The Striated Urogenital Sphincter Muscle in the Female THOMAS M

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THE ANATOMICAL RECORD 205223-232 (1983)

The Striated Urogenital Sphincter Muscle in the Female THOMAS M. OELRICH Department of Anatomy, University of Michigan, Ann Arbor, Michigan 48109

ABSTRACT Striated muscle associated with the female urethra and vagina constitute a continuous mass which appropriately may be called the urogenital sphincter. Though continuous, the muscle may be separated into two parts-one that surrounds the urethra, and the other surrounding the urethra and vagina. The individual muscle fibers are small and are embedded in connective tissue and infiltrated with smooth muscle which obscures the visibility of the muscle to gross dissection. Developmentally the muscle primordium is laid down around the urogenital sinus and urethra early, and foreshadows the anatomical arrangement that is maintained in the adult with little change. The urogenital sphincter muscle extends from the base of the bladder where it lies within the pelvic cavity and continues through the urogenital hiatus of the pelvic diaphragm to expand around the vagina in the perineum. Additional fibers attach to the ischiopubic rami and constitute a compressor of the urethra. As a result there is no superior fascia of the so-called “urogenital diaphragm” which closes off a deep perineal compartment or forms a floor of the urogenital hiatus.

Few anatomists and probably fewer students Henle (1873) unfortunately combined the have seen the urogenital sphincter muscle in muscles described by Luschka into a single unit, the female. Indeed the original literature and the M. transversus perinei profundus, and fur- early reference texts of gross anatomy provide thermore described the urogenital diaphragm descriptions that are incomplete, ambiguous, as consisting of two aponeuroses with the M. and controversial. Only two muscles, M. transversus perinei profundus between these sphincter urethrae, and M. transversus perinei layers. He accurately indicated that the dia- profundus, are listed in the most recent Nom- phragm contained quantities of smooth muscle ina Anatomica (Fourth edition). in which the striated muscle fibers were rec- Early anatomists recognized muscle fibers ognizable only singly and sometimes not at all. surrounding the urethra. Wilson (1809) de- He did not recognize the urethral sphincter scribed the male urethral sphincter and indi- muscle, but he stated that the muscle of the cated that he had seen a similar muscle in the urogenital diaphragm could not be a urethral female surrounding the urethra and attaching sphincter. Henle’s description has been the to the pubis in front and the perineal body source of much subsequent confusion, not only behind. Guthrie (1849,in describing the male for giving the term M. transversus perinei pro- urethral sphincter as lying between two layers fundus to all of the muscle of the region but of deep perineal fascia, indicated that the same by describing the so-called “urogenital dia- muscle could be seen in the female, but with phragm,” which no subsequent researchers have lateral attachments. confirmed yet which all subsequent textbook Luschka (1864)described an M. constrictor writers have reiterated with unerring accu- cunni profundus as a type of vaginal sphincter racy. lying deep to the vestibular bulb and extending Leeshaft (1884) described the urogenital forward to the sides and ventral to the urethra. muscle including a M. constrictor urethrae, According to his description this muscle con- which surrounded the urethra and extended tinued along the urethra to the base of the from the base of the bladder to the perineal bladder. The fibers did not surround the ur- membrane, and a M. constrictor vestibulae s. ethra, but only attached to the anterior wall sphincter vaginae (M.constrictor cunniprofun- of the vagina. Luschka also described a M. dus of Luschka), but indicated that it did not transversus perinei profundus, which extended from the ischium to the perineal body behind the greater vestibular gland. Wived January 21,1982; accepted October 11,1982.

