The rectum, like the rest of the alimentary canal, is freely supplied with blood. Its arte ries are named henzorrhoidal, and are derived from three sources, viz., the abdominal aorta, the internal iliac, and the internal pudic arte ries. The superior ha morrhoidal is the con tinuation of the inferior mesenteric, a branch of the aorta ; the middle hemorrhoidal is derived either from the internal iliac or from some of its branches ; and the inferior or external he morrhoidal branches from the perinceal division of the pudic. The latter are destined directly to the confines of the anus, and are lodged in the subcutaneous adeps. The two former be long properly to the rectum, and are above the levatores ani muscles. These arteries divide into several small branches, which anastomose together, and form a continued chain of inos culations along this intestine, somewhat similar to that which is continued along the whole of the alimentary tube. They form a complicated vascular net-work between and within the mus cular fibres, and are largely distributed to the mucous and submucous tissues. Some branches of considerable size not unfrequently descend so low even as the sphincter, particularly at its posterior parts. These are liable to be divided in operations for the cure of fistulae, and some times give rise to a haemorrhage, troublesome and difficult to restrain. In such operations the external hwmorrhoidal arteries also are very commonly opened, and bleed smartly ; they can. be secured, however, with much less difficulty than the divided extremities of the superior or middle hmmorrhoidal vessels.
The whole of the rectum, particularly its lower portion, is encompassed by numerous veins, which in some persons are very large and plexiform. In the perinwum, also, many venous plexuses are found in the subcutaneous adeps. The external hmmorrhoidal arteries have their external venze comites, which run outwardly to end in the internal pudic veins (branches of the internal iliac). Some of their branches ramify around the anus, and in some cases form a plexus, in which hemorrhoidal tumours are frequently developed ; the mid dle htemorrhoidal veins are uncertain as to number, size, and situation, but the superior are very large and numerous; their branches form repeated anastomoses in the submucous tissue around the intestine, and frequently present all the appearance of erectile tissue, particularly in front, communicating below with the perinmal veins, before with a plexus of vaginal or prostatic veins, and above with the trunk of the inferior mesenteric which leads to the vena portw. This latter communi cation, as also the absence of valves in • the portal system, has laid the foundation of the practice of applying leeches to the anal region in chronic inflammatory affections of the liver and bowels. The same facts also have been adduced to explain the frequency of haemor rhoids, varices, and vascular congestion about the anus and rectum in cases of diseased and hardened liver, which, under such circum stances, is supposed to obstruct the circulation by impeding the returning blood through the venx portx.