Crotch

Perineum (perineum) is a complex of soft tissues (skin, muscles, fascia) that close the exit from the cavity of the small pelvis.

The perineum occupies the area bounded from the front by the lower edge of the pubic symphysis, from behind - by the tip of the coccyx, and at the sides by the lower branches of pubic and sciatic bones and sciatic tubercles. If you take for the extreme crotch points of the cervical hillocks, in front - the lower point of the pubic symphysis, at the back - the tip of the coccyx, then the outline of the perineum can be compared with the rhombus.

The transverse line connecting the ischial hillocks divides this area into two parts, in the form of triangles. The anterior part was called the urogenital region (regio urogenitalis), and the lower one - the anal region (regio analis). Within the urogenital area is the urogenital diaphragm, and in the anal region - the diaphragm of the pelvis. Both diaphragms are adjacent to each other with their bases, and the apices are directed respectively to the pubic symphysis and coccyx.

In the narrow sense, the crotch is understood as the area located between the external genital organs in front and the rear passage from behind. This area corresponds to the tendon center of the perineum (centrum tendineum perinei). In women, this segment extends from the posterior margin of the genital cleft to the anterior margin of the anus, and in men from the posterior margin of the scrotum to the anterior margin of the anus. In the anteroposterior direction, a dark band passes through the perineal skin - the median seam of the perineum (raphe perineum), which in front of the men continues into the scrotum suture.

The genitourinary diaphragm (urogenital area) and the pelvic diaphragm (anal region) are muscular-fascial plates formed by two layers of muscles (superficial and deep) and fascia. In the anal region, the muscles of the pelvic diaphragm lie between its upper and lower fascia. Muscles of the genitourinary diaphragm are arranged in such a way that the deep layer is enclosed between the upper and lower fascia of the urogenital diaphragm. All this muscular-fascial plate from the side of the pelvic cavity is covered with the fascia of the pelvis, from the outside (from below) - the surface fascia.

The genitourinary diaphragm occupies the anterior part of the perineum and has the shape of a triangle, the vertex of which faces the pubic symphysis. The sides are bounded by the lower branches of the pubic and ischium bones, the base corresponds to the line connecting the ischial hillocks. Through the urogenital diaphragm in men passes the urethra, and in women - the urethra and the vagina.

Muscles of the genitourinary diaphragm are divided into superficial and deep. To the surface are 3 muscles: superficial transverse muscle of the perineum, ischial-cavernous and bulbous-spongy

The superficial perineal transverse muscle (m.transversus perinei superficialis) is paired, lying in the deep layer of subcutaneous fat. Begins on the lower branch of the ischium bone near the ischial hillock, goes transversely to meet the same muscle of the other side and ends in the tendon center of the perineum, formed by the thin flat tendons of these muscles. Some of the fibers of this muscle are weaved into the external sphincter of the anus and into the bulbous-spongy muscle of the opposite side. Surface transverse muscles participate in strengthening the tendon crotch center.

The sciatic-cavernous muscle (m.ischiocavernosus) is also paired, begins on the lower branch of the ischium. It is due to its medial side to the penis of the penis (in men) or the clitoris (in women). The muscle is attached to the cavernous body, part of this muscle with the tendon ending extends to the back of the penis, where it joins with the fibers of the same muscle of the opposite side. In women, this muscle is smaller than that of men. Sedal-cavernous muscles with a reduction contribute to erection of the penis or clitoris, squeezing the venous vessels.

The bulbous-spongy muscle (m.bulbospongiosus) in men originates from the seam and the lower surface of the bulb of the penis. The fibers go forward, laterally and upward, embrace the onion and spongy body of the penis to the right and left and attach to its belly coat and superficial fascia on the rear of the penis. With contraction, the muscle squeezes the bulb, the cavernous bodies and the dorsal vein of the penis, as well as the bulbourethral glands, participates in the erection, and also facilitates the ejection of sperm and urine from the urethra. In women, the bulbous-spongy muscle is paired, covering the vagina in the area of its opening (m.sphincter urethrovaginalis). The muscle begins on the tendon center of the perineum and the external sphincter of the anus, is attached to the dorsal surface of the clitoris, woven into its belly shell. On its way, the muscle is lower down to the glands of the vestibule. When contracting, the entrance to the vagina narrows, squeezes the large gland of the vestibule, the bulb of the vestibule and the veins emerging from it.

The deep muscles of the urogenital diaphragm include the transverse muscle of the perineum and the muscle - the sphincter of the urethra.

The deep perineal transverse muscle (m.transversus perinei profundus) is paired, looks like a thin plate, begins on the branches of the ischium and pubic bones. On the median line of the perineum, its flat tendon joins the tendon of the same muscle of the other side and participates in the formation of the tendon crotch center. Both muscles strengthen the urogenital diaphragm.

The muscle - the sphincter of the urethra (m.sphincter urethrae) begins partially on the lower branches of the pubic bones. The muscle bundles have a predominantly circular direction, embracing the membranous part of the urethra in men, and the urethra in women. In men, the bundles of fibers of this muscle are attached to the prostate gland, while in women they are woven into the vaginal wall. The muscle is an arbitrary compressor of the urethra. In women, the muscle also compresses the vagina.

Diaphragm of the pelvis

The diaphragm of the pelvis (diaphragma pelvis) occupies the posterior part of the perineum and has the appearance of a triangle, the vertex of which is directed towards the coccyx, and the corners are directed towards the ischium. Through the diaphragm of the pelvis both in men and in women passes the final department of the rectum.

