

MALE PERINEUM 157 



It is covered on each side by the levatores ani and coccygei 

 muscles and their fasciae; but^he canal and the muscles 

 which cover it occupy only the middle part of the triangle, 

 and on each side between the muscles covering the canal 

 and the lateral boundary of the triangle lies an ischio-rectal 

 fossa. The fossa is bounded, medially by the levator ani 

 and the coccygeus, laterally by the ischium covered by the 

 obturator internus and the obturator fascia, posteriorly by 

 the inferior borders of the glutaeus maximus and the sacro- 

 tuberous ligament, and anteriorly by the base of the fascia of 

 the urogenital diaphragm blended with the posterior border 

 of the fascia of Colles. Each ischio-rectal fossa is filled with 

 a pad of soft elastic fat in which lie the inferior haemorrhoidal 

 vessels, accompanied by the inferior haemorrhoidal nerve, 

 the perineal branch of the fourth sacral nerve, portions of 

 the superficial and deep branches of the perineal nerve and 

 the accompanying rami of the perineal branch of the pudendal 

 artery. All the structures mentioned must now be displayed. 



Dissection. Begin, on each side, by exposing the inferior 

 margin of the glutaeus maximus muscle, which forms one of the 

 posterior boundaries of the fossa. Take a point a short distance 

 to the lateral side of the ischial tuberosity and another in the 

 median plane about an inch above the tip of the coccyx, and cut 

 boldly down through the superficial fascia, in a line between 

 those points, until the deep fascia covering the fleshy fibres 

 becomes 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 hcemor- 

 rhoidal vessels, or from the inferior glutcal 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 over 

 the inferior part of the gluteal region. The perforating cutaneous 

 nerve turns round the margin of the glutaeus maximus near the 

 coccyx, whilst the gluteal branches from the posterior cutaneous 

 nerve of the thigh appear on the lateral side of the tuber ischia- 

 dicum. When the vessels and nerves mentioned have been 

 secured, clean the lower border of the glutaeus maximus, then 

 push the fat in the fossa in front of it forwards, pull the muscle 

 backwards and expose and clean the lower border of the sacro- 

 tuberous ligament, which lies under cover of the muscle. After 

 the margin of the sacro-tuberous ligament has been defined, 

 detach the fat from the lateral wall of the fossa, partly with the 

 aid of the blade and partly with the aid of the handle of the 

 scalpel, and push it forwards and medially, but be careful not 

 to injure any vessels or nerves. When the fat has been detached 

 from the posterior and lateral walls of the fossae carry the knife 

 obliquely forwards and medially in the fat, from the angle 

 between the glutaeus maximus and the ischial tuberosity towards 