0003-276W83/2052-0223$03.00 0 1983 ALAN R. LISS, INC. 224 T.M. OELRICH pass behind the vagina. While understanding bladder. He described the sphincter as con- the continuity of the two previous muscles he sisting of completely circular fibers in his young defined a M. transversus urethrae and a M. specimens. He perceived that the more distal transversus vaginae extending from the lateral fibers of the sphincter of the urethra inserted wall of the urethra and the anterior wall of the into the vaginal wall. vagina to the descending process of the pubis. Hutch and Rambo (1967) identified the ure- He also included a separate M. transversusper- thral sphincter extending to the bladder neck inei profundus extending from the ischial tub- and surrounding the middle third of the ur- erosity to the perineal body behind the vagina. ethra, though they conventionally utilized the Leeshaft recognized that the fascia of the pel- “urogenital diaphragm” as its location. vis did not separate the pelvis from what was With few exceptions, modern textbooks of called the urogenital diaphragm by Henle, but anatomy and reference texts give sketchy and that the fascias formed a urethrovaginal cap- essentially incorrect descriptions of the female sule continuous with the pelvic cavity above urogenital musculature. Those authors who do and closed off below by a perineal membrane. refer to the literature seem to make an arbi- Holl (1897) reiterated the descriptions of trary selection of their reference descriptions. previous workers and included the M. trans- Thus, though some aspects of the musculature versus perinei profundus and the M. sphincter have been accurately described, confusion per- urethrae s. urethrovaginalis as parts of the uro- sists in anatomical accounts of this region. As genital diaphragm of Henle. Holl considered a result, no complete and accurate illustrations the M. transversus urethrae of Leeshaft to be are available. Without a doubt this confusion part of the sphincter urethrae muscle, and the is due in part to the difficulty in dissecting the M. transversus vaginae of Leeshaft as part of region since the muscle is embedded in dense the M. transversus perinei profundus. investments of connective tissue; the muscle Kalischer (1900), in the most complete and fibers are smaller than striated fibers through- accurate description, reviewed the findings of out the rest of the body, and there are large all previous researchers and added his own ob- quantities of smooth muscle associated with servations concluding that the muscle con- the striated fibers. Hayek (1960) compared the sisted of a M. sphincter urogenitalis with two size of the individual striated fiber of the ure- parts-a pars urethrovaginalis and a pars ur- thral sphincter muscle with other striated ethralis. The pars urethrovaginulis enclosed the muscles of the human and found them to be urethra and vagina, and the pars urethralis 30%smaller. Oelrich (1980) described the size encircled the middle third of the urethra, Kal- of the muscle fiber and connective tissue in- ischer recognized a series of transverse fibers vestment of the muscle fiber in the male, and called the M. urethrotransversales “if they are Gosling (1979) defined these muscle fibers as at all present,” which he indicated to be very exclusively “slow-twitch in distinction to other weakly developed, but he observed that they mixed (slow- and fast-twitch) striated fibers were like the M. transversus urethrae and the found throughout the body. M. transversus vaginae of Leeshaft, not the M. It is the purpose of this paper to describe the transversus perinei profundus of Henley and striated urogenital sphincter musculature in Holl. Kalischer recognized that the true M. the female, to adjudicate the various descrip- sphincter urethrae lies within the urogenital tions extant, and to relate these muscle masses hiatus of the pelvic diaphragm and extends to to the various fascial planes and compartments the bladder. of the pelvis and perineum. Recent workers have limited their observations to the urethra and its striated sphincter. MATERIALS AND METHODS Ricci et al. (1950) reiterated that there was a Gross dissections were attempted under low striated sphincter surrounding the middle third magnification, but these efforts were initially of the urethra while indicating that they found found to be useless since dense connective tis- no fascial sheets “(superior diaphragmatis uro- sue and associated smooth muscle obscured the genitalis inferior and superior) and no com- striated muscle fibers. Subsequently the ur- partment (superficial and deep perineal) pierced ethra, vagina, rectum, and perineum were re- by the urethra.” moved en bloc, sectioned serially, and stained Gil Vernet (1953) described and illustrated with trichrome stains. Sections