Arteries.—In Compartments I and II there are no special points of clinical interest in connexion with the arterial arrangements. The arteries are derived from those supplying structures in the vicinity.
In the remainder of the alimentary tube, i.e., the abdominal part, the distribution of the arteries is highly specialized. This accords with the observation that when the distribution of the branches o f a large artery is confined to a particular region, that region is a physiological unit and not merely an anatomical one (Fig. 4).
The walls of Compartment III are supplied by the cœliac artery (Fig. 5 ) ; included in the term ‘walls’ are the large glands of this region, namely, spleen, liver, and pancreas. Of the three branches of the cœliac artery: (1) The lienal (splenic) goes to the spleen, the pancreas, and thgreater curvature of the stomach (left gastro-epiploic). (2) The left gastric branch runs along the lesser curvature of the stomach to meet and anastomose with branches of the hepatic. (3) T h e hepatic artery has an extensive distribu- tion : one of its main branches runs through the portal fissure to be distributed to the liver; the other main branch—the gastroduodenal—divides into (a) the right gastro-epiploic that links with the left gastro-epiploic to assist in the supply of the stomach and the pancreas, and (b) the superior pan- creaticoduodenal that contributes to the arterial supply of the pancreas and the proximal half of the duodenum. In passing, it may be noted that, in comparison with the rest of the stomach, the arterial supply of the lesser curvature is poor, and that of the duodenal cap very poor.
It will be obvious, therefore, that the whole arterial supply of Compartment III is entrusted to the coeliac artery.
The arterial supply of Compartment IV is allotted to the superior mesenteric artery (Fig. 6). Through its upper branches this artery, by its anastomoses with the superior pancreatico- duodenal, completes the supply of the duodenum and the head of the pancreas. Then by a series of arterial arches it provides a very rich arterial supply for the whole length of the jejunum and ileum. An ileocolic branch is distributed to the ileocolic region, caecum, and appendix, and anastomoses with the right colic branch to the ascending colon and right colic flexure. This right colic branch joins up with the middle colic, which continues the regional distribution of the superior mesenteric to the middle of the transverse colon.
Special notice should be taken of the extremely rich vascular supply of the jejunum and ileum (and particularly of the jejunum), which is obviously related to the great functional activity of these parts. A progressive decrease in vascularity is evident from the jejunum to the ileocolic region; by com- parison, the relative poverty of the blood-supply to the great intestine is very suggestive.
Compartment V derives its arterial supply from the inferior mesenteric artery (Fig. η). The left colic branch of this artery anastomoses with the middle colic branch of the superior mesenteric and supplies the left half of the transverse colon, the left colic flexure, and the descending colon. Sigmoid branches supply the iliac colon and pelvic colon. The inferior mesenteric artery is continued on to the rectum as the superior haemorrhoidal.
As in Compartments I and II, the arterial supply of Com- partment VI is of minor clinical importance; it is derived chiefly from the middle and inferior haemorrhoidal arteries.
Veins.—The venous drainage of Compartments I, 77, and VI does not call for special comment.
The whole venous drainage of Compartments III, IV, and V is directed into the liver through the portal vein (Fig. 8) ; the blood from the liver is conveyed by the hepatic veins directly into the inferior vena cava.
Compartment III is drained by the lienal, coronary, pyloric, right gastro-epiploic, and pancreatico-duodenal veins. The veins of Compartment IV ultimately discharge their blood into the superior mesenteric vein which joins the lienal vein to form the portal vein.
In Compartment V the venous blood finds its way into the inferior mesenteric vein which ends in the lienal vein.
The tributaries of the superior and inferior mesenteric veins correspond closely to the branches of the superior and inferior mesenteric arteries. At the periphery of the portal system of veins small connexions are formed with (a) oeso- phageal veins, (b) veins in the ligamentum teres of the liver, and (c) veins in the lower end of the rectum and anal canal.