PelvisThe bony plevis is formed by four bones united at four joints.The bones are two hip bones in front and on the sides,and the sacrum and coccyx behind.The joints are the two sacroiliac joints,the ligaments between hip bone and spinal column,the pubic symphysis , the sacrococcgeal joint.

Sacroiliac jointIt is formed by the auricular surfaces of the sacrum and the ilium.The irregular articular surfaces of each bone contact closely with each other.The articular capsule is very tight and is strengthened by the anterior sacroiliac ligament,the posterior sacroiliac ligament and the interosseous sacroilac ligament.The movements of this joint are very limited because the joint is adapted to support the weight of the body.The joints are somewhat more movable during the pregnancy as the ligaments become more lax from hormonal action.

Ligaments between hip bones and spinal columnThe sacrotuerous ligament is situated at the lower and back part of the pelvis.It passes from the lateral margin of both the cacrum and coccyx to the medial margin of the ischial tuberosity.The sacrospinous ligament is a thin and triangular ligament,situated in front of the sacrotuberous ligament.It bridges between the lateral margin of both the sacrum and coccyx to the ischial spine.

These two ligaments convert the greater and lesser sciatic notches into the greater sciatic foramen and the lesser sciatic foramen.The foramina allow muscles,blood vessels and nerves to pass through between the pelvic cavity and the gluteal region.Sacrococcygeal joint (see the joints of vertebral column)

Pubic symphysisIt is a fibrocartilaginous joint formed by the interpubic disc between the two articular surfaces of the pubic bones.The disc may contain a small cavity and reinforced by some ligaments.The superior pubic ligament connects the two pubic bones together superiorly.

The arcuate pubic ligament connects the two pubic bones inferiorly,and forms the upper boundary of the pubic arch.No perceptible movements take place at the pubic symphysis.However,during the later stage of gestation and parturition,the interpubic disc tends to become more pliable and allows some separation of the pubic symphysis.

The pelvis is divided by the plane of the pelvic inlet or superior aperture of the pelvis into two parts:The upper part is known as the greater or false pelvis.the lower part is known as the lesser or true pelvis.The plane of the pelvic inlet passes from the sacral promontory to the upper margin of the pubic symphysis.The greater pelvis includes the two iliac fossae,and forms a part of the posterior abdominal wall.The lesser pelvis contains the pelvic viscera.

The lesser pelvis The lesser pelvis includes the plevic inlet,the plevic outlet,the plevic cavity,the plevic axes,the plevic walls and the pelvic diaphragm.The pelvic inlet is an oblique plane,making an angle of 50 to 60 degrees with the horizontal.It is bounded posteriorly by the sacral promontary,anteriorly by the upper margin of the pubic symphysis,and on each side by the linea terminalis.

The linea terminalis includes the anterior margin of the ala of the sacrum,the arcuate line,pecten pubis,and the pubic crest.The pelvic inlet is heart-shaped in the male,and is widest in its posterior part.In the female,it is oval,and is widest more anteriorly than in the male.Posterorly,the inlet is indented by the sacral promontory,more so in the male than in the female.

The pelvic outlet is bounded anteriorly by the arcuate pubic ligament;posteriorly by the coccyx;and on each side by the ischiopubic rami or side of the pubic arch,the ischial tuberosities and the sacrotuberous ligaments. The pubic arch is formed by the ischiopubic rami of the two sides and by the lower margin of the pubic symphysis which is rounded off by the arcuate pubic ligament. These arches meet below the pubic symphysis to form the subpubic angle.

The cavity between the pelvic inlet and the pelvic outlet is called plelvic cavity.The pelvic cavity is continuous above with the abdominal cavity at the plevic inlet,and is limited below by the plevic diaphragm.The cavity is curved in such a way that is is first directed downwards and backwards,and then downwards and forwards.It has unequal walls, measuring only about 5 cm anteriorly and 15 cm posteriorly.The cavity is more larger in female than in the male.

The axis of the pelvic inlet transverses its enter at right angles to its plane,directed down and backwards.When prolonged (projected) it passes through the umbilicus and midcoccyx.An axis is similarly established for the pelvic outlet:projected upwards it impinges on the sacral promontory.Axes can likewise be constructed for any plane,and one for the whole cavity is a concatenation of an infinite series of such line.

It follows the curvature of the cavity ,indicated by the profile of the sacrum and coccyx in lateral views.The form of this pelvic axis and the disparity in depth between the anterior and posterior contours of the cavity are prime factors in the mechanism of fetal transit in the pelvic canal.