were made in the urethral sphincter muscle in the middle transverse, sagittal, and frontal planes. Each third of the urethra and commented upon the half of an individual specimen was sectioned more proximal fibers that reach the base of the in a different plane. The pelves from 14 fetuses, FEMALE UROGENITAL SPHINCTER MUCSLE 225 ranging from 66 mm CR to term were serially border of the sphincter can be established. Fi- sectioned and examined in conjunction with 29 bers of the primordial sphincter, behind the series of fetuses from the University of Mich- tuberculum sinuale, do not intermingle with igan embryology collection. Fourteen pelves the external anal sphincter but lie at a higher from term to 37 years were serially sectioned level. and examined. After the anatomy was con- In a slightly older fetus, 163 mm CR, (Fig. firmed by sectioned material the region was 7), sphincter fibers can be identified on the mid- dissected under low magnification. These ad- line between the primordial urethra and the ditional 29 gross dissections from term to 30 primordial vagina, thus establishing the com- years proved to be productive and adequately plete primordial urethral sphincter muscle. confirmed spatial and fascia1 relationships. In the 240-mm CR fetus the mesenchyme has completely differentiated so that striated OBSERVATIONS fibers are evident. Simply described, the pri- Early Development mordial urogenital sphincter in the female The disposition of the urogenital sphincters consists of two distinct elements: 1)a sphincter can be understood best by examining the de- of the urethra, and 2) a sphincter of the uro- veloping fetus, which shows the arrangement genital sinus. The elements are continuous and of mesodermal condensations ultimately dif- extend from the base of the bladder to the per- ferentiating to striated muscle. In a 60-mm CR ineal membrane lying within the pelvic cavity, fetus (Fig. l), just below the vesical neck, the in the urogenital hiatus, and in the perineum. mesenchyme thickens anterior to the vesi- Though modifications of this arrangement oc- courethral canal. Dorsal to this canal are the cur throughout subsequent growth, the basic fused paramesonephric ducts which join the pattern does not change. This distinguishes the urogenital sinus at the level of the tuberculum development of the male from the female, as sinuale (Fig. 2) (Mullerian tubercle) and thus in the male the development of the prostate separate off the primitive urethra above, from shapes and displaces the urethral sphincter the urogenital sinus below. The thickened (Oelrich, 1980). mesenchyme lies ventral and lateral to this Growth to term shows only a single modifi- junction (Fig. 2). Caudally the thickened mes- cation in which the lower border of the uro- enchyme completely surrounds the urogenital genital sphincter extends laterally to the is- sinus (Fig. 3). The proximal fibers will become chiopubic ramus below the pelvic diaphragm. a urethral sphincter and the distal fibers a ur- This is not readily definable early because of ethrovaginal sphincter. the disproportionately large size of the devel- In an Ill-mm CR fetus (Fig. 4) sectioned in oping vagina which fills the space between the a frontal plane, the thickening mesenchyme ischiopubic rami. extends from the base of the bladder to the In the first two decades gross dissection of vestibular bulb demonstrating the continuity the sphincter mechanism is relatively produc- of the two parts. With the location of the pelvic tive with low magnification. However, the sub- diaphragm (Fig. 4), it is evident that the uro- sequent increases in the density of connective genital sphincter primordium lies in the pelvic tissue and smooth muscle obstruct the visibil- cavity, in the urogenital hiatus (between the ity of the striated muscle so that dissection halves of the pelvic diaphragm) and in the per- becomes more difficult later. ineum. Adult In a 140-mm CR fetus (Fig. 5) on a sagittal plane just lateral to the urethral wall, the en- Complete development of the urogenital tire urogenital sphincter primordium can be sphincters changes the proportional distribu- seen extending from the base of the bladder to tion of the muscle seen in earlier decades. Kal- the vestibular bulb. Fibers can be identified ischer (1900) emphasized the continuity of the between the primitive urethra and the para- muscle masses by naming them the M. sphinc- mesonephric duct and farther caudally fibers ter urogenitalis with a pars urethralis and a surrounding the beginning of the urogenital pars urethrouaginalis. The use of such termi- sinus. Immediately caudal to the primordial nology seems logical and will be maintained sphinder are the vestibular bulb and the greater here. In the adult these two parts lie in dis- vestibular gland, which maintains