MALE PERINEUM 347 



interims muscle, and this again is covered by the parietal or 

 obturator layer of the pelvic fascia which is continued down 

 to be attached to the tuberosity of the ischium and the 

 ligamentum sacro-tuberosum. On the other hand, the anal 

 canal is clothed latero-medially by (i) the anal fascia or 

 inferior fascia of the pelvic diaphragm, a thin aponeurotic 

 membrane which invests the lateral surface of the levator ani ; 

 (2) by the levator ani muscle ; and (3) by the rectal portion 

 of the upper fascia of the pelvic diaphragm (O.T. visceral layer 

 of the pelvic fascia) a thin layer of fascia which covers that 

 part of the medial surface of the levator ani which is applied 

 to the anal part of the rectum (Fig. 130). Strictly speaking, 

 therefore, the perpendicular lateral or ischial wall of the 

 fossa is formed by the parietal layer of the pelvic fascia, 

 and the sloping medial or rectal wall by the anal fascia. 

 Anteriorly, the space is limited by the fascia of the urogenital 

 diaphragm (O.T. triangular ligament) whilst posteriorly, it is 

 bounded by the posterior or distal margin of the glutaeus 

 maximus and the ligamentum sacro-tuberosum. 



Contents. The ischio-rectal fossa is completely filled up 

 by a mass of fat which is prolonged upwards into it from the 

 superficial fascia. The soft, pliable nature of this fat readily 

 allows of the distension of the anal canal. Embedded in its 

 midst are certain blood-vessels and nerves. Crossing the fossa 

 from its lateral to its medial wall are the inferior hcBmorrhoidal 

 vessels and nerve ; entering the fossa at its posterior part is the 

 perineal branch of the fourth sacral nerve ; turning round the 

 distal border of the glutaeus maximus, not far from the coccyx, 

 is the perforating cutaneous branch of the second and third 

 sacral nerves ; whilst in the anterior part of the space will 

 be found the scrotal branches of the perineal nerve (Fig. 129). 



Dissection. Begin by exposing the margin of the glutceus maximus 

 muscle. Take a point a short distance to the lateral side of the tuber 

 ischiadicum and another in the middle line about an inch above the tip of 

 the coccyx, and cut boldly down through the superficial fascia, in a line 

 between these points, until the fleshy fibres become visible. Winding 

 round the margin of the muscle, so as to gain its superficial aspect, 

 there are a few small arteries and nerves. The arteries are derived from 

 the inferior hcemorrhoidal vessels, or from the inferior ghiteal artery, whilst 

 the nerves are the perforating cutaneous branch from the second and third 

 sacral nerves and some offsets from the posterior cutaneous nerve of the 

 thigh. All are destined for the supply of the skin on the distal part of 

 the gluteal region. The perforating cutaneous nerve turns round the 

 margin of the gluteus maximus close to the coccyx, whilst the cutaneous 

 branches from the posterior cutaneous nerve of the thigh appear on the 