Wall of the pelvisInternal iliac arteryThe internal iliac artery is a terminal branch of the common iliac artery.In the fetus,internal iliac artery is double the size of the external iliac artery because it transmits glood to the placenta through the umbilical artery, which is a branch of internal iliac artery..

After birth the proximal part of umbilical artery persists to form the proximal part of superior vesical artery,the rest of it degenerates into a fibrous cord,the medial umbilical ligament.The internal iliac artery begins in front the sacroiliac joint.It is divided into anterior and posterior divisions

Branches of anterior divisionIn the male,it gives off six branches:superior vesical artery;obturator artery,middle rectal artery,inferior vesical artery,inferior gluteal artery;and internal pudendal artery.In the female,it gives off seven branches.The inferior vesical artery is replaced by the vaginal artery.The uterine artery is the seventh branch

Superior vesical arteryThe proximal part of the superior vesical artery represents the persistent part of the umbilical artery.It supplies to the upper part of the urinary bladder.One of these branches gives off the artery to the ductus deferens.

Obturator arteryIt runs forward and downwards,and passes through the obturator foramen to leave the plevis and enters the thigh.It gives off branches to iliac fossa and the urinary bladder,and a pubic branch ,which anastomoses with the pubic branch of the inferior epigastric artery.Middle rectal arteryIt usually arises with the inferior vesical artery and supplies the rectum and the prostate and seminal vesicles.

Inferor vesical arteryIt usually arises with the middle rectal artery and supplies the trigone of the bladder,the prostate,the seminal vesicles,and the lower part of the ureter.Sometimes the artery to the ductus deferens arises from the inferior vesical artery.

Inferior gluteal arteryIt is the largest branch of the anterior division of internal iliac artery.It runs downwards and enters the gluteal region through the lower part of the greater sciatic foramen below the piriformis.It supplies chiefly the buttock and the back of the thigh.

Internal pudendal arteryIt is the smaller terminal branch of the anterior division of the internal iliac artery.It suppplies the perineum and external genitalia.It leaves the pelvis and passes through the greater sciatic foramen below the piriformis,thus entering the gluteal region.In the gluteal region,it passesthrough the lesser sciatic foramen and enters the pudendal canal.

In the pudendal canal,the artery gives off the inferior rectal artery,the perineal artery.The internal pudendal artery continues into the deep perineal space as the artery of the penis or of the clitoris.The artery of the penis or clitoris is divided into the deep and dorsal arteries of the penis or of clitoris.

Vaginal arteryIt corresponds to the inferior vesical artery of the male,and supplies the vagina,the bulb of the vestibule,the base of the urinary bladder,and the adjacent part of the rectum.Uterine artery (see Chapter)Branches of posterior divisionIt gives off:Iliolumbar artery;two lateral sacral arteries;and superior gluteal arteries.

Iliaolumbar arteryIt runs upwards in front of the sacroiliac joint and divides into the lumbar and iliac branches.The lumbar branch supplies the psoas,the quadratus lumborum and the erector spinae.Its spinal branch supplies the cauda equina.The iliac branch supplies the iliac fossa and iliacus.Lateral sacral arteriesThese are usually tow in number,upper and lower.They run downward and medially over the sacral nerves.Their branches enter the four anterior sacral foramina to supply the contents of the sacral canal and the muscles, skin on the back of the sacrum.

Superior gluteal arteryIt runs backwards and leaves the pelvis through the greater sciatic foramen above the piriformis.For further course see gluteal region.

Internal iliac veinIt ascends with the internal iliac artery,and joins the external iliac vein to form the common iliac vein at the pelvic brim.Its tributaries correspond with the branches of the artery.The tributaries are as follows.Superior gluteal vein is the largest tributary;inferior gluteal vein;internal pudendal vein;obturator vein and lateral sacral veins.

Veins arising from the plexuses of the plevic viscera:The rectal venous plexus is drained by the superior,middle and inferior rectal veins;the prostatic venous plexus is drained into the vesical and internal iliac veins;the vesical venous plexus is drained by the vesical veins;the uterine venous plexuses are drained by the uterine veins;and the vaginal venous plexuses are drained by the vaginal veins.

Nerves of the pelvis:1.Sacral plexusThe sacral plexus is formed by the lumbosacral trunk and the ventral rami of the first to third sacral nerves,and part of the fourth sacral nerve.The lumbosacral trunk is formed by the descending branch of the ventral ramus of nerve L4 and the whole of L5.The trunk descends over the ala of the sacrum and joins with nerve S1.

