SURGICAL ANATOMY OF THE PERINJ1UM. 



Dissection. The student should select a well-developed muscular subject, free from fat, 

 and the dissect ion should be commenced early, in order that the parts may be examined in as 

 recent a state as possible. A staff having been introduced into the bladder and the subject 

 placed in the position shown in Fig. 590, the scrotum should be raised upward, and retained in 

 that position, and the rectum moderately distended with tow. 



The Perinaeum corresponds to the inferior aperture or outlet of the pelvis. 

 Its deep boundaries are, in front, the pubic arch and subpubic ligament ; behind, 

 the tip of the coccyx ; and on each side, the rami of the os pubis and ischium, the 

 tuberositiea of the ischium, and great sacro-sciatic ligaments. The space included 

 by these boundaries is somewhat lozenge-shaped, and is limited on the surface of 

 the body by the scrotum in front, by the buttocks behind, and on each side by the 

 inner side of the thighs. A line drawn transversely between the anterior part of 

 the tuberosity of the ischium, on each side, in front of the anus, divides this space 

 into two portions. The anterior portion contains the penis and urethra, and is 

 called the perinceum proper or genito-urinary region. The posterior portion con- 

 tains the termination of the rectum, and is called the iscl do-rectal or anal region. 



ISCHIO-RECTAL EEGION. 



The ischio-rectal region contains the termination of the rectum and a deep fossa, 

 filled with fat, on each side of the intestine, between it and the tuberosity of the 

 ischium : this is called the ischio-rectal fossa. 



The ischio-rectal region presents in the middle line the aperture of the anus : 

 around this orifice the integument is thrown into numerous folds, which are 

 obliterated on distension of the intestine. The integument is of a dark color, 

 continuous with the mucous membrane of the rectum, and provided with numerous 

 follicles, which occasionally inflame and suppurate, and may be mistaken for 

 fistulse. The veins around the margin of the anus are occasionally much dilated, 

 forming a number of hard pendent masses, of a dark bluish color, covered partly 

 by mucous membrane and partly by the integument. These tumors constitute the 

 disease called external piles. 



Dissection (Fig. 590). Make an incision through the integument, along the median 

 line, from the base of the scrotum to the anterior extremity of the anus: carry it round the 

 margins of this aperture to its posterior extremity, and continue it backward to about an inch 

 behind the tip of the coccyx. A transverse incision should now be carried across the base of 

 the scrotum, joining the anterior extremity of the preceding ; a second, carried in the same 

 direction, should be made in front of the anus ; and a third at the posterior extremity of the 

 first incision. These incisions should be sufficiently extensive to enable the dissector to raise the 

 integument from the inner side of the thighs. The flaps of skin corresponding to the ischio- 

 rectal region should now be removed. In dissecting the integument from this region great care 

 is required, otherwise the Corrugator cutis ani and External sphincter will be removed, as they 

 are intimately adherent to the skin. 



The superficial fascia is exposed on the removal of the skin : it is very thick, 

 areolar in texture, and contains much fat in its meshes. In it are found ramifying 

 two or three branches of the perforating cutaneous nerve ; these turn round the 

 inferior border of the Gluteus maximus. and are distributed to the integument 

 around the anus. 



In this region, and connected with the lower end of the rectum, are four 



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