Advertisements help pay for this website. Thank you for
and lymphatics of the abdomen and pelvis | Main
Anatomy Index | Urogenital
diaphragm and ischiorectal fossa
Last updated 30 March 2006
- The pelvis is the inferior part of the trunk and the pelvic cavity
is the basin-shaped inferior part of the abdominopelvic cavity, which is located inferior to the plane
of the pelvic brim.
- The pelvic cavity is bounded inferiorly by the pelvic diaphragm.
- This forms the pelvic floor and separates the pelvis from
The Bony Pelvis
- This is the skeleton of the pelvis.
- It surrounds the pelvic cavity and forms the pelvic girdle
for the attachment of the lower limbs.
- It is formed anteriorly and laterally
by the two hip bones and posteriorly by the sacrum and coccyx.
- Anteriorly, the two pubic bones meet at the pubic symphysis.
- The skeleton of the pelvis was covered in Medicine 1 (ANAT1006).
The Pelvic Brim
- The pelvic cavity is located inferior to the plane of
the pelvic brim.
- This is an oblique plane that forms an angle of about 55 degrees to the horizontal.
- It coincides with a line joining the sacral promontory
to the superior border of the pubic
- This line also gives the anteroposterior (AP) diameter
of the superior pelvic aperture of pelvic inlet.
- The pelvic brim is formed from the following structures:
- Superior margin of the pubic symphysis;
- The pubic crest;
- The pecten pubis (pectineal line of the pubis);
- The arcuate line of the ilium;
- The anterior border of the ala of the sacrum;
- And the promontory of the sacrum.
- The pelvis is divided into a pelvis major (false pelvis),
which is part of the abdominal cavity, and a pelvis minor (true or "obstetric" pelvis), which
contains the pelvic cavity.
The Pelvis Major
- The pelvis major is bounded anteriorly by the abdominal
wall, laterally by the iliac fossae, and posteriorly
by L5 and S1 vertebrae.
The Pelvis Minor
- It is limited inferiorly by the inferior pelvic
aperture (pelvic outlet).
- This is closed by the pelvic diaphragm that is composed
mainly of the levator ani muscles.
- Its inferior boundary corresponds roughly to a line joining the
tip of the coccyx to the inferior border of
the pubic symphysis.
- The cavity of the pelvis minor is the pelvic cavity and
it contains pelvic viscera (e.g., the urinary bladder).
- It is tilted anteroinferiorly when it is in the
The Walls of the Pelvis Minor
- The posterior wall, which is notably longer than its
anterior wall, is formed by the concave pelvic surface of
the sacrum and coccyx.
- The anterior wall is formed by the pubic symphysis, the body of
the pubis, and the pubic rami.
- The lateral walls are formed by the pelvic
aspects of the ilium and ischium.
The Superior Pelvic
Aperture (Pelvic Inlet)
- The pelvic inlet is variable in contour. Sexual, racial
and nutritional differences influence its shape.
- It is heart-shaped in males and some females.
- In most females, this opening is larger than in the
male and is rounded or oval
- The periphery of the pelvic inlet, formed by the pelvic brim,
is indicated by the linea terminalis (iliopectineal
- This terminal line is an oblique ridge on the internal surface of the ilium, which is continued on the pubis.
- It forms the inferior boundary of the iliac fossae and separates the true and false pelves.
The Inferior Pelvic
Aperture (Pelvic Outlet)
- The pelvic outlet is bounded:
- Posteriorly by the sacrum and coccyx;
- Anteriorly by the pubic symphysis;
- And laterally by the ischial tuberosities.
- It is because of this that it does not have a smooth contour.
- The plane of this aperture makes an angle of 10-15 degrees
with the horizontal when the pelvis is in the anatomical position.
- The greater and lesser sciatic
notches between the sacrum, coccyx and the ischial tuberosities are divided
into the respective foramina by the sacrotuberous and sacrospinous
- These ligaments give the pelvic outlet a diamond-shape.