The main plexus lies in front of the piriformis.Before uniting to form the plexus,the ventral rami give off:Twigs to the piriformis;the levator ani,the coccygeus,the sphincter ani externus;and the plevic splanchnic nerves.The plexus tends to divide into ventral and dorsal divisions.Branches derived from both dorsal and ventral divisions are the sciatic nerve and posterior cutaneous nerve of thigh.

Branches from dorsal division are the superior gluteal nerve,the inferior gluteal nerve,nerve topiriformis and perforating cutaneous nerve.Branches from ventral division are muscular branches to the quadratus femoris,the obturator internus,the levator ani,the coccygeus,the sphincter ani externus. Pudendal nerve and pelvic splanchnic nerves.

Coccygeal plexusIt is formed by the ventral rami of spinal nerves S4 (descending branch),S5 and the coccygeal nerve.The three nerves join on the plevic surface of the coccygeus to form a small plexus known as the coccygeal plexus.It gives off the anococcygeal nerves,which supply the skin in the region of the coccyx.

Pelvic autonmic nervesPelvic sympathetic systemThe pelvic part of the sympathetic chain runs downwards and slightly medially over the body of sacrum,and then along the medial margins of the anterior sacral foramina.The two chains unite in front of the coccyx to form a small ganglion impar.The chain bears four sacral ganglia on each sede and thesingle ganglion impar in the central part

The branches of the chain are:Grey rami commicans to all sacral and coccygeal ventral rami;branches to the inferior hypogastric plexus from the upper ganglia;branches to the median sacral artery from lower ganglia;branches to the rectum from the lower ganglia;and branches to the glomus coccygeum.The inferior hypogastric plexus one on each side of the rectum and other pelvic viscera is formed by:the hypogastric nerve from the superior hypogastric plexus and the plevic splanchnic nerves.

Pelvic splanchnic nerves represent the sacral outflow of the parasympathetic nervous system.The nerves arise as fine filaments from the ventral rami of S2,S3 and S4.They join the inferior hypogastric plexus and are distributed to the plevic organs.Some parasympathetic fibres ascend with the hypogastric nerve to the superior hypogastric plexus and thence to the inferior mesenteric plexus which is distributed to the descending colon,the sigmoid colon and the rectum

Pelvic muscles and pelvic diaphragmThe pelvic muscles include two goups:The pirifomis and obturator internus,which are describbed with the muscles of the lower limbs;and the levator ani and coccygeus,which with the corresponding muscles of the opposite side,form the pelvic diaphragm.

The diaphragm separates the pelvis from the perineum. The levator ani and coccygeus may regarded as one morphological entity,divisible from before backwards into the pubococcygeus,the iliococcygeus and the ischiococcygeus or coccygeus.They have a continuous linear origin from the body of the pubis,the tendinous arch or the obturator fascia and the ischial spine.The muscle fibres slope downwards and backwards to the midline,making a gutter-shaped pelvic floor.

The levator aniThe levator ani is divisible into a pubococcygeus part and an iliococcygeus part.The levator ani is supplied by a branch from the fourth sacral nerve;and a branch either from the inferior rectal nerve,or from the pudendal nerve.Pubococcygeus part The anterior fibres of this part arise from the meidal part of the body of the pubis.In the male these these fibres surround the prostate called the levator prostatae.

In the female these fibres surround the vagina called sphincter vaginae. The middle fibres arise from the lateral part of the body of the pubis.They form the puborectalis. The posterior fibres of the pubococcygeus arise from anterior part of the tendinous arch.They get attached to anococcygeal ligament and tip of coccyx.

Ilococcygeus partThe fibres of this part arise from the posterior part of the tendinousarch and the ischial spine.They are inserted into the anococcygeal ligament and the side of coccyx.The coccygeusThis muscle is also called ischiococcygeus.It is triangular in shape.Its fibres arise from the ischial spine and the sacrospinous ligament.It is inserted into the side of the coccyx,and into the fifth sacral vertebra.The muscle is supplied by a branch derived from the fourth and fifth sacral nerves.

The pelvic diaphragmThe pelvic diaphragm is a sheet consisting of two muscles,the levator ani and coccygeus,two fasciae,the superior and inferior fasciae of plevic diaphragm.This diaphragm supports the pelvic organs,seals the inferior opening of the bony pelvis,and lifts superiorly to help release feces during defecation.The plevic diaphragm is pierced by the rectum,the urethra and the vagina.