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 * 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

, formed by the convergence of the inferior rami of the

ischium The ischium () form ...

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

behind, the

ischium The ischium () form ...

in front, and the ilium above; they are called the sciatic notches; in the natural state they are converted into

foramina In anatomy and osteology, a foramen (;Entry "foramen"
in

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 ...

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 * 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

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

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