

THE MALE PERINEUM. 209 



pudic vessels and nerve can be easily felt, grooving the 

 inner aspect of the tuber osity of the ischium. 



In the external incision for lateral lithotomy the knife 

 sinks into the ischio-rectal fossa, and will divide the 

 superficial hsemorrhoidal vessels and nerves. Abscesses 

 have a great partiality for the ischio-rectal fossae, and 

 often burrow to a most remarkable extent. A fistula in 

 ana, is the sinus left on the contraction of the cavity of 

 such an abscess. True fistulse exist external to the 

 sphincter, and always extend as far up as its upper 

 border. They are called complete or incomplete accord- 

 ing as their openings are situated ; thus, in the former 

 case, one opening is in the rectum and the other on the 

 surface of the body, generally near the anus; in the 

 latter, there is an opening into the bowel and none ex- 

 ternal, or the converse. 



The operation for its cure consists in passing a knife 

 through the fistulous track into the bowel, and cutting 

 through all the tissues between the edge of the knife and 

 the interior of the gut. These tissues are the pseudo- 

 mucous membrane of the fistula, the external sphincter, 

 some few fibres of the levator ani, the branches of the 

 inferior hsemorrhoidal vessels and nerves, the internal 

 sphincter, and the mucous membrane of the inner bowel 

 and its vessels. 



Deep Dissection of the Perineum. Those structures be- 

 fore described as lying beneath the anterior layer of the 

 triangular ligament may be now removed, when its pos- 

 terior layer will come into view. This is derived from 

 the pelvic fascia, and covers the hinder part of the mem- 

 branous urethra, and outer surface of the prostate gland ; 

 it is attached below to the anterior layer, forming a 



