the ramus 

 iliacus (m) to supply the cecum and the ileum. The arter. cnpcalis lateralis gives otf 

 a branch to the lateral wall of the right lower branch of the colon (art. colica 

 lateralis of Franck). 



The most cranial artery of the small intestines (art. jejunalis) anastomoses 

 with the arter. pancreatico-duodenalis, that is, with the art. coeliaca in the region of 

 the duodenum, by a tolerably large arterial arch situated in the mesentery. The 

 different arteries of the small intestines communicate with the ramus iliacus by 

 similar archlike ana.stonioses (,?"). The art. colica ventralis and the ramus iliacus 

 are connected with the vessels of the cecum which among themselves possess rich 

 anastomoses. The art. colica dorsalis is continued immediately into the art. colica 

 ventralis at the pelvic flexure, and this forms the largest anastomosis of the animal 



