PELVIC FASCIA. 489 



the pubic ramus, and is inserted into a median raphe on the dorsum of the membranous 

 urethra. This muscle is homologous with the compressor venae dorsalis penis of lower 

 animals. 



The sphincter urethrse in the female is smaller than in the male. Its 

 insertion is modified by the relations of the urethra to the vagina. The anterior 

 fibres are continuous with those of the opposite side above the urethra ; the 

 intermediate fibres pass between the urethra and vagina, and the posterior fibres 

 are attached, along with the transversus perinei profundus (transversus vaginae), into 

 the side of the vagina. 



Nerve-Supply. Deep branch of the perineal nerve (pudendal, S. 3. 4.). 



Action. It is a feeble compressor of the membranous urethra, and by no means a sphincter. 

 In the female it has an accessory influence in constricting the vagina. 



THE FASCIAE OF THE PELVIS. 



The extra-peritoneal tissue in the pelvic cavity is of great importance. The 

 hypogastric vessels and their branches, the visceral nerves and plexuses, the 

 ureters, and ductus deferentes, take their course in this tissue outside the peri- 

 toneum. It forms in relation to the rectum a thick sheath, for the most part 

 devoid of fat, which encloses the lower part of the rectum completely, down to its 

 termination in the anal canal. It forms a kind of packing for the parts of the 

 bladder uncovered by peritoneum, and is present under the organ in relation to the 

 symphysis pubis and pubo-prostatic ligaments. In the female it forms, in addition, 

 the basis or matrix of the broad ligament, and also occurs as a layer devoid of fat, 

 which loosely connects the anterior surface of the cervix uteri with the base of the 

 bladder. 



FASCIA PELVINA. 



The cavity of the pelvis minor, in the erect position, resembles a basin tilted 

 forward, with its margin formed by the superior aperture of the pelvis, with a 

 cylindrical wall, and a concave floor, formed by bones, ligaments, and muscles. 

 The deficiencies in the bony walls of the cavity are filled up laterally by the 

 obturator membrane and the sacro- tuberous and sacro-spinous ligaments. Tn- 

 feriorly and anteriorly, behind the symphysis pubis, the fascia diaphragmatis 

 urogenitalis inferior fills up the pubic arch, and separates the anterior part of the 

 pelvic cavity from the perineum. The inner surface of this osseo-ligamentous 

 chamber is lined by a series of muscles ; the piriformis and coccygeus posteriorly, 

 the obturator internus on each side, and the sphincter urethras membranacese and 

 transversus perinei profundus, inferiorly and anteriorly, on the pelvic surface of 

 the inferior fascia of the urogenital diaphragm. 



The pelvic fascia, continuous above with the fascial lining of the abdominal 

 cavity, forms a continuous cylindrical investment for these muscles. On the pelvic 

 surface of the pubis, where muscles are absent, it is merged with the periosteum, 

 [t gains an attachment to the spine of the ischium as that projects between the 

 piriformis and obturator internus muscles. Perforations occur in it for the trans- 

 mission of the obturator nerve and the parietal branches of the hypogastric 

 artery. At the inferior aperture of the pelvis, it is attached to the posterior 

 border or base of the fascia inferior of the urogenital diaphragm, to the ischial 

 ramus and tuberosity, and to the lower edge of the sacro-tuberous ligament. 

 Different names are applied to the fascia in relation to the several muscles which 

 ; covers. Posteriorly it constitutes the piriformis fascia: laterally it is the 

 obturator fascia, while that part of the sheet of fascia which covers the pelvic 

 surface of the sphincter urethras membranacese and transversus perinei profundus 

 known as the fascia diaphragmatis urogenitalis superior. 



The disposition of the pelvic fascia is complicated by its relations to (1) the 

 structures which constitute the pelvic floor, and (2) the genito-urinary passages 

 and the rectum. 



