400 DISSECTION OF THE PERIN2EUM. 



urethra, opening the canal, and slitting that tube and the neck of the 

 bladder. In the external incisions the knife is entered in the middle 

 line of the perinaeum, half an inch in front of the anus, and is drawn back- 

 wards on the left side as far as midway between the ischial tuberosity and 

 the anus. The skin and superficial fascia, and the inferior hemorrhoids! 

 vessels and nerve lying across the ischio-rectal fossa, will be cut in this 

 first stage of the operation ; and the transverse perinatal muscle and artery, 

 and, possibly, the superficial perinasal vessels and nerves, may be divided, 

 if the first incision is begun farther forwards. 



In the subsequent attempt to reach the staff, when the knife is intro- 

 duced into the anterior part of the wound, the lower part of the triangular 

 ligament, the deep transverse urethral muscle, and the fore part of the 

 levator ani will be divided ; and when the knife is placed within the groove 

 of the staff, the membranous part of the urethra will be cut, with the 

 muscular fibre about it. 



Lastly, as the knife is pushed along the staff into the bladder, it incises 

 in its progress the membranous portion of the urethra, part of the prostate 

 with large veins around it, and the neck of the bladder. When the last 

 two parts are being cut, the handle of the knife is to be raised, and the blade 

 depressed ; and the incision is to be made downwards and outwards in the 

 direction of a line from the urethra through the left lateral lobe of the 

 prostate, above the level of the ejaculatory duct. 



Parts to be avoided. In the first incisions in the ischio-rectal fossa, 

 the rectum may be cut if the knife is turned inwards across the intestine, 

 instead of being kept parallel with it ; and if the gut is not kept out of the 

 way with the fore finger of the left hand. The pudic vessels on the outer 

 wall of the ischio-rectal fossa can be wounded near the anterior part of the 

 hollow, where they approach the margin of the triangular ligament ; but, pos- 

 teriorly, they are securely lodged inside the projection of the tuber ischii. 



Whilst making the deeper incisions to reach the staff, the artery of the 

 bulb lies immediately in front of the knife, and will be wounded if the in- 

 cisions are made too far forwards ; but the vessel must almost necessarily 

 be cut, when it arises farther back than usual, and crosses the front of the 

 ischio-rectal fossa in its course to the bulb of the urethra. 



In the last stage ot the operation the neck of the bladder should not be 

 cut to a greater extent than is necessary for the extraction of the stone, 

 lest the recto-vesical fascia separating the perinaeum from the pelvis should 

 be divided, and the abdominal cavity opened. Too large an incision 

 through the prostate may wound also an unusual accessory pudic artery 

 on the side of that body. 



Directions. When the dissection of the perinaeum is completed, the 

 flaps of skin are to be fastened together, after salt has been used, and the 

 limbs are to be put down for the examination of the abdomen. 



SECTION II. 



PERINEUM OF THE FEMALE. 



THE perinaeum in the female differs from that in the male more in the 

 external form than the internal anatomy. On the surface it has special 

 parts distinguishing it, viz., the aperture of the vagina, and the opening of 

 the vulva with the labia. 



