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micturition, parturition, and laboured expiration. (2) They are also flexors of the vertebral column and pelvis-the muscles of both sides acting together; the vertebral column and pelvis are laterally flexed, when one set of muscles acts alone.
The posterior muscles of the abdominal wall and pelvis major include the psoas (major and minor) and iliacus, described already (p. 410), and the quadratus lumborum.
M. Quadratus Lumborum.-The quadratus lumborum lies in the posterior wall of the abdomen, lateral to the psoas, and extends between the iliac crest and the last rib. It arises from the posterior part of the iliac crest, from the iliolumbar ligament, and from the transverse processes of the lower lumbar vertebræ.
It is inserted, above, into the medial part of the inferior border of the last rib and the transverse processes of the lumbar vertebræ. Its lateral border is directed obliquely upwards and medially.
It is enclosed between the anterior and middle layers of the lumbo-dorsal aponeurosis (p. 437), between the psoas major muscle, in front, and the sacrospinalis behind.
Nerve-Supply. The quadratus lumborum is supplied directly by branches from the anterior rami of the first three or four lumbar nerves.
Actions. The muscle is a lateral flexor of the vertebral column, an extensor of the column and a muscle of inspiration.
FASCIÆ AND MUSCLES OF THE PERINEUM
FASCIÆ OF THE PERINEUM.
The superficial fascia of the perineum possesses certain special features. It is continuous with the superficial fascia of the abdominal wall, thigh, and buttock, and is prolonged on to the penis and scrotum. In the penis, it is devoid of fat and consists only of areolar tissue. In the scrotum, it is intermingled with involuntary muscular fibres, and constitutes the dartos muscle, which assists in suspending the testes and corrugating the skin of the scrotum. This fascia also forms the septum of the scrotum, which, extending upwards, incompletely separates the two testes and their coverings. In the female the superficial fascia, in which there is a considerable quantity of fat, takes a large share in the formation of the mons Veneris and labia majora pudendi.
The fascia over the posterior part of the perineum fills up the ischio-rectal fossæ, in the form of two pads of adipose tissue, on either side of the rectum and anal canal. Over the tuberosities of the ischium the fat is intermingled with bands of fibrous tissue closely adherent to the subjacent deep fascia.
The fascia in the anterior part of the perineum closely resembles the same fascia in the groin. It is divisible into a superficial fatty and a deeper membranous layer; the former continuous with the same layer in the thigh, and with the fat of the ischio-rectal fossa posteriorly. The deeper membranous layer is attached laterally to the pubic arch, posteriorly to the base of the fascia inferior of the urogenital diaphragm and in the median plane to the root of the penis (bulb and corpus cavernosum urethra) by a median raphe continuous, farther forwards, with the septum of the scrotum mentioned above. Anteriorly the fascia is continued over the spermatic funiculi to the anterior abdominal wall. The importance of this fascia lies in relation to the extravasation of urine from a rupture of the urethra in the perineum. By the fascial attachments the fluid is prevented from passing posteriorly into the ischio-rectal fossa, or laterally into the thigh. It is directed forwards into relation with the scrotum and penis, and along the spermatic funiculus to the anterior abdominal wall. The septum of the scrotum being incomplete, fluid extravasated on one side can pass across the median plane to the opposite half of the perineum and scrotum.
The deep fascia of the perineum exists only in the form of the delicate fascia of the muscles.
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.
Nerve-Supply. The external sphincter is supplied by the inferior hæmorrhoidal branch of the pudendal nerve (S. 3. 4.), by the perineal branch of the fourth sacral nerve, and by the deep perineal branch of the pudendal nerve (S. 3. 4.).
Actions. The muscle closes the anal aperture. It is a voluntary muscle.
M. Transversus Perinei Superficialis.-The transversus perinei superficialis is not always present. It consists of a more or less feeble bundle of fibres, which arises from the inferior ramus of the ischium and the fascia over it, and from the base of the fascia inferior of the urogenital diaphragm.
It passes obliquely over the base of the fascia inferior to be inserted into the central point of the perineum.
Nerve-Supply.-Deep perineal branch of pudendal nerve (S. 3. 4.).
Action. The two muscles acting together draw backwards and fix the central point of the perineum.
