MOVEMENTS AND INNERVAT1ON OF THE INTESTINES 1313 



ORRHOIOAL 



MIDDLE 



HEMORRHOIDAl. 



ARTERY 



left colic branch of the inferior mesenteric, and the sigmoid flexure by the sigmoid branches 

 of the inferior mesenteric. The rectum (Fig. 1056) is supplied mainly by the superior hemor- 

 rhoidal branch of the inferior mesenteric, but also at its lower end by the middle hemorrhoidal 

 from the internal iliac, and the 

 inferior hemorhoidal from the 

 internal pudic artery. The 

 superior hemorrhoidal, the con- 

 tinuation of the inferior mesen- 

 teric, divides into two branches, 

 which run down either side of the 

 rectum to within about five inches 

 (12.5 cm.) of the anus; they here 

 split up into about six branches, 

 w y hich pierce the muscular coat 

 and descend between it and the 

 mucous membrane in a longitu- 

 dinal direction, parallel with each 

 other as far as the Internal 

 sphincter, where they anastomose 

 with the other hemorrhoidal arte- 

 ries and form a series of loops 

 around the anus. The veins of 

 the large intestine correspond to 

 the arteries and join the superior 

 and inferior mesenteric veins 

 which join the portal vein. The 

 veins of the rectum (Fig. 1056) 

 commence in a plexus of vessels 

 which surrounds the lower ex- 

 tremity of the intestinal canal. 

 In the vessels forming this 

 plexus are small saccular dilata- 

 tions just within the margin of 

 the anus (Figs. 1054 and 1056); 

 from it about six vessels of con- 

 siderable size are given off. 

 These ascend between the mus- 

 cular and mucous coat for about 

 five inches (12.5 cm.), running 

 parallel to each other; they then 

 pierce the muscular coat, and, 

 by their union, form a single 

 trunk, the superior hemorrhoidal 

 vein, which empties into the 

 inferior mesenteric tributary of 

 the portal vein. This arrange- 

 ment is termed the hemorrhoidal 

 plexus (Fig. 524); it communi- 

 cates with the tributaries of the 

 middle and inferior hemorrhoidal 



veins at its commencement, and thus a communication is established between the systemic 

 and portal circulations. The inferior hemorrhoidal veins empty into the internal pudic 

 veins, and the middle hemorrhoidal veins empty into the internal iliac veins. 



The lymphatics of the large intestine are described on page 797. 



The nerves are derived from the sympathetic plexuses around the branches of the superior 

 and inferior mesenteric arteries. They are distributed in a similar way to those found in the 

 small intestine. The spinal centre for the nerves of the anus and rectum is situated in the first 

 and second sacral segments of the spinal cord. 



INFERIOR 



HEMORRHOIDAL 



ARTERY 



FIG. 1056. The bloodvessels of the rectum and anus, showing the 

 distribution and anastomosis on the posterior surface near the termi- 

 nation of the gut. (Poirier and Charpy.) 



Movements and Innervation of the Intestines. 



Movements. As the small intestine is devoid of any sphincter arrangement, peristalsis cannot 

 mix the food as it does in the pyloric portion of the stomach. The process by which the food is 

 mixed with the secretions and is brought against the intestinal wall for absorption is called by 

 Cannon "rhythmic segmentation." Rhythmic motions "mix the food and expose it to the 



83 