these po- tinctly different anatomical areas though they sitions in the adult. In the same series on the are continuous with one another. The pars ur- midsagittal plane (Fig. 6), the relations be- ethralis lies within the pelvic cavity; the pars tween the tuberculum sinuale and the lower urethrovaginalis lies in the perineum. The per- 226 T.M. OELRICH tral side and thins as it Dasses to the dorsal Abbreviations side of the urethra (Fig. fl).There appears to be a dorsal septum or a raphe into which the AL Arcuate pubic ligament fibers attach (Fig. 11).The size of this septum AS External anal sphincter B Bladder and the degree to which some striated fibers BS Bulbospongiosus muscle cross the midline vary with the individual. The ccc Corpus cavernosum clitoris presence of a fibrous septum or raphe would cu Compressor urethrae muscle change the manner in which the sphincter fi- IC Ischiwavernosus muscle IP Ischiopubic ramus bers constrict the urethra, although the major IR Ischial ramus content of this apparent septum is the circular MD Fused paramesonephric ducts layer of the smooth muscle of the urethra. The 01 Obturator internus muscle PD Pelvic diaphragm orientation of the urethral sphincter fibers is PF Pelvic fascia predominantly circular (Figs. 11,13,17),though PM Perineal membrane groups of fibers run obliquely within the PS Pubic symphysis sphincter. In the proximal part some fibers ex- R Rectum SM Smooth muscle of urethrovaginal compartment tend vertically into the bladder muscle. A few su Urogenital sinus peripheral fibers, instead of encircling the ur- TS Tuberculum sinuale (Miillerian tubercle) ethra, attach to the vaginal wall or into ad- Tv Transverse vaginal muscle jacent connective tissue (the endopelvic fascia). U Urethra UGS Urogenital sphincter primordium There is an infiltration of smooth muscle us Urethral sphincter throughout the length of the sphincter. The WS Urethrovaginal sphincter striated fibers appear to lie in the plane of the V Vagina circular smooth muscle of the urethra. Smooth VB Vestibular bulb VG Greater vestibular gland muscle bundles from the bladder overlie the w Veaicourethral canal proximal end of the urethral sphincter (Fig. vw Vaginal wall 13). The location of the urethral sphincter cor- responds precisely with the area of highest ure- ineal part (Fig. 15) parallels the ischiopubic rami and is therefore at an angle of approximately 130" with the urethral part (Fig. 17). It should be remembered that the urethra itself is not a straight tube but is concave ventrally. Fig. 1. Cross section of a female urethra in a 60-mm CR The continuity between the two parts lies in fetus just caudal to the bladder. x 17. the urogenital hiatus of the pelvic diaphragm just dorsal to the pubic symphysis. Fig. 2. Cross section of a female urethra in a 60-nunCR fetus at the level of the tuberculum sinuale. x 17.

M. Sphincter Urogenitalis (Pars Urethrae) Fig. 3. Cross section of a female urethra in a 60-mm CR fetus through the urogenital sinue. Note the position of the M. sphincter urethrae PNA. The M. sphincter pelvicdiaphragm. x 17. urethrae surrounds the urethra in the middle third of its length for approximately 1.5 cm Fig. 4. Coronal section of a Ill-mm CR female fetus (Figs. 13, 16, 17). It begins at the base of the through the bladder, urethra, and urogenital sinus. x 10. bladder, and caudally is continuous with the perineal component of the urogenital sphinc- Fig. 5. Saggital section of a 140-mm CR female fetus ter, M. compressor urethrae. As previously ex- demonstrating the extent of the developing urogenital pressed in the developmental considerations, sphincter primordium. x 9. the undifferentiated mesenchyme completely Fig. 6. Median section of a 140-mm CR fetus. Note por- surrounds the urethra; however, in the com- tion of urogenital sphincter primordium between tubercu- pletely developed sphincter, the striated fibers lum sinuale and rectal wall. x 9. vary in their density and degree of encircle- ment of the urethra. In the child striated fibers Fig. 7. Median section of a 163-mm CR female fetus. completely surround the urethra (Fig. 8). In Note urethral sphincter primordium between urethra and the adult, the sphincter is thickest on its ven- primordial vagina. x 9. FEMALE UROGENITAL SPHINCTER MUCSLE 227 228 T.M. OELRICH FEMALE UROGENITAL SPHINCTER MUCSLE 229 thral closure pressure as measured by Tanagho with the corresponding fibers of the opposite and Smith (1968). side of the body, forming a broad arcing muscle (Figs. 10,15). As the band reaches the urethra M. Sphincter Urogenitalis (Pars it rotates, so that its dorsal edge becomes in- Urethrovaginalis) ferior (Fig. 15) (located at the plane of the ar- M. compressor urethrae, nom. nou. (M.trans- cuate pubic ligament) and its ventral edge be- versus urethrae). Distal