_e._ The fold of peritoneum, called the recto-vesical pouch, is about four inches from the anus, therefore it is not within reach of the finger; and we run no risk of wounding it in tapping the bladder if the trochar be introduced near the angle of the trigone. _f._ The finger can feel one of the ridges or folds of mucous membrane which are situated at the lower part of the rectum. This fold projects from the side, and sometimes from the upper part of the rectum, near the prostate. When thickened or ulcerated, this fold occasions great pain in defæcation; and great relief is afforded by its division. _g._ Lastly, the finger can examine the condition of the spaces filled with fat on either side of the rectum, called the ischio-rectal fossæ, with a view to ascertain the existence of deep-seated collections of matter, or the internal communications of fistulæ. =Introduction of catheters.=--In the introduction of catheters the following are good rules. Keep the point of the instrument well applied against the upper surface of the urethra;--depress the handle at the right moment (90);--keep the umbilicus in view;--in cases of difficulty feel the urethra through the rectum, to ascertain whether the instrument be in the right direction. Attention to these rules diminishes the risk of making a false passage, an injury which under great delicacy in manipulation ought never to happen. =Urethra in the child.=--In children the membranous part of the urethra is, relatively speaking, very long, owing to the smallness of the prostate. It is also more sharply curved, because the bladder in children is more in the abdomen than in the pelvis. It is, moreover, composed of thin and delicate walls. The greatest gentleness, therefore, should be used in passing a catheter; else the instrument is likely to pass through the coats and make a false passage. Hence the advantage of being able to ascertain through the rectum whether the instrument be in the right track and moving freely in the bladder, which can also be easily felt in children. _THE THIGH._ 93. =Poupart’s ligament, or crural arch.=--Mark the anterior superior spine of the ilium, the spine of the pubes, and define the line of ‘Poupart’s ligament’ which extends between them. This line is one of our guides in the diagnosis of inguinal and femoral herniæ. If the bulk of the tumour be above the line, the hernia is probably inguinal; if below it, femoral. The line is not a straight one drawn from the spine of the ilium to the spine of the pubes, but slightly curved, with the convexity downwards, owing to its close connection with the fascia lata of the thigh. In many persons it can be distinctly felt; in nearly all its precise course is indicated by a slight furrow in the skin. For the points about the spine of the pubes, refer to paragraph 69.