PELVIS MINOR 485 



of the parietal layer. In the space between the two lines of 

 attachment, on each side, the anterior fibres of the correspond- 

 ing levator ani arise from the back of the body of the pubis. 



The dissector should now turn to the perineum and 

 examine the pelvic fascia from below. He has already seen 

 that it forms the lateral wall of the ischio-rectal fossa and 

 is carried medially from the margin of the pubic arch, as 

 the superior fascia of the urogenital diaphragm, to the median 

 plane, where it turns backwards along the urethra and round 

 the anterior border of the levator ani. 



He has seen also that the levator ani arises from the 

 parietal fascia of the lateral wall of the ischio-rectal fossa 

 and passes downwards and medially to the wall of the 

 anal canal, into which many of its fibres are inserted. The 

 levator ani must now be divided from before backwards, 

 midway between its origin and its insertion, and the upper 

 portion must be turned towards the pelvic wall. When 

 that has been done, the lower surface of the superior fascia 

 of the pelvic diaphragm will be exposed, and the dissector 

 will see, after the removal of the peritoneum and extra- 

 peritoneal fat above, and the levator ani below, that now the 

 visceral fascia alone separates the pelvic cavity above from 

 the perineum below, and he can convince himself that the 

 visceral layer springs from the parietal layer immediately 

 above the origin of the levator ani, and that, as it runs 

 towards the median plane, it encloses the pelvic viscera. He 

 will find also, if he traces the inferior surface of the visceral 

 layer forwards, that it blends anteriorly, round the anterior 

 border of the levator ani, with the upper fascia of the uro- 

 genital diaphragm, which is formed by the parietal layer of 

 the pelvic fascia. He has still to demonstrate the cleavage of 

 the visceral layer into secondary lamellae which ensheathe the 

 pelvic viscera. To do this he must take the following steps : 



Dissection. Detach the crura of the clitoris from the margins 

 of the pubic arch and trace the dorsal vein of the clitoris beneath 

 the arcuate ligament. Divide the dorsal vein and turn the 

 clitoris down. Separate the inferior fascia of the urogenital 

 diaphragm from the margin of the pubic arch on each side, if 

 that has not already been done during the dissection of the 

 perineum. Examine the sphincter urethrae membranaceae, 

 which lies above the inferior fascia of the urogenital diaphragm. 

 Divide the sphincter urethras membranaceae on each side and 

 turn it towards the median plane. Pass a probe into the urethra 

 and note that the anterior fibres of the sphincter pass in front 

 ii 31 a 



