628 ABDOMEN 



attachment on each side the anterior fibres of the 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 uro-genital diaphragm, to the medial 

 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 laterally towards the pelvic wall. When 

 this 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 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 immediately above 

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

 the medial plane, it encloses the pelvic viscera. He will 

 also find, if he traces the under 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 uro-genital 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 urethrse membranaceae which lies 

 above the inferior layer of the uro-genital diaphragm. Divide the sphincter 

 urethra 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 of the urethra, and that its posterior fibres pass over the wall 

 of the vagina. Behind the sphincter urethroe membranaceae lies the 



