1058 THE DIGESTIVE SYSTEM. 4 
When viewed from the front the rectum is seen to be regularly folded from side 
to side in a zigzag fashion, the folding being slightly marked when the rectum is 
empty, but becoming much more distinct with distension (Figs. 702 and 703). In 
other words, when viewed from this aspect it presents, in the majority of cases, three 
more or less distinct lateral flexures or inflexions. Of these the upper and lower 
have their coneavities directed to the left as a rule; the third flexure, which is the 
best marked, lies between the other two, but on the right side. Not infrequently, 
however, two are found on the right and one on the left side. The flexures, which 
are marked on the exterior by a crease, appear in the interior as three prominent 
Lateral inflexions 
Upper rectal valve 
Prostatic venous 
plexus 
Ureter (cut) 
/ } \ BIE 
OUI EA 
Medene a) arilez 
Re Ds 
Vesicula seminalis White line of pelvic fascia 
Levator ani 
Vas deferens : : 
meat : ! Outline of empty bladder 
\ 
Base of prostate Urethra 
Fra. 702.—DISTENDED RECTUM IN SITU. 
From a formalin-hardened male body, age 56. The peritoneum and extra peritoneal tissue have been removed, 
after sawing the pelvis along a plane passing through the upper part of the symphysis pubis in front 
and the lower part of the second sacral vertebra behind. The bladder, which was empty and contracted, 
has also been removed, but its form is shown by a dotted line. The rectum was very much distended, 
and almost completely occupied the pararectal fosse. 
crescentic shelves (Fig. 704), known as the rectal valves, which help to support the 
feecal contents when the rectum is distended (Fig. 702). 
This folding is maintained by the arrangement of the longitudinal muscular fibres, the 
majority of which are accumulated in the form of two wide bands, one on the front, the other on 
the back of the bowel. These two bands, which are continuous with, and comparable in their 
functions to, the teenize of the colon, are shorter than the other coats of the rectum ; hence they 
give rise, as in the case of the colon, to a folding or saceulation of the tube, which can be effective 
only at the sides where the longitudinal fibres are fewest, for the front and back are occupied by 
the thickened longitudinal bands (see p. 1042). L 
In addition to supporting the feeces, these foldings greatly increase the capacity of the rectum 
without unduly dilating the tube. When the rectum is empty (Fig. 703) its course is comparatively 
straight, its lateral flexure being but slightly marked, and its whole calibre very much reduced. 
