THE PELVIC AND PERINEAL MUSCLES. 559 



becomes continuous with the iliac fascia. It descends over the surface of the pyri- 

 formis and laterally over the upper portion of the obturator internus and the pelvic 

 surface of the pelvic diaphragm. In the upper part of its course over the pelvic dia- 

 phragm it is crossed by a curved thickening, the arcus tendineus, which is attached 

 behind to the spine of the ischium and passes in front upon the sides of the prostate 

 gland or, in the female, upon the bladder, and is continued thence to the anterior 

 pelvic wall to be attached on either side of the symphysis pubis, a little above its 

 lower border, as a lateral pubo-prostatic (^piibo-vesical) ligame?it. Along this tendi- 

 nous arch the pelvic fascia gives of? a layer which passes inward to the pelvic viscera, 

 and is termed the fascia endopelvina. In its anterior portion this forms an investment 

 of the prostate in the male and of the base of the bladder in the female, and its under 

 surface in this region is in contact with, and indeed may be regarded as being fused 

 with, the superior layer of the triangular ligament (page 563). That portion of the 

 layer which intervenes between the prostate (or bladder) and the posterior surface 

 of the body of the pubis forms what is termed the median pubo-prostatic {^pubo -vesical ) 

 ligament. 



The continuation of the pelvic fascia passes downward over the surface of the 

 pelvic diaphragm, and is termed the superior fascia of that structure (fascia dia- 

 phragmatis pelvis superior). 



The Obturator Fascia. — From the line along which the pelvic fascia leaves the 

 surface of the obturator internus muscle to pass upon the pelvic diaphragm a sheet of 

 fascia is continued downward over the surface of the obturator internus muscle to be 

 attached below to the tuberosity and ramus of the ischium and the ramus inferior of 

 the pubis. This is the obturator fascia. 



Along its upper border, nearly corresponding with the arcus tendineus of the 

 pelvic fascia, but lying above this thickening and ending anteriorly farther from the 

 median line, is a similar curved thickening extending from the spine ot the ischium, 

 or in some cases from the ilio-pectineal line behind to the posterior surface of the 

 body of the os pubis in front. From this thickening the greater portion of the levator 

 ani muscle arises ; it is consequently termed the arcus tendineus m. levatoris ani, or 

 more briefly the white line. From the line a thin layer of fascia is continued inward 

 upon the under surface of the levator ani, forming what is termed the anal fascia 

 (fascia diaphragmatis pelvis inferior). 



This latter fascia forms the inner and the obturator fascia the outer wall of the 

 ischio-rectal fossa. Near its lower border the obturator fascia splits into two layers to 

 form a canal, the canal of Alcock, along which the pudic vessels and nerve pass 

 towards the perineum. 



In the above description the term pelvic fascia is applied to the layer of fascia which lines 

 the entire true pelvic cavity, — that is to say, the funnel-shaped cavity included between the pel- 

 vic brim and floor. This conception, employed by the German authors, differs somewhat from 

 that usually held by English anatomists, in that the latter restrict the term to that portion of 

 the fascia 'extendina: from the ilio-pectineal line to the white line, the continuation down- 

 ward over the pelvic diaphragm bemg termed the recto-vesical fascia, from which extensions 

 pass to the bladder, prostate gland, and rectum. The term recto-vesical has also been restricted 

 to the portion of the sheet which extends between the rectum and the bladder and encloses the 

 seminal vesicles (Cunningham), and if the term is to be employed at all, this application of it 

 seems to be the preferable one. 



Confusion has also existed in the application of the term "white line," since it has been 

 made to include both the arcus tendineus proper and the thickened band from which the leva- 

 tor ani takes its origin {arcus tendineus m. levatoris ani). These two bands are, however, quite 

 distinct, especially anteriorly, as a careful inspection of the subject will demonstrate, and it seems 

 preferable to restrict the term "white line" to that from which the levator ani arises, naming 

 that at which the fascia endopelvina begins the arcus tendineus. 



{a) THE PELVIC MUSCLES. 



I. -Levator ani. 2. Coccygeus. * 



3. Pyriformis. 



The floor of the pelvis is formed by two muscles which constitute an almost 

 complete partition, the pelvic diaphragm, separating the pelvic from the perineal 

 region. The more anterior and larger of these muscles is the levator ani, the coccy- 



