202 ANATOMY OF THE ABDOMEN, ETC. 



The legs being flexed, the thighs are to be bent upon the trunk, anc 

 the nates made to project over the edge of the table, preserving then 

 position by one or two turns of a cord carried round the right knee, 

 then under the table to the left knee, and finally made fast by agaii 

 attaching it to the right knee. The subject being thus placed,"tht 

 scrotum and testicles should be lifted on to the pubes, and kept oul 

 of the way by hooks or pins ; the rectum is to be distended wit! 

 cotton wool, tow, or similar material, and, when well filled, the anus 

 should be made to project by pressing it downward from within tin 

 pelvis. The perineum being washed and shaved, is then ready for 

 dissection. An elliptical incision, commencing at the root of the 

 scrotum, its long diameter corresponding to the median line, shoulc 

 include the anus, and extend to the coccyx posteriorly ; the integu- 

 ineiit is then to be dissected toward the anus. 



The PERINEUM is an important surgical region, bounded 

 on each side by the tuberosities of the ischia, in front by 

 the arch of the pubes, and behind by the coccyx ; in other 

 words, its boundaries are those of the inferior strait of the 

 pelvis. 



Immediately beneath the skin, where it becomes continu- 

 ous with the mucous surface of the anus, the fibres of the 

 sphincter ani will present themselves, pale in color, and 

 indistinctly characterized. Elsewhere, a layer of fat and 

 cellular tissue, constituting the superficial fascia, covers 

 in the deeper parts of the perineum ; laterally, between the 

 anus and the ischia this is considerable in amount, and fills 

 a large space, called the ischio-rectal fossa. 



The superficial fascia, consisting of two layers, is con- 

 nected laterally with the rami of the ischia and the pubes, 

 but through the medium of the scrotum becomes continuous 

 with the corresponding structure in the groin (pp. 168 and 

 195). Posteriorly, it dips down in front of the rectum to 

 join the anterior layer of the triangular ligament, or deep 

 fascia of the perineum. Hence, abscesses of this region, or 

 extravasation of urine from rupture of the urethra, do not 

 extend backward behind the rectum, or laterally upon th 

 thighs, but forward toward and into the scrotum, and even 

 to the anterior part of the abdomen. In and beneath this 

 fascia will be found a number of vessels and nerves. 



The external hemorrhoidal artery traverses the ischio- 

 rectal fossa ; it is an offset from the internal pudic artery, 

 a branch of the internal iliac, which lies under the ramus 

 of the ischium, and is distributed to the sphincter and 

 levator ani muscles and to the lower part of the rectum. 

 Farther in front, the internal pudic artery gives off the 



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