M. Bulbocavernosus.-The bulbocavernosus (O.T. ejaculator urinæ), in the male, surrounds the bulb, corpus cavernosum urethræ, and root of the penis. It is sometimes separ
ated into two partsposterior (compressor bulbi), and anterior (compressor radicis. penis). It arises from the central point of the perineum, and from a median raphe on the under surface of the bulb and corpus cavernosum urethræ.
The muscular fibres pass laterally and forwards and have a triple insertion: from behind forwards, (1) into the inferior surface of the fascia inferior of the urogenital diaphragm; (2) into the dorsal aspect of the corpus cavernosum urethræ; and (3), after encircling the corpora cavernosa penis, into the fascia covering the dorsum of the penis.
The ischiobulbosus, not always present, arises from the ischium, and passes obliquely medially and forwards over the bulbocavernosus, to be inserted into the raphe superficial to that muscle. It belongs to the same stratum as the transversus perinei superficialis and ischiocavernosus.
The compressor hemispheriorum bulbi is frequently absent. It consists of a thin cap-like layer of muscular fibres surrounding the extremity of the bulb under cover of the bulbocavernosus.
M. Bulbocavernosus.-The bulbocavernosus, in the female (O.T. sphincter vagina), is separated into lateral halves by the vaginal and urethral openings. It forms two thin lateral layers covering the bulb of the vestibule, and arises behind the vaginal orifice from the central point of the perineum.
Anteriorly it is inserted into the root of the clitoris, some of its fibres embracing the corpora cavernosa clitoridis so as to reach the dorsum of the clitoris.
Nerve-Supply.-Deep branch of the perineal nerve (pudendal, S. 3. 4.).
Actions. In the male.-The bulbocavernosus contracts the urethra in the emission of urine and semen, and is an accessory muscle in erection of the penis.
In the Female.-The muscle contracts the vaginal orifice, and compresses the bulb of the vestibule of the vagina.
M. Ischiocavernosus.-The ischiocavernosus (O.T. erector penis), in the male, covers the crus penis. It arises from the ischial tuberosity and the sacrotuberous ligament.
Passing forwards, it is inserted by a fascial attachment into the inferior surface of the crus penis, and into the lateral and dorsal aspects of the corpus cavernosum penis.
The ischiocavernosus (O.T. erector clitoridis), in the female, has a similar disposition, but is of much smaller size than in the male.
The pubocavernosus is an occasional slip arising from the pubic ramus, and inserted into the dorsum of the penis. It corresponds to the levator penis of lower animals.
Nerve-Supply. Deep branch of the perineal nerve (pudendal, S. 3. 4.).
FIG. 433.-THE FASCIE OF THE UROGENITAL DIAPHRAGM OF THE PERINEUM,
Diaphragma Urogenitale.-The sphincter urethræ membranacea and the transversus perinei profundus constitute the deeper muscular stratum of the perineum and form the urogenital diaphragm. They lie between two layers of fascia called the fascia inferior, and fascia superior of the urogenital diaphragm (O.T. superficial and deep layers of the triangular ligament).
M. Sphincter Urethra Membranacea.-The sphincter of the membranous urethra (O.T. compressor urethra) arises from the inferior part of the pubic ramus, and is directed medially, its fibres radiating so as to enclose the membranous urethra.
It is inserted into a median raphe, partly anterior to the urethra, but for the most part posterior to it. The fibres most intimately related to the urethra form a muscular sheath for the canal, and have no bony attachments.
M. Transversus Perinei Profundus.-The transversus perinei profundus consists of a bundle of fibres on each side which arises from the inferior ramus of the ischium just below the sphincter urethræ membranacea. It is inserted into a median raphe continuous with that of the sphincter urethræ membranacea. The muscle, in fact, constitutes a separate bundle below and behind the sphincter.
The ischiopubicus is a term applied to a feeble bundle of fibres which, when present, lies above and in front of the sphincter urethræ membranaceae. It arises from
the pubic ramus, and is inserted into a median raphe on the dorsum of the membranous urethra. This muscle is homologous with the compressor venæ dorsalis penis of lower animals.
The sphincter urethra 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 vagina), 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 FASCIA 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 peritoneum. 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.
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. 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 urethræ membranacea 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. It 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 transmission 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 it 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 urethræ membranacea and transversus perinei profundus is 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.