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The pelvic floor, tense in its anterior part and flexible posteriorly, is formed behind the symphysis pubis by, successively, (1) the fascia of the urogenital diaphragm and the transversus perinei profundus and sphincter muscle of the membranous urethra between them, the latter enclosing the urethra; and the vagina in the female. (2) The perineal body. (3) The levator ani and external sphincter of the anus on each side of the anal canal; (4) the ano-coccygeal body, between the anal canal and the coccyx, containing the main insertions of the levatores ani and external sphincter.
Median pubo-prostatic ligament
FIG. 434.-RELATIONS OF THE PELVIC FASCIA TO THE RECTUM AND PROSTATE.
The levator ani muscle completes the concave floor of the pelvic cavity, sweeping downwards and backwards from its lateral wall, so as to form a muscular diaphragm, with an intra-pelvic and a perineal surface. Its superior concave pelvic surface occupies the lateral part of the pelvic floor. Its inferior convex surface forms the oblique medial wall of the ischio-rectal fossathe, lateral wall of which is formed by the obturator fascia covering the pelvic surface of the obturator internus. In this wall is a fascial sheath containing the pudendal vessels and nerve. The levator ani is covered on both surfaces by pelvic fascia. The anal fascia clothing its perineal surface is thin and unimportant. The fascia covering its intra-pelvic surface is thick and strong. At the origin
of the muscle it is continuous with the general fascial lining of the pelvic cavity, and gives rise to a conspicuous thickening, the tendinous arch (arcus tendineus) of the pelvic fascia, which stretches like a bow-string from the back of the symphysis pubis to the ischial spine. This band is related not so much to the origin of the levator ani muscle, which often extends higher up external to the pelvic fascia, as to the attachments of the fascial investments of the genito-urinary passages, to be described below. There are sometimes additional thickenings of the fascia, branching upwards from the tendinous arch towards the superior aperture of the pelvis. At the insertion of the levator ani, the fascia clothing its pelvic surface is attached to the perineal body, the margin of the anal canal, and the ano-coccygeal body, over which it passes to be continuous, above the raphe of insertion of the levatores ani, with the layer of the opposite side. At the antero
FIG. 435.-RELATIONS OF PELVIC FASCIA TO THE RECTUM AND PROSTATE
inferior border of the muscle the fascia enclosing it become continuous with the superior fascia of the urogenital diaphragm; at its postero-superior border they join the fascia enclosing the coccygeus muscle.
Within the pelvic basin, the walls and floor of which are thus continuously invested by the pelvic fascia, are contained the rectum and bladder, and in the female the uterus, suspended and maintained in position by the peritoneum, extra-peritoneal tissue, and the pelvic vessels and nerves. They are essentially free to distend or collapse, and are not bound down by the pelvic fascia. The rectum in both sexes extends down to the floor of the pelvis, where the anal canal takes its origin. It is invested by the peritoneum and extra-peritoneal tissue, and occupies a special rectal channel; this is lined by pelvic fascia, which gains an attachment to the floor of the pelvis at the margin of the anal canal.
The arrangement of the fascia in relation to the genito-urinary passages is essentially different.
Just as from the perineal aspect the inferior aperture of the pelvis is divisible into two different parts,-a posterior or dorsal part, comprising the ischio-rectal
fossæ for the passage of the anal canal, and characterised by looseness and distensibility; and an anterior or ventral part,-the urethral triangle for the genitourinary passages, and characterised by firm fixation to the pubic bones; so also from the abdominal aspect it is found that, while in the posterior part of the pelvis a rectal channel exists, in which the rectum is free to collapse and distend, in the ventral part of the basin the genito-urinary passages are firmly fixed by means of
Recto-vaginal layer Lateral pubo-prostatic ligament
Bulb of the
Pubo-urethral fascia (pubo-vesical
Junction of rectum and anal canal
FIG. 436.-RELATIONS OF THE PELVIC FASCIA TO THE RECTUM, URETHRA, AND VAGINA (Median Section).
the pelvic fascia, which gives rise to a special suspensory ligament for the prostate gland and the prostatic urethra in the male, and for the urethra and vagina in the female.
