chap, xviii.] THE PERINEUM, 349 



(the three long scrotal nerves) are included within 

 the space. 



The triangular ligament has a depth of about 

 one and a half inches in the middle line, and is formed 

 of two layers, of which the posterior is derived from 

 the pelvic fascia. The membranous urethra, surrounded 

 by the compressor urethrae, lies between the two layers, 

 and runs about one inch below the symphysis, and 

 about three-quarters of an inch above the central point 

 of the perineum. The artery to the bulb passes in- 

 wards between the two layers about half an inch above 

 the base of the ligament and one inch and a-half in 

 front of the anus. The dorsal vein and the terminal 

 part of the pudic artery and nerve pierce the anterior 

 layer of the ligament about half an inch below the 

 symphysis. In uncomplicated rupture of the mem- 

 branous urethra, the urine extravasated would be 

 limited to the space beween the layers of the ligament, 

 until subsequent suppuration had made a way for it to 

 escape. When extravasation occurs behind the trian- 

 gular ligament, the effusion barely escapes the pelvic 

 cavity, and usually by following the rectum gains the 

 anal part of the perineum. 



Just beyond the triangular ligament is the pro- 

 state, surrounded by its capsule, and the prostatic 

 venous plexus. In dissecting down from the surface 

 to the prostate, we meet, as Cunningham has well 

 pointed out, alternate strata of fascial and muscular 

 tissue, forming seven layers in all, viz. : (1) Superficial 

 fascia ; (2) superficial perineal muscles ; (3) triangular 

 ligament (ant. layer) ; (4) compressor urethrse imiscle ; 

 (5) triangular ligament (post, layer) ; (6) levator ani 

 'muscle ; (7) capsule of prostate. 



Lateral lithotomy.- The first incision is from 

 two to three inches in length, is commenced just to 

 the left of the middle line and just behind the central 

 point of the perineum, i.e., about one and a quarter 



