ARRANGEMENT OF THE FASCIA OF THE PELVIS. 129 



been modified to effect the more efficient closure of the pelvic 

 outlet, and to support the superimposed viscera, marked 

 differences in the disposition of the fascise fjxist, and are 

 intimately associated with changes in the attachment of the 

 muscles, whilst they are probably also dependent, at least to 

 some extent, on functional changes. 



As is well known, both the upper and lower surfaces of the 

 levator ani in man are covered by thin layers of fibrous tissue 

 closely adherent to the subjacent muscle. They correspond to 

 the two layers of fascia investing the flexor group of tail muscles 

 in carnivores, and they exhibit distinctive features in different 

 parts of the pelvic floor. Posteriorly, the upper layers of the 

 two sides are continuous behind the rectum, and fuse with the 

 ligamenta sacro-coccygei auteriora (tendinous insertion of the 

 pubo-coccygei). In the region of the canal through which the 

 rectum passes, they descend in contact with the rectal wall, and 

 appear to end over the external sphincter ani, whilst at the 

 front part of the pelvic floor the fascial layer of each side turns 

 round the free inner edge of the pubo-coccygeus and becomes 

 continuous with the layer on its under surface, in the same way, 

 indeed, as already described in other mammals. 



The lower fascia of the levator ani also presents a different 

 disposition behind and in front. Posteriorly, where it covers 

 the ilio-coccygeus, it forms a thin membranous layer — the anal 

 fascia — ■which joins with the corresponding fascia of the opposite 

 side in the ano-coccygeal raphe. ' In the region of the canal for 

 the rectum it appears to end, like the upper layer, over the 

 external sphincter, and according to HoU,^ is finally lost in the 

 subcutaneous fatty tissue in the region of the anus. In front 

 of the pre-anal fibres of the pubo-coccygeus, however, the fascia 

 is continuous round the inner margin of the pubo-coccygeus w^ith 

 the upper fascia of the muscle, and externally passes to be 

 attached to the descending ramus of the pubis and the ascending 

 ramus of the ischium. Between its external bony attachment and 

 the inner border of the pubo-coccygeus, it lies in relation to the 

 posterior surface of the sphincter of the membranous urethra 

 and the transversus perinei profundus, thus forming the posterior 

 layer of the triangular ligament. 



^ Loc. c'd. 



