THE PERINEUM. 41 



and outwards between the anus and the tuberosity of the 

 ischium, a little nearer to the tuberosity than the anus. The 

 lower end of the incision should reach a point just below the 

 anus. 



90. Triang-ular lig-ament. 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 land- 

 marks may be felt by introducing the finger into the rectum, 

 with a catheter at the same time in the urethra. The prin- 

 cipal 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. 



