THE ANAL CANAL. 1041 
muscles, which run backwards to the coceyx on each side of the bowel. The 
branches of the superior hemorrhoidal 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. 
In front, the rectum is separated from the bladder, to within an inch of the 
prostate, by the rectovesical pouch of peritoneum, which usually contains some 
coils of small intestine. Below the reflexion of the peritoneum the front of the 
bowel is in contact with the base of the bladder, the vasa deferentia, vesiculee 
seminales, and the back of the prostate gland Cn. 702), from all of which it is 
separated by the rectovesical layer of the pelvic fascia. In the female (Fig. 707) 
the rectum is separated from the posterior surface of the uterus and the upper 
end of the vagina by the pouch of Douglas and the intestine which it usually 
contains. Below the ‘peritoneal reflexion it is in direct contact with the posterior 
vaginal wall, to which it is connected loosely above, but more closely below. 
The lower portions of the rectum and bladder in the male are separated by the 
rectovesical fascia only, over a narrow triangular area which measures about an 
inch (2°56 cm.) in vertical height. The base of this triangle corresponds to the 
reflexion of the peritoneum from one organ to the other, and the apex to the 
base of the prostate, whilst the sides are formed by the vasa deferentia, which he 
very close to one another except above, near the base of the triangle, where they 
diverge rather aby ‘uptly (Fig. 702). Through this triangle the operation of 
tapping the bladder from the rectum is performed. 
The vesiculze seminales, unless when of a small size, slope outwards and backwards round 
the front and sides of the distended rectum (Fig. 702), which they thus embrace, as it 
were, within their grasp. 
The ureters, as they run inwards towards the base of the bladder, lie close in front of 
the vasa deferentia, and are not far separated from the distended rectum (see Fig. 702). 
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 upper 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. 
THE ANAL CANAL. 
Anal Canal (pars analis recti—third part of the rectum of the old deserip- 
tions).—In order to reach the exterior, it 1s 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 mesial borders of the levatores ani muscles 
(Fig. 701). As it passes between them, the two muscles pinch in the tube, and by 
the apposition of its lateral walls obliterate its cavity, reducing it to a mere slt- 
like passage. This passage, through which the rectum communicates with the 
exterior, is the “anal canal” (Symington). 
Formerly this terminal portion of the tube was described as the “ third part of the rectum,” 
and, like the rest of that bowel, it was supposed to form a reservoir for the retention of the 
feeces. Symington pointed out that this was not the case. He showed that the canal was not 
of the same nature as the rest of the rectum, but that it was a mere passage through which the 
bowel discharged its contents, the relation between the two being practically the same as that 
between the urethra and the bladder in the female. It is probable, however, that, when the rectum 
is distended, the upper part of the anal canal is often, if not usually, occupied by the wedge- 
shaped lower end of the contained fecal mass, whilst the chief bulk of the contents is supported 
by the rectal valves and the levatores ani, 
The anal canal begins where the rectum proper terminates, namely, at the 
Jevel of the levatores ani muscles, opposite the lower part of the prostate. 
When the distended rectum is cut across near its lower end, in a hardened body, 
and the cavity examined from the interior, a distinct projection, formed by 
the inner border of the levator ani (pubo-rectalis, or sphincter recti portion), is 
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