RECTUM AND ANAL CANAL. 



441 



anal canal. They anastomose with the middle and superior hemorrhoidals. They 

 are distributed more to the posterior portion of the lower part of the rectum and anal 

 canal while the middle is distributed more to its anterior portion. 



The middle sacral artery passes down in the median line from the bifurcation of 

 the aorta to the tip of the coccyx, where it ends in Luschka's gland. It gives a few 

 branches to the rectum at its upper part but they are supposed not to go deeper than 

 the muscular coat. It anastomoses with the superior hemorrhoidal. 



Veins. The veins of the rectum and anal canal accompany the corresponding 

 superior, middle, and inferior hemorrhoidal arteries. They form two plexuses, an 

 internal submucous plexus and an external plexus on the surface of the rectum. The 

 internal plexus in the submucous coat begins at the anus in fine venous capillaries 

 which pass upward, mainly in the columns of Morgagni, where they form small dila- 

 tations or pools and unite into larger branches which pierce the muscular walls about 

 the middle of the rectum to empty into the main superior hemorrhoidal veins and 

 thence into the inferior mesenteric. 



The inferior hemorrhoidal veins receive branches from the anus and outer surface 



FIG. 447. Lymphatics of rectum. (Gerota.) 



of the sphincters and levator ani muscles and pass thence to the internal pudic veins. 



The middle hemorrhoidal vein drains the blood from the external hemorrhoidal 

 plexus on the outer surface of the lower half of the rectum and empties into the inter- 

 nal iliac. It anastomoses with the superior hemorrhoidal above, at about the middle 

 of the rectum, and the inferior hemorrhoidal below, at the upper portion of the anal 

 canal. It is thus seen that the interior of the lower half of the rectum is drained by 

 the superior hemorrhoidal and its exterior by the middle hemorrhoidal. The blood 

 from the upper part of the anal canal drains into the superior hemorrhoidal, that 

 from its lower part into the inferior hemorrhoidal. The blood from the superior 

 hemorrhoidal veins empties into the portal system through the inferior mesenteric, 

 and the blood from the middle and inferior into the general venous system through 

 the internal pudic, internal iliac, and inferior cava. These veins are usually regarded 

 as being without valves, though the opposite view is held by some. 



Lymphatics. According to Poirier andCuneo there is a superior group accom- 

 panying the superior hemorrhoidal vessels and draining the mucous membrane of the 

 anal canal and rectum and terminating in the nodes of the pelvic mesocolon after 

 traversing the pararectal lymph-nodes ; also a middle group partly communicating 



