40 LANDMARKS MEDICAL AND SURGICAL. 



THE PERINEUM. 



The body is supposed to be placed in the usual position 

 for lithotomy. 



87. Bony framework. We can readily feel the osseous 

 and ligamentous boundaries of the perineum ; namely, the 

 rami of the pubes and ischia, the tuberosities of the ischia, 

 the great sacro-ischiatic ligaments, and the apex of the 

 coccyx. This framework forms a lozenge-shaped space. If 

 we draw an imaginary line across it from the front of one 

 tuber ischii to the other, we divide this space into an anterior 

 and a posterior triangle, The anterior is nearly equilateral, 

 and, in a well-formed pelvis, its sides are from three to three 

 and a half inches long. It is called the urethral triangle. 

 The posterior, containing the greater part of the anus and the 

 ischio-rectal fossa on each side, is called the anal triangle. 



88. Baphd. A slight central ridge of skin, called the 

 ' raphe,' runs from the anus up the perineum, scrotum, and 

 penis. This ' raphe,' or middle line of the perineum, is the 

 'line of safety' in making incisions i to let out matter or 

 effused urine, or to divide a stricture. 



89. Central point of perineum. It is very important to 

 know that a point of the raphe about midway between the 

 scrotum (where it joins the perineum) and the centre of the 

 anus, corresponds with the so-called ' central tendon ' where 

 the perineal muscles meet. The bulb of the urethra lies 

 above this point, and never, at any age, comes lower 

 down. The artery of the bulb, too, never runs below this 

 level. Therefore the incision in lithotomy should never com- 

 mence above it. A knife introduced at this point, and pushed 

 backwards with a very slight inclination upwards, would enter 

 the membranous part of the urethra just in front of the pros- 

 tate gland ; pushed still farther it would enter the neck of the 

 bladder. This point, then, is a very good landmark to the 

 urethra in lithotomy, or, indeed, in any operations on the 

 perineum. 



The incision in the lateral operation of lithotomy, begin- 

 ning below the point indicated, should be carried downwards 



