238 



DISSECTION OF THE PERINEUM. 



and their 



general 



position. 



Dissection 



of external 



sphincter 



muscle. 



Difference 

 in cleaning 

 the ischio- 

 rectal fossa>. 



Dissection 

 of left 

 ischio-rectal 

 fossa. 



On right 

 side, seek 

 vessels and 

 nerves. 



Situation ; 



on the anus. The gut does not occupy, however, the whole of the I; 

 interval between the pelvic bones ; for on each side is a space, the I] 

 ischio-rectal fossa, in which is contained much loose fat, with the! 

 vessels arid nerves for the supply of the end of the gut. 



Dissection (fig. 91, p. 239 and fig. 92, p. 241). The workers on the | 

 two sides should dissect in conjunction displaying the muscles on thef 

 one side and the nerves and vessels on the other. The skin is to be 

 raised from this part of the perineum by the following cuts : One is 

 to be made across the perineum at the front of the anus, and is to 

 extend rather beyond the ischial tuberosity on each side. A second 

 is to be carried across in the same direction a little behind the tip of 

 the coccyx, and for the same distance. The two transverse cuts are to 

 be connected by carrying the knife along the mid-line, and around 

 the anus. The flaps of the skin thus marked out are to be raised 

 and thrown outwards from the middle line : in detaching the skin 

 from the margin of the anus, the superficial fibres of the sphincter 

 muscle may be injured if care be not taken, for they are close to 

 the skin without the intervention of fat. The dissector should trace 

 the external sphincter backwards to the coccyx, and forwards for u 

 short distance beneath the skin, and define a fleshy slip on each side 

 in front and behind to the subcutaneous fatty layer. 



The next step is to bring into view the ischio-rectal hollow 

 between the side of the rectum and the tuberosity of the hip-bone. 

 On the left side the fat is to be cleaned out of it without reference to 

 the vessels and nerves, but on the opposite side a special dissection is 

 to be made of them (fig. 92). To take out the fat from the left fossa, 

 begin at the outer margin of the sphincter ani, and proceed forwards 

 and backwards. In front the dissection should not extend farther 

 than a finger's breadth in front of the anus, while behind it should 

 lay bare the margin of the glutens maximus. On the inner side of 

 the hollow the levator ani (sometimes very pale) is to be exposed by 

 the removal of a thin layer of areolar tissue (anal fascia). On the 

 outer boundary the pudic vessels and the accompanying nerves 

 should be denuded : they lie in a canal formed by fascia, and at some 

 distance from the surface. 



On the right side it is not necessary to clean the muscular fibres 

 when following the vessels and nerves. If the student begins at the 

 outer border of the sphincter, he will find the inferior heeraorrhoidal 

 vessels and nerve, which he may trace outwards to the pudic trunks ; 

 some of the branches, which join the superficial perinea! and interior 

 pudendal nerves, are to be followed forwards. In the posterior angle 

 of the space seek a small offset of the fourth sacral nerve , and 

 external to it, branches of the perforating cutaneous nerve from the 

 sacral plexus, with small vessels, turning round the border of the 

 glutens. Near the front of the fossa is the superficial perinea! artery 

 with a nerve ; and the last, alter communicating with the hsemor- 

 rhoidal nerve, leaves the fossa. A second perinea! nerve, with a deeper 

 position, may be found at the front of the hollow. 



The ISCHIO-RECTAL FOSSA (fig. 91) is the interval between the 



