THE VASCULAR SYSTEM 207 



branches arise which are distributed to the distal end of the duo- 

 denum, while a few small vessels pass into the pancreas from the 

 main artery during its passage through the gland. The next impor- 

 tant division of the vessel occurs about 5 or 6 mm. farther on when 

 it bifurcates into dorsal and ventral hepatic arteries. The dorsal 

 hepatic artery passes straight to the posterior end of the liver and 

 then turns anteriorly along the dorsal surface of this organ on the 

 right of the vein formed by the union of the abdominal and portal 

 veins. Besides supplying the liver this vessel also sends branches to 

 the ventral stomach wall, which pass along the mesentery together 

 with the factors of the above-mentioned vein returning the blood 

 from this section of the stomach-wall. There are usually two arterial 

 branches to each venous factor. A small cystic artery to the gall- 

 bladder also arises from this branch. 



The ventral hepatic artery sends numerous branches to the duo- 

 denum in the region of the bile-duct, and then loops round the duct 

 to enter the liver immediately ventral to it. 



(/) The A. duodeno-pancreatica (a.d-pan.) or A. mesenterica prima 

 (Hyrtl, Osawa) which passes through the pancreas proximal to the 

 portal vein, and besides giving off considerable branches to the gland 

 itself is distributed to the proximal region of the duodenum. 



id) The mesenteric branches (a.mes.a.) of the coeliaco-mesenteric 

 artery which vary from two to four in number. They leave the artery 

 posteriorly, the last one coming off very soon after its origin from 

 the dorsal aorta, and are distributed to the proximal portion of 

 the intestine. 



After the large coeliaco-mesenteric vessel just described there 

 arise from four to eight anterior mesenteric arteries (a.mes.a.) (AA. 

 mesenteriae accessor'iae — Osawa). These are given off serially from 

 the section of the dorsal aorta corresponding approximately with the 

 eleventh to the fourteenth vertebrae inclusive, and supply the distal 

 portion of the intestine as far as the rectum, frequently spreading 

 over the anterior end of this also. The interval between these vessels 

 is only about a millimetre or a little more, and they tend to run 

 obliquely forwards through the mesentery so as to be gathered to- 

 gether into a bundle just posterior to the coeliaco-mesenteric artery. 

 They then bend back posteriorly to their distribution. 



Distinguishable from the foregoing only by the fact that they arise 

 after an interval of about 5 mm., and that they are not grouped quite 

 so closely into a bundle, are about three posterior mesenteric arteries 

 (a.mes.p.). They enter the dorsal side of the rectum. The interval 

 between the origins of these vessels is rather greater than between 



