MALE PERINEUM 159 



obturator fascia, which clothes the medial surface of the 

 obturator internus. At the apex cw roof the obturator fascia 

 blends with the inferior fascia of the pelvic diaphragm. The 

 anterior boundary is the base of the fascia of the urogenital 

 diaphragm and the transversus perinei muscle which runs 

 along its superficial aspect. The posterior boundary is formed 

 by the inferior borders of the sacro-tuberous ligament and the 

 glutaeus maximus muscle. The inferior boundary is the tough 

 integument of the posterior part of the perineum. 



The fossa is widest and deepest posteriorly, and narrowest 

 and most shallow in front, where it is prolonged forwards, 

 above the base of the fascia of the urogenital diaphragm. 



In its lateral wall, in a canal in the obturator fascia, 1 

 35-40 mm. above the lower margin of the ischial tuberosity, lie 

 the internal pudendal artery and its venae comites with the 

 perineal nerve below them and the dorsal nerve of the penis 

 above them. The inferior haemorrhoidal branch of the 

 pudendal nerve and the accompanying inferior haemorrhoidal 

 branch of the internal pudendal artery pierce the fascia of 

 the lateral wall posteriorly, and the superficial and deep 

 terminal branches of the perineal branch of the pudendal 

 nerve and the perineal and transverse perineal branches of 

 the internal pudendal artery pierce it anteriorly. The perineal 

 branch of the fourth sacral nerve pierces the lower part of 

 the coccygeus muscle in the medial wall. 



The contents of the fossa are: (i) An elastic pad of fat, 

 which fills the cavity. (2) The inferior haemorrhoidal vessels 

 and nerves which traverse the fat on their way from the 

 postero-lateral angle to the medial wall of the fossa. (3) 

 Portions of the posterior scrotal (labial) branches of the 

 superficial division of the perineal nerve. (4) The deep 

 division of the perineal' nerve. (5) The perineal and trans- 

 verse perineal arteries, in the anterior angle. (6) The perineal 

 branch of the fourth sacral nerve is at the postero-medial angle. 

 (7) Turning round the inferior border of the glutaeus maximus, 

 between the coccyx and the ischium, the perforating cutaneous 

 branch from the second and third sacral nerves. 



The fat which fills the fossa acts as an elastic pad which 

 allows the anal passage to expand as the faeces are expelled 

 through it, and assists it in closing the canal after the faeces 

 have passed. 



1 O.T. Alcock's canal. 



