The lower circumference of the
lesser pelvis
The pelvic cavity is a body cavity that is bounded by the bones of the pelvis. Its oblique roof is the pelvic inlet (the superior opening of the pelvis). Its lower boundary is the pelvic floor.
The pelvic cavity primarily contains the reproducti ...
is very irregular; the space enclosed by it is named the inferior aperture or pelvic outlet. It is an important component of
pelvimetry
Pelvimetry is the measurement of the female pelvis. It can theoretically identify cephalo-pelvic disproportion, which is when the capacity of the pelvis is inadequate to allow the fetus to negotiate the birth canal. However, clinical evidence ind ...
.
Boundaries
It has the following boundaries:
* anteriorly: the
pubic arch
The pubic arch, also referred to as the ''ischiopubic arch'', is part of the pelvis. It is formed by the convergence of the inferior rami of the ischium and pubis on either side, below the pubic symphysis. The angle at which they converge is kno ...
* laterally: the
ischial tuberosities
The ischial tuberosity (or tuberosity of the ischium, tuber ischiadicum), also known colloquially as the sit bones or sitz bones, or as a pair the sitting bones, is a large swelling posteriorly on the superior ramus of the ischium. It marks t ...
* posterolaterally: the inferior margin of the sacrotuberous ligament
* posteriorly: the anterior border of the middle of the
coccyx
The coccyx ( : coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horses. In tailless primates (e.g. humans and othe ...
.
Notches
These eminences are separated by three notches:
* one in front, the
pubic arch
The pubic arch, also referred to as the ''ischiopubic arch'', is part of the pelvis. It is formed by the convergence of the inferior rami of the ischium and pubis on either side, below the pubic symphysis. The angle at which they converge is kno ...
, formed by the convergence of the
inferior rami of the
and
pubis on either side.
* The other notches, one on either side, are formed by the
sacrum
The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30.
The sacrum situates at the upper, back part ...
and
coccyx
The coccyx ( : coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horses. In tailless primates (e.g. humans and othe ...
behind, the
in front, and the
ilium above; they are called the
sciatic notches; in the natural state they are converted into
by the
sacrotuberous
The sacrotuberous ligament (great or posterior sacrosciatic ligament) is situated at the lower and back part of the pelvis. It is flat, and triangular in form; narrower in the middle than at the ends.
Structure
It runs from the sacrum (the lower ...
and
sacrospinous ligament
The sacrospinous ligament (small or anterior sacrosciatic ligament) is a thin, triangular ligament in the human pelvis. The base of the ligament is attached to the outer edge of the sacrum and coccyx, and the tip of the ligament attaches to the sp ...
s.
In situ
When the ligaments are in situ, the inferior aperture of the pelvis is
lozenge
Lozenge or losange may refer to:
* Lozenge (shape), a type of rhombus
*Throat lozenge, a tablet intended to be dissolved slowly in the mouth to suppress throat ailments
*Lozenge (heraldry), a diamond-shaped object that can be placed on the field of ...
-shaped, bounded as follows:
* in front, by the
pubic arcuate ligament
The pubic symphysis is a secondary cartilaginous joint between the left and right superior rami of the pubis of the hip bones. It is in front of and below the urinary bladder. In males, the suspensory ligament of the penis attaches to the pubic ...
and the
inferior rami of the pubes
In vertebrates, the pubic region ( la, pubis) is the most forward-facing (ventral and anterior) of the three main regions making up the coxal bone. The left and right pubic regions are each made up of three sections, a superior ramus, inferior r ...
and
ischia
Ischia ( , , ) is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about from Naples. It is the largest of the Phlegrean Islands. Roughly trapezoidal in shape, it measures approximately east to west ...
* laterally, by the
ischial tuberosities
The ischial tuberosity (or tuberosity of the ischium, tuber ischiadicum), also known colloquially as the sit bones or sitz bones, or as a pair the sitting bones, is a large swelling posteriorly on the superior ramus of the ischium. It marks t ...
* behind, by the
sacrotuberous ligaments
The sacrotuberous ligament (great or posterior sacrosciatic ligament) is situated at the lower and back part of the pelvis. It is flat, and triangular in form; narrower in the middle than at the ends.
Structure
It runs from the sacrum (the low ...
and the tip of the
coccyx
The coccyx ( : coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horses. In tailless primates (e.g. humans and othe ...
.
See also
*
Pelvic inlet
The pelvic inlet or superior aperture of the pelvis is a planar surface which defines the boundary between the pelvic cavity and the abdominal cavity (or, according to some authors, between two parts of the pelvic cavity, called lesser pelvis and ...
Additional images
File:Gray319.png, Articulations of pelvis. Anterior view.
File:Gray320.png, Articulations of pelvis. Posterior view.
File:Low-dose CT of sagittal pelvic outlet diameter.jpg, Low-dose CT scan of sagittal pelvic outlet diameter as part of pelvimetry
Pelvimetry is the measurement of the female pelvis. It can theoretically identify cephalo-pelvic disproportion, which is when the capacity of the pelvis is inadequate to allow the fetus to negotiate the birth canal. However, clinical evidence ind ...
File:Low-dose CT scan of intertuberous diameter.jpg, Intertuberous diameter, as a measure of the transverse measure of the pelvic outlet
References
External links
* (, )
{{Authority control
Pelvis