440 



THE MUSCULATURE 



The outlet of the pelvis thus bounded by bone, ligaments and by muscles be- 

 longing to the lower extremity presents two triangles (figs. 392, 394), an anterior or 

 urogenital triangle, with the base between the two ischial tuberosities and the apex 

 below the symphysis pubis, and a posterior or rectal with the base between the 

 ischial tuberosities and the apex at the coccyx which projects into it here. The 

 outlet is closed b}^ a special musculature divisible into three groups of muscles and 

 fascia; those of the pelvic diaphragm and anus, those of the urogenital diaphragm, 

 and those of the external genitalia. 



The pelvic diaphragm [diaphragma pelvis] extends from the upper part of the 

 pelvic surface of the pubis and ischium to the rectum which passes through it to be 

 surrounded by the external sphincter. The urogenital trigone or urogenital dia- 

 phragm [diaphragma urogenitale] lies between the ischio-pubic rami superficial to 

 the pelvic diaphragm and surrounds the membranous urethra and in the female 

 also the vagina. The external genital muscles lie superficial to the trigone. 



The muscles of the pelvic diaphragm are two in number on each side, the coccy- 

 geus, and the levator ani (figs. 395, 396, 397). The coccygeus arises from the 



Fig. 395. — The Pelvic Diaphragm in the Female, from below and behind. 



<\^ 



Coccygeus 



Ano-coccy- 

 geal raphe 



_Ilio-coccy- 

 geus 



Pubo-coccy- 



geus 

 Pre-anal 



fibres of the 



pubo- 



coccygeus 



Arcus tendineusof levator ani 



Anus 



Vagina 



Urethra 



ischial spine and is inserted into the lateral margin of the lower sacral and the 

 upper coccygeal vertebrae. It is closely applied to the pelvic surface of the sacro- 

 spinous (small sciatic) ligament. In so far as it is active it flexes and abducts the 

 coccyx. 



The levator ani arises (figs. 395, 396, 397) from the inner side of the pubis, 

 along a line extending laterally from the inferior margin of the symphysis to the 

 obturator canal, and from the obturator fascia along a line, the arcus tendineus, 

 extending from the pubis to the spine of the isciliium. The levator ani is inserted 

 into the median rai)hc back of the anus, the ano-coccygeal raphe, into the tip and 

 sides of the coccyx and into an aponeurosis, which is attached to the anterior 

 sacrococcygeal ligament. It is divisible into three portions, a pubo-coccygeal, an 

 iliococcygeal, and a puho-rectal. The levator ani muscles of the two sides are sepa- 

 rated by a slit which extends from the rectum to the symphysis pubis and in which 

 in the male lie the lower part of the prostate, anfl tlie membranous urethra (fig. 

 396), and in tlie female the vagina and urethra (fig. 395). Back of the rectum 

 some of the fibre-bundles from the muscles of the two sides interdigitate, while 