A crescentic fold of pelvic fascia (suspensory ligament) arises in the neighbourhood of the sciatic spine from the general fascia covering the pelvic wall. It has a posterior free edge, through which the ductus deferens, vesical vessels, and nerves pass. Sweeping across the median plane, this border is continuous with the fold of the opposite side, the two together constituting the anterior limit of the rectal
channel. The fascial fold is composed of two layers, posterior and superior, between which is a large plexus of veins. They have separate attachments laterally to the general pelvic fascia. The posterior (recto-vesical) layer passes across the pelvis between the prostate gland and the rectum. Its inferior edge is attached to the perineal body between the base of the fascia of the urogenital diaphragm and the beginning of the anal canal. It forms a sheath for the vesiculæ seminales and ductus deferentes. This is rather in the form of a septum than a complete sheath; it effectually separates the vesiculæ seminales and the bladder from the rectum, forming the anterior wall of the rectal channel, but it allows the vesiculæ seminales to rest directly against the bladder. The superior layer extends forwards to the symphysis pubis. It has a lateral origin from the arcus tendineus in its whole length, and sweeping over the prostate gland, it is inserted along its line of junction with the bladder, and constitutes the so-called lig. puboprostaticum laterale (lateral true ligament of the bladder). It contains numerous bundles of muscular fibres in its anterior part, and forms a sheath for the passage of the inferior vesical vein along the lateral surface of the prostate gland. In front the fascia stretches from the back of the symphysis pubis, the arcuate ligament of the pelvis, and the superior fascia of the urogenital diaphragm to the neck of the bladder and the prostate gland, forming the lig. puboprostaticum medium. It is continuous across the median plane with the ligament of the opposite side. In the median line, where the two ligaments unite, a hollow occurs behind the symphysis pubis, known as the cavum Retzii. This ligament is composed of several layers separated by large veins (the pudendal plexus), which connect the inferior vesical vein with the dorsal vein of the penis and the hypogastric vein.
The sheath of the prostate gland (fascia prostata) is formed by (1) the superior fascia of the urogenital diaphragm on which it lies, (2) by the general pelvic fascia covering the intra-pelvic surfaces of the levatores ani on each side, and (3) it is completed above and behind by the two special layers of pelvic fascia just described. By these means the prostate gland and prostatic urethra are given a firm attachment to the anterior part of the pelvic walls and floor.
In the female an essentially similar arrangement of the pelvic fascia occurs in relation to the vagina and urethra. A crescentic fold of the fascia springs from the pelvic wall in the neighbourhood of the spina ischiadica, and sweeping medially to the lateral fornix of the vagina and in front of the rectum, separates into two layers, posterior and superior. Between the layers are numerous vessels, which, along with the visceral nerves, pierce its free edge. The posterior (recto-vaginal) layer passes medially behind the vagina, and gaining the median plane between the vagina and rectum, gives rise to the anterior wall of the rectal channel, and is attached below to the perineal body in the floor of the pelvis. The superior layer, taking origin from the arcus tendineus, is attached medially to the neck of the bladder, and constitutes the lateral pubo-vesical ligament. It is continuous in front with the anterior pubo-vesical ligament, which, as in the male, is divisible into several layers separated by veins. An intermediate (urethro-vaginal) layer of the fascia passes between and separates the urethra and vagina.
The urethra and vagina are by means of these layers of fascia firmly bound to the pelvic walls and floor, while the uterus and bladder are free to distend in the pelvic cavity.
MUSCLES OF THE PELVIS.
Diaphragma Pelvis.-The pelvic diaphragm is formed by the levator ani and coccygeus muscles, which serve to uphold the pelvic floor, and are related to the rectum and the prostate gland or vagina.
M. Levator Ani.-The levator ani arises from (1) the inferior part of the posterior surface of the body of the pubis, (2) the general pelvic fascia above or along the arcus tendineus, and (3) the pelvic surface of the spine of the ischium.
Its fibres are directed downwards and backwards, to be inserted into (1) the central point of the perineum (perineal body), (2) the external sphincter around
THE MUSCLES OF THE PERINEUM.
The perineal muscles are naturally separated into a superficial and a deep set by the fascia inferior of the urogenital diaphragm. Superficial to it are the sphincter ani externus, transversus perinei superficialis, bulbocavernosus, and ischiocavernosus; deep to it are the sphincter muscle of the membranous urethra and the transversus perinei profundus.
M. Sphincter Ani Externus.-This muscle is fusiform in outline, flattened, and obliquely placed around the anus and anal canal. It can be separated into three layers, subcutaneous, superficial, and deep. (1) The most superficial lamina
consists of subcutaneous fibres decussating posterior and anterior to the anus, but without bony attachments. (2) The sphincter ani superficialis constitutes the main portion of the muscle. It is attached posteriorly to the coccyx, and, anterior to the anus, it reaches the central point of the perineum. (3) The deep fibres of the muscle form, for the most part, a complete sphincter for the anal canal. They are continuous with the fibres of the levator ani: they encircle the anal canal, and blend anteriorly with the central point of the perineum and the transversus perinei superficialis muscle.
M. Corrugator Cutis Ani. The corrugator cutis ani consists of bundles of unstriped muscular fibres which radiate from the margin of the anal opening superficial to the external sphincter.