344 SURGICAL APPLIED ANATOMY. [Chap. xviu. 



membraoie. The ob.toratpr a^ter^ is an exception to this 

 rule, since it parses 'over the upper border of the 

 paiietal pelvic fascia (Cunningham). The nerves in 

 ike pelvis lie behind or oiitsyie ohp^fa^oia, and, there- 

 fore, the pelvic ve-^els. and, ih^ pelvic nerves are, 

 excepting the obturator, separated from one another 

 by this layer of tissue. 



The male perineum. The perineum is a 

 lozenge-shaped space bounded by the symphysis, the 

 rami of the pubes and ischia, the ischial tuber osities, 

 the great sacro-sciatic ligaments, the edges of the two 

 great gluteal muscles, and the coccyx. A transverse 

 line drawn across the space between the anterior ex- 

 tremities of the tubera ischii, and just in front of 

 the anus, divides the perineum into two parts. The 

 anterior part forms nearly an equilateral triangle, 

 measuring about three and a quarter inches on all 

 sides. It is called the urethral triangle. The posterior 

 part is also somewhat triangular, contains the rectum 

 and ischio-rectal fossa, and is called the anal triangle. 

 The whole space measures about three and a half inches 

 from side to side, and about four inches from before 

 backwards in the middle line. The average antero- 

 posterior diameter of the pelvic outlet in the male 

 averages three and a quarter inches. This measure- 

 ment in the undissected subject is increased to four 

 inches by the curving of the surface. The average 

 transverse diameter of the male pelvic outlet is three 

 and a half inches, and corresponds to the measurement 

 of the perineum above given. 



The bony framework of the perineum can be felt 

 more or less distinctly all round, and in thin subjects 

 the great sacro-sciatic ligaments can be made out 

 beneath the great gluteal muscle. The anus is in the 

 middle line between the tubera ischii, its centre being 

 about one and a half inches from the tip of the 

 coccyx. The rop/je, a central mark or ridge in the 



