1228 THE DIGESTIVE SYSTEM. 



General Relations of the Rectum (Figs. 959 and 960). Posteriorly, the rectum 

 rests on the front of the sacrum and coccyx, and below them upon the posterior part 

 of the pelvic floor formed by the meeting of the two levatores ani in the ano- 

 coccygeal raphe. When much distended it also comes into relation, on each side, 

 with the lower part of the piriformis and the sacral plexus, but is separated from 

 them by a very considerable amount of connective tissue, arranged (apparently in 

 several layers) around the tube. In this tissue the two chief branches of fhe 

 superior hsemorrhoidal vessels lie behind the superior part of the bowel, but lower 

 down they are placed in relation to its sides. 



At its sides above are the pararectal fossae and their contents (pelvic colon, or 

 ileum) ; below the pararectal fossae the rectum is in contact with the coccygei and 

 levatores ani muscles, which run backwards to the coccyx on each side of the 

 bowel. The branches of the superior haemorrhoidal vessels are also found running 

 down on its muscular coat, as far as the middle of the rectum, where they pierce 

 the wall of the bowel. 



Anteriorly, in the male the rectum is separated from the bladder, to within an 

 inch of the prostate, by the recto-vesical pouch of peritoneum, which usually 

 contains some coils of small intestine. Below the reflection of the peritoneum the 

 front of the bowel is in contact with the posterior aspect of the bladder, the deferent 

 ducts, vesiculae seminales, and the posterior aspect of the prostate gland (Fig. 

 960), from all of which it is separated by the recto-vesical layer of the pelvic fascia. 



The lower portions of the rectum and bladder in the male are separated by the 

 recto-vesical fascia only, over a narrow triangular area which measures about an 

 inch (2'5 cm.) in vertical height. The base of the triangle corresponds to the 

 reflection of the peritoneum from one organ to the other, and the apex to the 

 union of the sides formed by the deferent ducts, which lie very close to one 

 another except above, near the base of the triangle, where they diverge rather 

 abruptly (Fig. 960). Through the triangle the operation <of tapping the bladder 

 from the rectum used to be performed. 



The vesiculse seminales, unless when of a small size, slope laterally and posteriorly 

 round the front and sides of the distended rectum (Fig. 960), which they thus embrace, 

 as it were, within their grasp. 



The ureters, as they run medially towards the base of the bladder, lie close in front of 

 the deferent ducts, and are not far separated from the distended rectum (see Fig. 960). 



In the female the rectum is separated from the posterior surface of the uterus 

 and the upper end of the vagina by the recto-uterine pouch and the intestine 

 which it usually contains. Below the peritoneal reflection it is in direct contact 

 with the posterior vaginal wall, to which it is connected loosely above, but more 

 closely below. 



The portion of the rectum below the level of the peritoneal reflection is surrounded 

 by the rectal fascia, a layer of connective tissue which is derived from the visceral 

 layer of the pelvic fascia. 



In the child the rectum, or at least its superior part, is relatively larger, and it pursues 

 a much straighter course than in the adult. As pointed out above, its peritoneal covering 

 likewise descends lower at birth, and reaches as far as the base of the prostate. 



PAES ANALIS RECTI ANAL CANAL. 



Pars Analis Recti. In order to reach the exterior, it is necessary for the 

 lower end of the bowel to pierce the floor of the pelvis. This it does by passing 

 through the narrow interval left between the medial borders of the levatores ani 

 muscles (Fig. 963). As it passes between them, the two muscles pinch in the 

 tube, and by the apposition of its side walls obliterate its cavity, reducing it to 

 a mere slit-like passage. This passage, through which the rectum communicates 

 with the exterior, is the " anal canal " (Symington). 



The term pars analis recti refers, strictly, to the lower half only of this canal 

 which is lined by squamous epithelium, and shows the columnas rectales. 



