346 SURGICAL APPLIED ANATOMY. [Chap. xvm. 



the perineum, is the central point of the perineum. 

 The two transverse perineal muscles, the accelerator 

 urinse, and the sphincter ani meet at this point, which 

 also corresponds to the centre of the inferior edge of 

 the triangular ligament. The bulb is just in front of 

 it, as is also the artery to the bulb, and in lithotomy, 

 therefore, the incision should never commence in 

 front of this spot. 



The perineal space is separated from the pelvic 

 cavity by the levator ani muscles and recto-vesical 

 fascia, as already mentioned. The depth of the perineum 

 means the distance between the skin and the pelvic 

 floor. This depth depends, to a great extent, upon the 

 amount of fat under the integument. It varies 

 considerably in different parts, measuring from two to 

 three inches in the hinder and outer parts of the 

 perineum, and less than one inch in the anterior parts 

 of the space. 



The iscMo-rectal fossa is of pyramidal shape, 

 its apex being at the white line, and its base being 

 formed by the skin between the anus and the ischial 

 tuberosities. It measures about two inches from be- 

 fore back, one inch from side to side, and is between 

 two and three inches in depth. Its boundaries are: on 

 the outer side, the obturator interims muscle covered 

 by the parietal layer of the pelvic fascia; on the inner 

 side, the levator ani, covered by the anal fascia ; in 

 front, the base of the triangular ligament and the 

 trans versus perinei muscle ; and behind, the gluteus 

 maximus, great sacro-sciatic ligament, and coccygeus. 

 The pudic vessels and nerves are on the outer wall, 

 embedded in the fascia over the obturator muscle, and 

 are placed about one and a half inches above the lower 

 border of the tubera ischii. 



The part of the rectum which occupies the space 

 between the two fossae is supported by the levatores 

 ani, external sphincter, and recto-vesical fascia. Its 