to and directly contin- comes superior. The superior edge lies within uous with the lower border of the urethral the urogenital hiatus of the pelvic diaphragm sphincter (Figs. 9, 10, 12-17) is a bundle of and is continuous with the lower fibers of the fibers which had been identified previously, but ventral part of the urethral sphincter (Figs. 13, was described in a variety of different ways. 14,16,17)where it lies behind and deep to the The muscle begins as a small tendon approx- pubic symphysis. Although most of the muscle imately 2 mm in diameter attaching to the passes ventral to the urethra (Figs. 12,13) some ischiopubic ramus laterally at a point near the few deep fibers attach to the lateral wall of the anterior border of the ischial tuberosity or on urethra. Leeshaft (1884) named these latter a plane at the posterior border of the vagina fibers the M. transversus urethrae, though he (Figs. 16, 17). The muscle extends forward to- was apparently not aware of the large mass of ward the anterior surface of the urethra, thick- muscle passing ventral to the urethra. The M. ens to a band of approximately 6 mm wide compressor urethrae is continuous with the M. (Figs. 9, 12, 13), and then becomes continuous sphincter urethrouaginalis along the inferior border of the M. compressor (Figs. 16, 17). Functionally, the M. compressor urethrae can compress the urethra from its ventral position. Because it approaches the urethra parallel to Fig. 8. Cross section of the left half of a female pelvis 1 the ischiopubic rami (at an angle of 130" to the year old, through the urethral sphincter muscle just caudal urethra), it additionally can have the effect of to the bladder. Note position of the pelvic diaphragm. x 2. pulling the urethral meatus caudally and inferiorly (Figs. 15,16). In combination with the Fig. 9. Cross section of the left half of a female pelvis 1 action of the pelvic diaphragm (elevating the year old demonstrating the upper border of the compressor bladder), it assists in elongation of the urethra. urethrae muscle anterior to the urethra. x 2. Lapidea (1958) emphasized the importance of urethral elongation as a means of providing Fig. 10. Cross section of the left half of a female pelvis 1 year old demonstrating the lateral extent of the compres- continence. sor urethrae muscle. Note absence of fibers between the Variations of this pattern do exist. Some fi- urethra and vagina; also note the proximity of the corpus bers may appear to attach to the transverse cavernosum clitoris to the anterior border of the compressor ligament of the perineum, thus giving rise to urethrae muscle. x 2. an older term, M. ischiopubicus. Occasionally the M. compressor urethrae may join the ur- Fig. 11. Cross section of an adult urethra and vagina demonstrating the urethral sphincter muscle at the level of ethrovaginal sphincter near the anterior bor- the urogenital hiatus of the pelvic diaphragm. Note appar- der of the vagina rather than ventral to the ent septum in the posterior portion of the sphincter. Age 33 urethra. Its size may be reciprocal with that years; x 1.8. of the M. sphincter urethrouaginalis.

Fig. 12. Cross section of an adult urethra and vagina demonstrating the upper edge of the compressor urethrae muscle. Compare with Figures 9 and 10. Age 29 years; x M. Sphincter Urethrovaginalis (M. Sphincter 1.8. Vaginae BNA, M. Sphincter Vestibuli,M. Con- strictor Cunni Profundus). The M. sphincter Fig. 13. Sagittal section of an adult female urethra and urethrouaginalis (Figs. 15-17) is a thin, flat vagina. The section is slightly off of the midline so that the muscle approximately 5 mm broad which blends entire urethral sphincter muscle can be visualized. Note the continuity between the urethral sphincter muscle and the ventrally with the M. compressor urethrae. From compressor urethrae muscle. Age 29 years; X 1.8. the ventral side of the urethra its fibers extend dorsally along the lateral wall of the urethra Fig. 14. Coronal section of a female pelvis demonstrating and vagina immediately deep to the cephalic continuity of the urethral sphincter muscle and the com- edge of the vestibular bulb. It is separated from pressor urethrae. Note absence of any fascia which may the vestibular bulb by a barely perceptible, thin separate the pelvic structures from the perineal structures (the so-called superior fascia of the urogenital diaphragm). layer of the perineal membrane. None of its Age 16 years; x 2.6. fibers pass between the urethra and vagina, 230 T.M. OELRICH

Fig. 15. Perineal view of the urogenital sphincter mu- Fig. 17. Oblique view of complete urogenital sphincter culature with the penned membrane removed. Age 27 years; muscles, bladder, and vagina. Arrow indicates continuity of x 0.6. the vaginal wall beneath the muscle. Age 27 years; x 0.6.