- The subpubic angle is narrow
in males and wide in females.
Pelves in Caucasian Females
- Gynaecoid, round with enlarged transverse diameter
- Android, heart-shaped (32.5%)
- Anthropoid, long AP diameter (23.5%)
- Platypelloid, long transverse diameter (2.6%)
Differences Between the Male and Female Pelves
||Thick and heavy
||Thin and light
||Narrow and deep
||Wide and shallow
|Superior pelvic aperture
||Oval or rounded
|Inferior pelvic aperture
- The parts of the bony pelvis are bound together by dense
and strong ligaments.
The Iliolumbar Ligament
- This is a strong triangular ligament that connects the tip
of the transverse process of L5
(and occasionally L4) to the iliac crest posteriorly.
- The inferior fibres of the ligament are attached to the lateral
part of the sacrum; this part called the lateral lumbosacral ligament.
- These ligaments are important because they:
- Limit rotation of L5 vertebra on the sacrum;
- And assist the vertebral articular processes in preventing
the anterior gliding of L5 on the sacrum.
The Sacrotuberous Ligament
- This passes from the sacrum to the ischial
- It has a wide attachment to the dorsal
surfaces of the sacrum and coccyx
and the PSIS.
- The fibres run inferolaterally, to the superior medial
impression on the ischial tuberosity and then extend
along its medial margin.
The Sacrospinous Ligament
- This is a thin triangular ligament that extends from the lateral
margin of the sacrum and coccyx
to the ischial spine.
- It is related anteriorly to the coccygeus muscle.
The Sacroiliac Ligaments
There were covered in Medicine 1 (ANAT1006). Click here to go to the
Joints of the Pelvis
The Lumbosacral Joints
- L5 and S1 vertebrae
articulate with each other at an anterior intervertebral joint
formed by the intervertebral disc between their bodies,
and at 2 posterior synovial joints between their articular processes.
- The L5/S1 intervertebral disc is wedge-shaped
because it is thicker anteriorly.
- The zygapophyseal (facet) joints
are synovial joints between the articular processes
(inferior ones of L5 and superior ones of S1) of the two vertebrae.
- The S1 facets face posteriorly
and medially, thereby preventing L5
vertebrae from sliding anteriorly.
The Sacrococcygeal Joint
- This joint is a secondary cartilaginous joint in which fibrocartilage and ligaments
join the articulating bones, the apex of the sacrum and the base of the coccyx.
- They are united by a thin, fibrocartilaginous
- The sacrococcygeal ligaments correspond to the anterior and posterior longitudinal
ligaments or the other intervertebral joints.
- The sacral and coccygeal cornua (L. horns) are also united by intercornual
- Until middle age, there is slight movement of the coccyx during defecation, and
considerable movement during childbirth.
- In elderly persons the sacrococcygeal joint usually becomes ossified and is obliterated.
The Sacroiliac Joints
This was covered in Medicine 1 (ANAT1006). Click
here to go to the sacroiliac joints.
The Pubic Symphysis
This was covered in Medicine 1 (ANAT1006). Click
here to go to the pubic symphysis.
Walls of the Pelvis
The Anterior Pelvic Wall
- This is formed on each side by (1) the bodies of the pubic bones,
and its superior and inferior rami, and (2) the obturator internus muscle and its
- The pubic symphysis also forms an important
part of the anterior pelvic wall.
The Lateral Pelvic Walls
- Medial to the obturator internus on
each side are the obturator nerve and vessels
and other branches of the internal iliac artery.
- The obturator internus passes from
the pelvis through the lesser sciatic foramen, and its fibres converge to form a tendon that is attached to the greater trochanter of the femur.
The Posterior Pelvic Walls
- The piriformis muscles line the posterior
- These pear-shaped muscles (L. pirum, pear + forma,
form) occupy a key position in the gluteal region (buttock).
- Each piriformis muscle leaves the pelvis
minor through the greater sciatic foramen.
