1042 



THE ORGANS OF DIGESTION. 



neum is reflected upon the bladder, i. e. 6 to 8 cm. above the anal orifice. It is 

 historical, and has been described by Ndlaton and Yelpeau as sphincter superior ; 

 as Houston's "most frequent" valve; as Hyrtl's sphincter tertius ; and Kohl- 

 rausch's plica transversalis. This extends from the right to the anterior Avail of 

 the rectum, and cannot be obliterated, as it does not contain longitudinal muscu- 

 lar fibres. It projects 15 mm. into the lumen of the gut and extends around one- 

 half or two-thirds of its inner circumference (Fig. 659). There are generally two 

 other folds on the left side, one about one inch above and the other one inch 

 below, this one of the right side. These two contain all the coats of the wall and 

 may be obliterated by distention. Note the tendency of the three to the forma- 

 tion of a spiral valve. They may all be called valves or folds of Houston. The 

 dilatation between the lowest valve and the anal canal is the rectal ampulla. 

 The presence of these valves may cause difficulty in the passage of bougies or in 

 digital examinations. In function they seem to assist the sphincters and act as 

 shelves in supporting the fgecal masses. 



In the anal canal the mucous membrane is thrown into three to eight longi- 



D O 



tudinal folds containing muscular fibres, probably of the muscularis mucosae ; 

 they are called columnce ani or columns of Morgagni. They commence just above 

 the anal orifice and extend 7 to 14 mm. up the anal canal, rising 1 to 2 mm. 

 above the level of the mucous membrane. Stretched between these columns at 

 their inferior extremities are semilunar valves or folds made of mucous membrane 

 with concavities turned upward. They are unequal in length, varying inversely 

 with the number of columns. 



Behind each valve and between any two contiguous columns is a little con- 

 cavity or sinus with mouth directed upward. Thus, there are columns, valves, 

 and sinuses of Morgagni (Fig. 660). 



Column of Morgugni 



Sinus of Morgagni 

 Valve of Morgagni 



FIG. 660. Mucous membrane of anal canal showing columns, valves, and sinuses of Morgagni. (Schematic.) 



The characteristic cells of the mucous membrane are cylindrical epithelium. 

 The glands present are those of Lieberkiihn and the solitary lymph-follicles. 

 Inferiorly on the anal canal there is a narrow zone of mucous membrane desti- 

 tute of glands. 



Vessels and Nerves of the Rectum. The arteries spring from five or six 

 sources, three of which are named hsemorrhoidal : the superior hcemorrhoidal 

 from the inferior mesenteric artery ; the middle hcemorrhoidal from the internal 

 iliac ; and the inferior hcemorrhoidal from the internal pudic. The sacra media 

 and sciatic arteries also send unnamed branches to the rectum, and in the female 

 the vaginal artery does the same. These arteries coming from above form loops 

 on either side of the rectum with convexities pointing downward. These are 

 three or four inches above the anus ; from these loops several branches rise, and 

 pass longitudinally downward, pierce the muscular coats and enter the submu- 

 cosa, and anastomose freely. In the anal canal they are longitudinal in folds of 

 mucous membrane, and reach to the anal orifice. 



The veins return the blood in a similar way, starting by dilatations below and 

 making a plexus higher up under the mucous membrane. Most of this blood is 

 returned by the superior hsemorrhoidal vein to the inferior mesenteric vein and 

 portal system. The rest of it reaches the systemic circulation and vena cava infe- 

 rior. The rectum furnishes an anastomosis between these two systems. It is very 

 strange that the anatomical text-books apply the term hcemorrhoidal to all vessels 