The superficial layer of the muscles of the pelvic diaphragm is represented by an unpaired muscle - the external sphincter of the anus (m.sphincter ani externus). This muscle lies under the skin surrounding the end section of the rectum. It consists of several beams, the most superficial of which terminate in the subcutaneous tissue. The tufts beginning at the tip of the coccyx embrace the anus and terminate in the tendinous center of the perineum. The deepest bundles, surrounding the lower section of the rectum, adjoin the muscle that raises the anus. All bunches of the external sphincter of the anus at the contraction compress (close) the opening of the anus.

To the deep muscles of the pelvic diaphragm are two muscles that form the posterior part of the bottom of the cavity of the small pelvis. The muscle that lifts the anus (m.levator ani) is paired, has the shape of a thin triangular plate, forms a funnel with the same muscle on the other side, with the wide part facing upwards. The lower parts of both muscles, tapering, cover the rectum in the form of a loop. The muscle originates on the lateral wall of the small pelvis by several bundles. The front fascicles begin on the inner surface of the lower branch of the pubic bone, the lateral on the tendon arc of the muscle lifting the anus (arcus tendineum musculi levatoris ani). The tendon arch is an arcuate thickening of the pelvic fascia in the place where it forms the occlusal fascia. Bunches of right and left muscles that lift the anus are directed down and back, connect with each other, cover the rectum. Some of the fibers of these muscles are weaved into the prostate (in men), the vaginal wall (in women), and also into the wall of the bladder and rectum; the muscles themselves end at the tip of the coccyx in the form of an anal-coccygeal ligament (lig. Anococcygeum). When the muscle contracting the anus is contracted, the pelvic floor rises and rises, the lower (terminal) rectum section is pulled up and up, which is then squeezed. This muscle in women also compresses the entrance to the vagina and brings the back of the vagina closer to the front.

The coccygeal muscle (m.coccygeus) is paired, begins on the ischium awn and sacro-osteous ligament, is medial and posterior; is attached to the lateral margin of the coccyx and the tip of the sacrum. The bunches of this muscle are adhered from the medial side to the sacro-osteoid ligament, and are partly woven into it, strengthening the posterior part of the pelvic diaphragm.

The bottom of the pelvic cavity is closed by the diaphragm pelvis (diaphragma pelvis), which is supplemented in front of the urogenital diaphragm (diaphragma urogenitale).

The composition of the pelvic diaphragm includes both muscles that lift the anus (m. Levator ani), the coccygeal muscle and the external sphincter of the rectum (m. Sphincter ani externum).

The muscle lifting the anus, the paired, has a triangular shape and consists of pubic-coccygeal (M. Pubo-coccygeus), ilio-coccygeal and ischiococcygeal (m. Ileo-coccygeus). The entire muscular mass of the pelvic diaphragm is in the form of a bowl or dome that is turned downward, a concave surface facing upward, and a convex surface facing downward. In the middle of this dome there is a genital cavity through which the urethra, vagina and rectum come out.

The genitourinary diaphragm is triangular in shape. In its anterior part is the genitourinary sphincter (uro-genitale), in the posterior is the transverse deep perineum muscle (m. Transversus perinei profundus) associated with the surface layer muscles and left-handed.

The external layer of the pelvic floor muscles includes the external and internal sphincters of the anal opening (m. Sphincter ani externus, internus), the bulbous cavernous muscle (M. Bulbo-cavernosus), the transverse perinei superficialis (transversus perinei superficialis) and the sciatic-cavernous muscle (m. Ischiocavernosus). The outer layer of the muscles of the pelvic floor merges with its tendons into a strong fibrous formation - the tendon center of the perineum (centrum tendineum perinei).

The blood supply of the bottom of the pelvic cavity is carried out mainly by the branches of the internal sexual vessels (a. Pudenda interna). Blood supply to the perineum - external and internal sexual vessels (a. Pudenda externa et interna).

The innervation of the muscles of the pelvic floor occurs due to the branches of the sacral plexus (pli. Sacralis), the external genital nerve (pudendus), and the lumbar plexus (pl. Lumbalis).

Muscles of the bottom of the pelvic cavity are essential in maintaining intra-abdominal pressure, fixation of the abdominal cavity and pelvis.

[1], [2], [3], [4]

Vessels and nerves of the perineum

Blood supply to the perineum is carried out by the branches of the inner (deep) genital artery, which comes out of the pelvis cavity through a large sciatic hole, rounds the sciatic isthmus, and then through the small sciatic hole enters the sciatic-rectum fossa. Here the artery gives off several large branches: the lower rectal artery, the perineal artery and the dorsal artery of the penis or clitoris. Venous blood flows along the veins of the same name into the internal iliac vein. Lymphatic vessels flow into the superficial inguinal lymph nodes.

The innervation of the perineum is carried out along the branches of the genital nerve: along the nerve fibers of the lower rectal nerves, the perineal nerves, and the anal-coccygeal nerves-the branches of the coccygeal nerve.

Perineal development

In the embryo during development, the cavity of the cloaca is divided into the ventral section - the urogenital sinus and the dorsal part - the rectum due to the frontal urinary-uterine septum that grows into it. The urinary-intestinal septum expands in the caudal direction, reaches the cloacal plate, which is then divided into the anterior part - the urogenital plate and the posterior part - the anal plate. Each plate independently breaks through, resulting in holes in the anus and the urogenital opening. Around these holes from the ingrown into the thickness of the anal and urogenital plates of the mesoderm are formed muscle fibers. Initially, these fibers form sphincters, and then the muscle that lifts the anus (in the anal plate area), the perineum, and the other muscles that make up the genitourinary diaphragm.