The Floor of the Pelvis
- The pelvic diaphragm also separates the pelvic cavity
from the perineum.
- The musculofascial pelvic diaphragm supports the abdominopelvic viscera.
- It is slung somewhat like a funnel-shaped hammock
between the pubis anteriorly and the coccyx posteriorly.
- Laterally, it is attached to a thickening of the
obturator fascia known as the tendinous arch.
- The rectum and urethra,
and the vagina in women, penetrate the pelvic diaphragm
to reach the exterior.
The Levator Ani Muscles
- These are the largest and most important muscles in the
- Posterior to them are the coccygeus muscles, which form
the smaller part of the floor.
- The thin, broad levator ani muscles unite with its partner to form a hammock-like sheet
of muscle between the pubis anteriorly and the coccyx posteriorly, and from one lateral pelvic wall to the other.
- The levator ani muscles form most of the floor of the pelvic cavity, which separates it
from the wedge-shaped spaces known as the ischioanal
The Puborectalis Muscle
- This arises from the pubis and passes
posteriorly, where it unites with its partner to from a U-shaped
muscular sling around the anorectal junction.
- This sling maintains the anorectal flexure.
- Some fibres of the puborectalis sweep around the prostate
in males and the middle of the vagina in females and are
inserted into the central perineal ligament or tendon, or
- This is a fibromuscular mass anterior to the anus.
- These muscle fibres constitute the levator prostatae
and pubovaginalis respectively.
The Pubococcygeus Muscle
- This is the main part of the levator
- It arises from the pubis and runs
posteromedially to insert into the coccyx and anococcygeal ligament.
- The anococcygeal ligament is the median
fibrous intersection of the pubococcygeus muscles.
- It is located between the anal canal and
the tip of the coccyx.
- The pubococcygeus muscle, as it courses inferiorly and medially, encircles the urethra,
vagina, and anus and
merges into the perineal
The Iliococcygeus Muscle
- This is the thin part of the levator
- It arises on each side from the tendinous arch of the obturator fascia and the ischial spine.
- Each muscle passes medially and posteriorly
and attaches to the coccyx and anococcygeal
Innervation of the
Levator Ani Muscles
- They are innervated by the perineal branches of the 3rd and 4th sacral
nerves, which enter its pelvic surface.
Actions of the Levator
- As the pelvic diaphragm it resists the downward thrust associated with an increase of intra-abdominal pressure (e.g., coughing).
- Acting together, the levator ani muscles raise the pelvic floor, thereby assisting the anterior abdominal muscles in
compressing the abdominal and pelvic contents.
- This action is important part of forced expiration, coughing, vomiting, micturition, and
fixation of the trunk during strong movements of the upper limbs.
- The parts of the levator ani muscles that insert into the perineal body
(tendinous centre of the perineum) support the prostate
(levator prostatae) in males.
- In females, these parts support the posterior wall of the vagina (pubovaginalis).
- The parts of the levator ani muscles that insert into the wall of
the anal canal holds the anorectal junction anteriorly, thereby increasing
the angle between the rectum and anal canal.
- This prevents the passage of faeces between the rectum
and anal canal when defecation is not desired
or is inconvenient.
- When these parts contract, they raise the canal over a
descending mass of faeces, thereby aiding defecation.
- During parturition, the levator ani muscles support the
foetal head, while the cervix of the uterus is dilating.
The Coccygeus Muscles
- This is a triangular sheet of muscle that lies against
the posterior part of the iliococcygeus
muscle with which it is continuous.
- These along with the levator ani muscle form the pelvic diaphragm.
- The coccygei form the posterior and smaller
part of the pelvic floor, which is formed by the
- Lateral attachment: pelvic surfaces of ischial spine and sacrospinous
- Medial attachment: lateral margin of the coccyx and S5 vertebra.
- Innervation: branches of S4 and S5
- The coccygeus muscles assist the levator ani muscles
in supporting pelvic viscera.
- They also support the coccyx and pull
it anteriorly, elevating the pelvic floor.