THE MUSCLES AND FASCL-E OF THE RECTUM AND ANUS. 1679 



Fig. 1427. 



Internal hemorrhoidal vein 



Levator ani 



Mucous 

 membrane 



Peritoneal Relations of the Rectum. — The posterior surface of the highest 

 part of the rectum is usually coated like the rest with peritoneum, except near the 

 median line ; but this narrow retroperitoneal surface enlarges rapidly, so that soon 

 the entire posterior surface in the hollow of the sacrum and coccyx is without serous 

 covermg. The gut rests on the dense rectal fascia. The sides and front of the 

 rectum are covered with peritoneum, which is reflected laterally, first onto the sides 

 of the posterior wall of the pelvis, then onto the floor. The peritoneum forms a 

 deep pouch in front of the rectum, known from its anterior wall as the redo-vesical 

 in the male and the redo-ziterine, or the pouch of Douglas, in the female. In man 

 this pouch separates the rectum from the bladder and the upper part of the semmal 

 vesicles and in woman from the upper part of the vagina. The distance of the line 

 of reflection of peritoneum — that is to say, the bottom of the pouch — from the ano- 

 rectal groove may be as little as 5 cm. (2 in.), as usually given ; if, however, by the word 

 ' ' anus' ' be understood what is practically the orifice of the gut, the distance is nearly 

 7 cm. (2^ in.) in both sexes. If both bladder and rectum be distended, the pouch 

 is considerably raised; when the rectum is collapsed, it contains loops of the small in- 

 testine or the sigmoid flexure. The 

 redo-vcsical folds in the male, although 

 described with the bladder (page 1 905) , 

 should be mentioned here. They are 

 reckoned among the false ligaments 

 of the bladder, and bound laterally 

 the pouch just described ; extending 

 backward from the bladder around 

 the rectum to the sides of the sacrum, 

 they tend to divide the cavity of the 

 pelvis into an upper and a lower com- 

 partment. Their free edges are semi- 

 lunar and sharp, and curve around 

 the rectum above the ampulla, which 

 they partially roof in. These liga- 

 ments contain more or less fibrous 

 tissue. In the female they are less 

 developed, although important, and, 

 arising from the uterus instead of the 

 bladder, are known as the sacro-2iterine 

 folds. 



Blood-Vessels. — The arteries 

 supplying the rectum are derived 

 chiefly from the three hemorrhoidals. 

 The superior hemorrhoidal, the ter- 

 mination of tjie inferior mesenteric 

 artery, divides opposite the sacrum, 



sometimes near the beginning of the rectum, sometimes higher, and even above the 

 pelvis, into two branches, of which the right is the larger, that descend on either side 

 of the rectum and give off smaller branches. A median posterior branch usually 

 arises from the right one. The mucous membrane is supplied by these above the 

 boundary line. Vessels may be received also from the sacra media. The middle 

 hemorrhoidal arteries, of uncertain origin and distribution, rarely give any consider- 

 able supply to the gut. The inferior hemorrhoidals — two or three small branches 

 from the internal pudic — supply chiefly the external sphincter, but also form a num- 

 ber of fine anastomoses with the superior hemorrhoidal artery. The general dis- 

 tribution of the vejyis is not very different from that of the arteries. The superior 

 hemorrhoidal veins, tributaries of the inferior mesenteric, drain into the portal system. 

 They form a very rich plexus throughout the rectum, particularly in the upper and 

 middle parts of the anal canal. In this situation they present a series of dilatations 

 encircling the gut on the bases of the columns of Morgagni, just above the boundary 

 line between the mucous and cutaneous areas ; this line also marks the parting of 

 the ways between the superior and external hemorrhoidal veins. The latter form 



Middle 



hemorrhoida 



vein 



Internal 

 sphincter 



Externa 

 sphincter 



Groove 



External 

 hemorrhoidal 

 vein 



Frontal section of wall of anal canal, showing relations of 

 hemorrhoidal veins. (Otis.) 



