90. =Triangular ligament.=--In a thin perineum, we can feel the lower border of the deep perineal fascia or the ‘so-called’ triangular ligament of the urethra. The urethra passes through it about one inch below the lower part of the symphysis pubis, and about three-quarters of an inch higher than the central tendon of the perineum. It is important to bear in mind these landmarks in introducing a catheter. If the catheter be depressed too soon, its passage will be resisted by the triangular ligament; if too late, it will be likely to make a false passage by running through the bulb. 91. =Anus.=--One of the most important landmarks which guide a surgeon in his operations about the anus, is a white line[6] at the junction of the skin and mucous membrane. It is easily recognised and is of especial interest, because it marks with great precision the linear interval between the external and internal sphincter muscles. From this line the internal sphincter extends upwards, beneath the mucous membrane, for about an inch, becoming gradually more and more attenuated. The wrinkled appearance of the anus is caused by the contraction of the external sphincter. At the bottom of these cutaneous folds, especially towards the coccyx, we look for ‘fissure of the anus.’ 92. =Landmarks in the rectum.=--Many valuable landmarks may be felt by introducing the finger into the rectum, with a catheter at the same time in the urethra. The principal of these landmarks are the following:-- _a._ The finger can feel the extent and powerful grasp of the internal sphincter for about one inch up the bowel. (91) _b._ =Urethra.=--Through the front wall of the bowel it can most distinctly feel the track of the membranous part of the urethra, exactly in the middle line. This is very important, because you can ascertain with precision whether the catheter has deviated from the proper track. _c._ =Prostate gland.=--About an inch and a half or two inches from the anus, the finger comes upon the prostate gland. The gland lies in close contact with the bowel, and can be detected by its shape and hard feel. The finger, moved from side to side, can examine the size of its lateral lobes, their consistence and sensibility. _d._ The finger, introduced still farther, can reach beyond the prostate, as far as the apex of the trigone of the bladder. More than this, it can feel the angle between the ‘ductus communes ejaculatorii,’ which forms the apex of the trigone. This is the precise spot where the distended bladder should be punctured through the rectum. The more distended the bladder, the easier can this spot be felt. Fluctuation is at once detected by a gentle tap on the bladder above the pubes (86). The trochar must be thrust in the direction of the axis of the distended bladder; that is, roughly speaking, in a line drawn from the anus through the pelvis to the umbilicus.