502 DISSECTION OF THE PELVIS. 



be inserted after the following manner : The anterior, the longest, descend 

 by the side of the prostate and join, in front of the rectum, with the mus- 

 cle of the opposite side in the central point of the perinseum ; the middle 

 fibres blend with the side of the rectum ; whilst the posterior meet the 

 opposite muscle behind the gut, and are attached in part to the side of the 

 coccyx (p. 390). 



The anterior fibres of the levator are in contact with the triangular 

 perineal ligament; 1 and there is an interval between the two muscles, 

 which allows the urethra, with the vagina in the female, to pass from the 

 pelvis. The posterior border is parallel to the coccygeus muscle. The 

 upper surface is contiguous to the recto-vesical fascia ; and the under sur- 

 face looks to the perinaHim (ischio-rectal fossa). The two muscles, by 

 their union, form a fleshy layer or diaphragm across the outlet of the pel- 

 vis, similar to that which separates the abdomen from the chest ; this par- 

 tition is convex below and concave above, and gives passage to the rec- 

 tum. 



Action. By the union of the muscles of opposite sides below the urethra 

 this tube can be raised, and compressed during their contraction. Whilst 

 the urine is flowing the fibres are passive, but towards the end of micturi- 

 tion they contract suddenly, and help the other muscles in clearing the 

 passage. 



As the levatores descend by the side of the vesiculse seminales, and the 

 prostate, they will compress and evacuate the contents of those viscera. 



The hindmost fibres, which are fixed to the coccyx, will assist the coc- 

 cygeus in moving forwards that bone. 



Dissection. The recto-vesical fascia will be seen by detaching the fleshy 

 fibres of the levator ani and the coccygeus at their origin, and throwing 

 both downwards. The thin membrane descends on the levator ani to the 

 side of the bladder and the rectum, and sends downwards sheaths around 

 the prostate and the gut. To demonstrate those sheaths one incision is to 

 be made along the prostate, and another along the lower end of the rectum, 

 below the fascia ; and the tubes are to be isolated from the viscera. 



The recto-vesical fascia supports and partly invests the viscera of the 

 pelvis. Covering the pelvic surface of the levator ani it is fixed above, 

 like that muscle, to the wall of the pelvis in front and behind, and between 

 those attachments it joins the pelvic fascia. Below it meets the fascia of 

 the opposite side, yi the centre of the pelvis, and forms a partition across 

 the cavity, like that of the levatores ani, which is perforated by the blad- 

 der and the rectum. The partition is supported anteriorly by being fixed 

 to the pubes, and posteriorly, where it blends with the fascia on the cocy- 

 geus, by being inserted into the coccyx : it is concave above and convex 

 below, and divides the cavity of the pelvis from the perinaeal space. This 

 septal piece is attached to the viscera which pierce it, forming ligaments 

 for them ; and from the under surface tubes are prolonged on the rectum 

 and the prostate. 



The sheath on the rectum incloses the lower three inches of the intestine, 

 and gradually becomes very thin towards the anus ; between it and the 

 intestine are interposed the branches of the upper hemorrhoidal vessels, 

 with a layer of fat. 



1 The anterior part of the muscle which descends by the side of the prostate, and 

 unites with its fellow below the membranous part of the urethra, thus supporting 

 that canal as in a sling, is named sometimes levator sen compressor prostatce. 