Fig. 16. View of complete urogenital sphincter musculature, bladder, and vagina with the pubic symphysis removed and the ischial rami spread. Arrow indicates continuity of the vaginal wall beneath the muscle. Age 27 years; x 0.6. FEMALE UROGENITAL SPHINCTER MUCSLE 231 nor do any of its fibers pass in front of or ventral of arteries, veins, and nerves passing through to the vagina. Fibers continue dorsally to pass it. behind the vagina and interdigitate with the corresponding muscle of the opposite side. In Urethrovaginal Compartment. The urogeni- the first two decades the muscle is distinct and tal sphincter muscle lies above or cephalic to proportionately small. With the increased den- the perineal membrane (Fig. 14) which sepa- sity of the connective tissue of the perineal rates these muscles from the ischiocavernosis body, it becomes difficult to identify fibers be- and the bulbospongiosus muscles and the as- hind the vagina. sociated cavernous bodies. While surrounding The term M. sphincter vaginae is historically the urethra and vagina the muscle is enclosed appropriate; however, the muscle does not ex- within a compartment formed by the perineal clusively surround the vagina, and is morpho- membrane inferiorly and a superior fascia, logically and functionally a urethrovaginal continuous through the urogenital hiatus of sphincter. In fact, the two muscles M. com- the pelvic diaphragm with the fascias of the pressor urethrae and M. sphincter urethrova- pelvis. This is not the so-called “urogenital dia- ginalis share the mass of muscle lying ventral phragm” described by Henle, which he indi- to the urethra but caudal to the M. sphincter cated closed off the urogenital hiatus, but a urethrae (Figs. 12,13,16,17).The two muscles urethrovaginal capsule (compartment) contin- may be reciprocal in size. The continuity of this uous with the pelvic cavity as described by muscle with the M. compressor urethrae would Leeshaft. imply that they complement one another in The urogenital hiatus in the female is much compression, retraction, and elongation of the reduced in comparison to the male since fibers urethra. of the pubococcygeus muscle of the pelvic diaphragm insert into the lateral wall of the va- M. Transversus Vaginae. In additional layer gina. The hiatus is therefore anterior to the of striated muscle (M. transversus Vaginae of vagina, and transmits only the urethra and its Leeshaft, 1884)parallels the M.compressor ur- muscle (Fig. 14). ethrae and radiates from it to attach to the The combined superior fascia of the pelvic anterior portion of the lateral wall of the va- diaphragm (transversalis)and the attached en- gina, attaching just above the urethrovaginal dopelvic fascia pass around the border of the sphincter (Figs. 15-17). The M. compressor ur- urogenital hiatus (Fig. 14). Continuing through ethrae and M. transversus vaginae form a con- the hiatus, this layer passes dorsally to join tinuous muscle, but, because of the different the posterior border of the perineal membrane course, thickness, and attachments, it seems and form an “apparent” diaphragm. Laterally appropriate to maintain individual names for this fascia joins the obturator fascia (or fascia the various parts. Though its size and extent lunata) extending to the ischiopubic ramus. do vary, these fibers form a very thin, fan-shaped Anteriorly the thickened endopelvic fascia of muscle that seldom attaches to the posterior the bladder and urethra passes through the half of the vagina. urogenital hiatus joining the anterior edge of The M. transversus perineus profundus was the perineal membrane as the transverse lig- originally described by Luschka (1864) as ex- ament of the perineum. These fascias collec- tending from the ischial tuberosity to the per- tively form a compartment which may appear ineal body. Subsequently, because others may as a diaphragm in the perineum while supe- not have been able to find the muscle (Henley, riorly it is open and directly continuous with 1873; Holl, 1897), it became synonymous with the pelvic cavity (Fig. 14). If one considers the the M. transversus vaginae and ultimately with specializations of the endopelvic fascia, the me- the M. transversus urethrae. Kalischer could dial and lateral pubovesical ligaments, one not identify the muscle, and neither can this might say that the compartment is limited su- author. It is entirely possible that misidenti- periorly by these. fications have occurred because of the variable This compartment, in addition to the uro- extent of the perineal membrane. In many genital sphincter muscle, contains an exten- specimens this membrane appears to extend to sive mass of smooth muscle. It is difficult to the midpoint of the rectum. In this manner separate the smooth muscle from the layers of fibers of the M. transversus perineus superfi- fascia exiting from the pelvis. The smooth mus- ciulis may easily be contained within this fas- cle extends throughout the perineal region from cia. The posterior border of the perineal mem- the ischiopubic rami to the lateral wall of the brane can usually be identified by the presence urethra and vagina lying between the perineal 232 T.M. OELRICH membrane and the superior fascia of the ur- ACKNOWLEDGMENTS ethrovaginal compartment (Figs. 15-17). The I wish to express appreciation for the art definitive character of the posterior border of work provided by William Brudon. the perineal membrane is due in part to the This work was supported in part by a grant presence of this smooth muscle mass. In the from the United States Public Health Ser- first decade and a half there is only slight evi- vice-NIH 5R01 GM 09773-02. dence of smooth muscle. The quantity seems to increase with age, and the striated compo- LITERATURE! CITED nent becomes less and less evident. The fact Gil Vernet, S. (1953) Patologfa Urogenital. Tom0 11, Vol. I. that the striated muscle is not well fasciculated Biologia y Patologla de la Prostata. Edit. Paz Montalvo, and is covered with a relatively thick muscular Madrid. Goaling, J. (1979) The structure of the bladder and urethra fascia makes the separation ofthe smooth mus- in relation to function. Urol. Clin. North Am., 6:3138. cle from the striated muscle most difficult. Guthrie, B.J. (1845) On the Anatomy and Diseases of the As mentioned previously, variations do oc- Urinary and Sexual Organs. Lea and Blanchad, Phila- cur with the characteristics and proportional delphia. Hayek, H. (1960) Das Faserkaliber in den Mm. transversus relations of the striated muscles in the first perinei und Sphincter urethrae. Zeitseh. Anat. Entwick- decades. Increase in the presence of smooth lungsgeschichte., 121:455-458. muscle and the development of the perineal Henle, J. (1873) Handbuch der Systematischen Anatomie body also obstruct structural interpretations. des Menschen. Bd. II., Druck und Verlag von Friedrich Vieweg und Sohn, Braunschweig. Within the multipara, as might be expected, Holl, M. (1897) Die Muskeln und Faseien des Beckenaus- the perineal component of the urogenital ganges. In Handbuch der Anatomie des Menschen. Bar- sphincter muscles is extremely difficult to deleben., Gustav Fischer, Jena. identify. Hutch, J.A., and O.N.Rambo (1967) A new theory of the anatomy of the internal urinary sphincter and the phys- SUMMARY iology of micturation. J. Urol., 97:696-704. Kaliaeher, 0. (1900) Die Urogenitalmuskdatur dea Dammes. The striated urogenital sphincter muscle of Verlag von S. Karger, Berlin. the female consists of 1) a sphincter surround- Lapides, J. (1958) Structure and function of the internal vesical sphincter. J. Urol., 80:341-353. ing the middle third of the urethra, 2) a ur- Leeshaft, P. (1884) Uber die Muskeln und Fascien der Da- ethrovaginal sphincter surrounding the ur- mmgegend beim Weibe. Gegenbaurs Morphologisches ethra and vaginal vestibule collectively, and Jahrbuch, 9:475-532. 3) a compressor of the urethra arcing across Luschka, H. (1864) Die Anatomie des Menschlichen Beck- ens. Laupp and Siebeck, Tubingen. the ventral side of the urethra. Other variable Oelrich, T.M. (1980) The urethral sphincter muscle in the striated fibers may occur. These designated male. Am. J. Anat., 158:229-264. muscles are in continuity with one another Ricci, J.V., J.R. Lisa, and C.H. Thom (1950) The female ventral to the urethra, and are located within urethra. Am. J. Surg., 79:499-505. Tanagho, E., and D. Smith (1968) Mechanism of urinary the pelvic cavity, in the urogenital hiatus of continence. 1. Embryologic, anatomic and pathologic con- the pelvic diaphragm, and in the perineum. siderations. J. Urol., 100:640-646. Smooth muscle fibers may interlace the striated Wilson, J. (1809) A description of two muscles surrounding fibers to a variable degree. The perineal com- the membranous part of the urethra. Med. Chirurg. Soc. ponents of the urogenital sphincter are con- Lond. 1:175-180. tained in a urethrovaginal compartment that is continuous with the pelvic cavity.